Transition Elements Flashcards
1
Q
What is a transition element?
A
A transition element is an element whose atoms have partially filled d-orbitals or
forms at least one stable cation with partially filled d-orbitals.
2
Q
Why are Scandium and Zinc not considered transition elements?
A
• Both the scandium ion (Sc3+) and zinc ion (Zn2+) lack partially filled d-orbitals.
• Both scandium and zinc do not form coloured ions.
• Both scandium and zinc ions are restricted to single oxidation state.
3
Q
What are the characteristics/ properties of transition elements?
A
- They have high densities, melting and boiling points.
- They have variable oxidation states.
- They form a variety of complex ions.
- They form coloured ions and compounds.
- They show ability to act as catalysts.
- They show paramagnetism
4
Q
In what way does the Zinc ion show similarity to those of transition elements?
A
- Able to form complexes
5
Q
Why do transition elements have high density, melting and boiling points?
A
Explanation: The density, melting point and boiling point of metals increases with increase in the strength of the metallic bond.
Transition metals release electrons from both the inner 3d-sub energy level and the outer 4s-sub energy level towards metallic bonding resulting into very strong electrostatic attraction between the positively charged metal ions and the delocalized electrons (very strong metallic bonds) and high density/ high melting/high boiling point.
6
Q
What is the trend in melting point of the first transition series (Scandium to zinc)? Explain?
A
Trend: It increases from scandium to vanadium and generally decreases from vanadium to zinc with manganese and copper having abnormally lower melting points than expected and zinc having very low melting point.
Explanation:
• The increase from scandium is due to the increases in the number of unpaired 3d- electrons per atom contributed towards metallic bonding and the general decrease in melting point from chromium to zinc is due to decrease in the number of unpaired 3d- electrons.
• Manganese and copper have abnormally lower melting points than expected. This is because manganese has a stable half-filled 3d-sub energy level while copper has a more stable completely filled 3d-sub energy level resulting into stable lattices in which the 3d- electrons are less available for metallic bonding. This results into weak electrostatic attractions between the metal ions and the delocalized electrons (weak metallic bonds) and low melting points.
• Zinc has very low melting point because its 3d-sub energy level is completely filled and the d-electrons do not take part in metallic bonding. Only the 4s-electrons are involved in metallic bonding resulting into weak electrostatic attractions between the zinc ions and the delocalized electrons and low melting points.
7
Q
Why do transition elements form coloured compounds/ions?
A
Explanation:
Formation of coloured compounds by transition metal ions is due to presence incompletely filled 3d-orbitals.
When white light is shone onto transition metal ions or in presence of ligands, the 3d-orbitals split into two sub energy levels.
A photon of energy is absorbed in the visible spectrum when an electron jumps from the lower sub- energy level to the high energy level.
The unabsorbed visible light is transmitted and it is the observed colour.
8
Q
What factors affect the absorbed energy and the colour of the transition element ion?
A
• The nature of the metal ion
• The oxidation state of the cation e.g. Fe2+, Fe3+
• The nature of ligand e.g.
̅̅− 𝑂𝐻,𝐶𝑁,𝐶𝑙 ,𝐻2𝑂, 𝑁𝐻3
• The geometry of the complex e.g. tetrahedral, octahedral
9
Q
Explain how transition elements are paramagnetic (weakly attracted by a magnetic field).
A
Transition metal ions show paramagnetism due to presence unpaired 3d-electrons which spin on their axis creating a magnetic dipole.
The spins become temporarily aligned in the same direction the external applied magnetic field, causing the material to be attracted to the applied magnetic field.
Paramagnetic character increases with the number of unpaired 3d- electrons.
For example
(i) Mn2+ (1𝑠22𝑠22𝑝63𝑠23𝑝63𝑑5) is more paramagnetic than Mn4+
(1𝑠22𝑠22𝑝63𝑠23𝑝63𝑑3) because Mn2+ has five unpaired electrons while Mn4+ has only three unpaired electrons.
10
Q
Why do transition metals and their compounds make good heterogeneous catalysts?
A
- The presence of partially filled d-orbitals allows them to form weak bonds with the reactants on the catalyst surface, increasing the reactant concentration at adsorption sites. This weakens the reactant bonds resulting in an increased rate of reaction.
- Their variable oxidation states which allows them to create an alternative path for the reaction with lower activation energy.
Note: During the reaction the catalyst undergoes change in oxidation state but it is regenerated at the end of the reaction.
11
Q
What is a complex?
A
• A complex is a substance in which a central metal atom or ion is bonded to negative ions or neutral molecules with lone pairs of electrons through coordinate bonding.
• The negative ions or neutral molecules with lone pairs of electrons are called ligands.
12
Q
What is coordination number?
A
• The number of coordinate bonds on the central metal atom or ion by ligands
13
Q
Why do transition metals form many complexes?
A
(i) their high polarizing power arising from their small highly charged ions enabling them to attract lone pairs from ligands.
(ii) the presence of vacant d-orbitals that can accommodate lone pairs of electrons from ligands.
14
Q
What is Ionization isomerism?
A
These differ in the distribution of ions between those which directly bonded and those not directly bonded to the central metal atom or ion.
15
Q
What is Hydration isomerism?
A
These differ in the number of water molecules directly bonded to the central metal atom or ion.
16
Q
Give the properties of vanadium
A
• It is very strong metal
• It is resistant to corrosion at ordinary conditions and only combines with air at high temperatures
• It is not attacked by cold dilute acids but slowly dissolves in hot concentrated nitric acid, hot concentrated sulphuric acid and concentrated hydrochloric acid.
17
Q
How can the oxidation states of vanadium be demonstrated?
A
By shaking a solution ammonium vanadate in dilute sulphuric acid with zinc amalgam.
The solution changes colour from pale-yellow to blue, to green and finally to lavender.
18
Q
Why don’t V5+ and V4+ exist as bare ions in aqueous solutions?
A
Both ions are highly charged and have very small ionic radii and as a result they exert a high polarizing effect on the neighboring water molecules and detaching oxide ions from the water molecules forming VO3- (or VO2+) and VO2+ ions respectively.
19
Q
How is Vanadium(V) oxide, V2O5 prepared?
A
- It is an orange solid prepared by heating ammonium metavanadate, NH4VO3.
20
Q
What type of oxide is vanadium (v) oxide?
A
It is an amphoteric oxide.
21
Q
How does vanadium (v) oxide react in strongly alkaline solutions?
A
It dissolves forming orthovanadate ion, VO43-
Potassium hydroxide and potassium chlorate(V).
3MnO2 (s) + KClO3 (l) + 6KOH(l) → 3K2MnO4 (l) + KCl(l) + 3H2O(l)or − ̅ 2− −
3𝑀𝑛𝑂2(𝑙) + 𝐶𝑙𝑂3 (𝑙) + 6𝑂𝐻(𝑙) → 3𝑀𝑛𝑂4 (𝑎𝑞) + 𝐶𝑙 (𝑎𝑞) + 3𝐻2𝑂(𝑙)
• Potassium manganate(VI) is only stable in alkaline conditions.
In neutral or acidic conditions it disproportionates into manganate(VII) ions and manganese(IV) oxide.
18
3𝑀𝑛𝑂42−(𝑎𝑞) + 4𝐻+(𝑎𝑞) → 2𝑀𝑛𝑂4−(𝑎𝑞) + 𝑀𝑛𝑂2(𝑠) + 2𝐻2𝑂(𝑙)(𝑨𝒄𝒊𝒅𝒊𝒄 𝒎𝒆𝒅𝒊𝒖𝒎
2− −
3𝑀𝑛𝑂4 (𝑎𝑞) + 2𝐻2𝑂(𝑙) ⇌ 2𝑀𝑛𝑂4 (𝑎𝑞) + 𝑀𝑛𝑂2(𝑠) + 4𝑂𝐻(𝑎𝑞)(𝑨𝒍𝒌𝒂𝒍𝒊𝒏𝒆 𝒎𝒆𝒅𝒊𝒖𝒎)
Manganese(VII) compounds
Potassium manganate(VII)
This is the most important compound in the +7 oxidation state of manganese. It is a dark purple crystalline solid. It is moderately soluble in water.
Reactions of potassium manganate(VII)
̅
19
22
Q
How does vanadium (v) oxide react in strongly acidic conditions?
A
It dissolves forming VO2+ ion
VO (s) + 2H+(aq) → 2VO +(aq)+H O(l)
23
Q
How does chromium metal react with oxygen?
A
It burns in oxygen at 2300K forming chromium(III) oxide, a dark-green solid
4Cr(s) + 3O2 (g) → 2Cr2O3 (s)
24
Q
How does chromium react with cold dilute hydrochloric and cold dilute sulphuric acid?
A
- It reacts slowly but more rapidly on warming forming chromium(II) salts (blue solution) and hydrogen gas
Cr(s) + 2H+ (aq) → Cr2+ (aq) + H2 (g)
25
What happens to chromium(II) salts in acidic conditions?
They are readily oxidized to chromium(III) salts (green solution).
4Cr2+ (aq) + 4H+ (aq) + O2 (g) → 4Cr3+ (aq) + 2H2O(l)
26
What factors favor complex ion formation?
- Small highly charged cations / Cations with high charge density and polarizing power
- Presence of vacant orbitals on the central metal ion or atom
- Presence of lone pairs of electrons on the ligands
27
How does chromium react with concentrated sulphuric acid
It forms chromium(III) sulphate (green
solution), sulphurdioxide and water.
28
How does chromium react with nitric acid?
Chromium is rendered passive by nitric acid.
29
What is the reaction between chlorine and chromium?
When heated in a stream of dry chlorine chromium(III) chloride is formed
2Cr(s) + 3Cl2 (g) → 2CrCl3 (s)
30
Which oxidation states does chromium exist in in compounds?
- +6 which is oxidizing
- +3 which is the most stable
- +2 which is reducing
31
How is chromium(II) chloride formed?
It is a white solid prepared by heating chromium in a stream of dry hydrogen chloride gas
Cr(s) + 2HCl(g) → CrCl2 (s) + H2 (g)
32
How is chromium(III) oxide prepared?
It is a green solid prepared by heating ammonium dichromate(VI)
(NH4 )2Cr2O7 (s) → Cr2O3 (s) + N2 (g) + 4H2O(l)
33
True or false
Chromium(III) oxide may be reduced by carbon and oxygen
False
Cr2O3 is very stable and resists reduction by both carbon and hydrogen
34
Is Cr2O3 basic, acidic or amphoteric?
Amphoteric with basic character being predominant.
35
How does Chromium(III) oxide react with acids?
It dissolves forming a green solution consisting of a chromium(III) salt.
Cr2O3 (s) + 6H+ (aq) → 2Cr3+ (aq) + 3H2O(l)
36
How does Chromium(III) oxide react with alkalis?
It dissolves forming a deep-green solution consisting of a complex of
hexahydroxochromate(III) ions or tetrahydroxochromate(III) ions
37
What color is Chromium(III) hydroxide?
It is a green solid
38
How is Chromium(III) hydroxide prepared?
By adding a calculated amount of aqueous sodium hydroxide to an aqueous solution of a chromium(III) salt.
Cr3+ (aq) + 3OH− (aq) → Cr(OH)3 (s)
39
Is Chromium(III) hydroxide basic, acidic or amphoteric?
Amphoteric
40
True or false, Chromium(III) hydroxide can react with both alkalis and acids.
True
With acids: Cr(OH)3(s) + 3H+(aq) Cr3+(aq) + 3H2O(l) ̅-
With alkalis: Cr(OH)3(s) + 𝑂𝐻(aq) [Cr(OH)4] (aq) ̅ 3-
Cr(OH)3(s) + 3𝑂𝐻(aq) [Cr(OH)6] (aq)
41
What color is Anhydrous chromium(III), CrCl3?
It is a reddish-violet solid
42
How is Anhydrous chromium(III) chloride prepared?
By heating chromium in a stream of dry chlorine gas.
2Cr(s) + 3Cl2 (g) → 2CrCl3 (s)
43
How may the three isomers of Hydrated chromium(III) chloride complex be distinguished?
By titrating each with standard silver nitrate solution to find the number of moles silver chloride precipitated per mole of the isomer.
44
Why are aqueous solutions of chromium(III) salts acidic?
The chromium(III) ion has a high charge density and polarizing power.
Therefore it exerts a strong attraction for a lone pair of electrons on water molecules forming a complex of hexaaquachromium(III) ions, [Cr(H2O)6]3+.
The strong chromium – oxygen coordinate bond formed weakens the oxygen-hydrogen bond (O – H) of the water molecule and releasing hydrogen ions.
The hydrogen ions make the solution acidic.
[𝐶𝑟(𝐻2𝑂)6]3+(𝑎𝑞) ⇌ [𝐶𝑟(𝐻2𝑂)5𝑂𝐻]2+(𝑎𝑞) + 𝐻+(𝑎𝑞)
45
Explain what is observed when aqueous sodium carbonate is added to an aqueous solution of chromium(III) ions?
Observation: A green precipitate and effervescence of a colourless gas
Explanation: The green precipitate is chromium(III) hydroxide and the colourless gas is carbon dioxide.
The chromium(III) ions combine with carbonate ions forming chromium(III) carbonate.
2Cr3+(aq) + 3CO32-(aq) Cr2(CO3)3(s)
The chromium(III) ion has a small ionic radius and a big positive charge resulting into high charge density and polarizing power.
Chromium(III) carbonate is therefore readily hydrolyzed by water forming chromium(III) hydroxide and carbon dioxide gas.
Cr2(CO3)3(s) + 3H2O(l) 2Cr(OH)3(s) + 3CO2(g)
Overall equation:
2Cr3+(aq) + 3CO32-(aq) + 3H2O(l) 2Cr(OH)3(s) + 3CO2(g)
46
Explain what is observed when chromium(III) ions is reacted with aqueous sodium hydroxide?
Observation: A green precipitate soluble in excess forming a green solution.
Explanation:
The green precipitate is chromium(III) hydroxide which is insoluble in water.
𝐶𝑟3+(𝑎𝑞) + 3𝑂𝐻(𝑎𝑞) → 𝐶𝑟(𝑂𝐻)3(𝑠)
Chromium(III) hydroxide is amphoteric and reacts with excess sodium hydroxide solution forming a soluble complex of tetrahydroxochromate(III) ions.
𝐶𝑟(𝑂𝐻)3(𝑠)+𝑂𝐻(𝑎𝑞)→[𝐶𝑟(𝑂𝐻)4] (𝑎𝑞)
47
What happens when the green solution of tetrahydrochromate(III) ions is boiled with hydrogen peroxide?
A yellow solution containing chromate(VI) ions is formed.
2[𝐶𝑟(𝑂𝐻)4] (𝑎𝑞)+3𝐻2𝑂2(𝑎𝑞)+2𝑂𝐻(𝑎𝑞)→2𝐶𝑟𝑂4 (𝑎𝑞)+8𝐻2𝑂(𝑙)
48
What is observed from the reaction between chromate(VI) ions and aqueous lead(II) nitrate or lead(II) ethanoate?
When to the yellow solution of chromate(VI) ion is added aqueous lead(II) nitrate or lead(II) ethanoate, a yellow precipitate is formed.
Pb2+ (aq) + CrO 2− (aq) → PbCrO (s)
49
What happens when to the yellow solution of chromate(VI) ions is added aqueous barium chloride or barium nitrate?
A yellow precipitate of barium chromate is formed.
𝐵𝑎2+(𝑎𝑞) + 𝐶𝑟𝑂42−(𝑎𝑞) → 𝐵𝑎𝐶𝑟𝑂4(𝑠)
50
What happens when to the yellow solution of chromate(VI) ions is added a layer of butan-1-ol (or ether) followed by excess dilute sulphuric and hydrogen peroxide?
A blue solution is formed in the ether layer due to formation of chromium(VI) oxide peroxide which is more soluble in ether than water.
2𝐶𝑟𝑂42−(𝑎𝑞) + 4𝐻+(𝑎𝑞) + 4𝐻2𝑂2(𝑎𝑞) → 2𝐶𝑟𝑂5(𝑎𝑞) + 6𝐻2𝑂(𝑙)
51
What is observed when to the yellow solution of chromate(VI) ions is added aqueous silver nitrate?
A brick red precipitate of silver chromate is formed.
2𝐴𝑔+(𝑎𝑞) + 𝐶𝑟𝑂 2−(𝑎𝑞) → 𝐴𝑔 𝐶𝑟𝑂 (𝑠)
52
What is the result of heating strongly, chromium(VI) oxide?
CrO3 decomposes forming a green residue of chromium(III) oxide and liberating oxygen gas.
4CrO3 (s) → 2Cr2O3 (s) + 3O2 (g)
53
What type of oxide is Chromium(VI) oxide?
CrO3 is an acidic oxide
54
How does Chromium(VI) oxide react with alkalis?
Reacts forming a yellow solution consisting of chromate(VI) ions
𝐶𝑟𝑂3(𝑠) + 2𝑂𝐻(𝑎𝑞) → 𝐶𝑟𝑂4 + 𝐻2𝑂(𝑙)
55
How are Barium, strontium and lead chromates formed?
They are yellow crystalline solids prepared as yellow precipitates by reacting aqueous solutions of the metal ions with aqueous potassium chromate
Ba2+ (aq) + CrO 2− (aq) → BaCrO (s)
Sr2+ (aq) + CrO 2− (aq) → SrCrO (s)
Pb2+ (aq) + CrO 2− (aq) → PbCrO (s)
56
How is Silver chromate made?
It is a red crystalline solid made by reacting silver nitrate with potassium chromate (VI)
2Ag+(aq)+CrO 2−(s) → Ag CrO (s)
57
How do chromate(VI) ions react with dilute acids?
Aqueous solutions of chromate (VI) ions are converted to dichromate(VI) ions when reacted with dilute acids.
The yellow colour of chromate(VI) ions changes to orange of dichromate(VI) ions.
(Yellow) (Orange)
58
What is the physical appearance of sodium dichromate(VI)?
- It is a red crystalline solid.
59
How is sodium dichromate(VI) prepared?
- By reacting sodium chromate with dilute sulphuric acid.
60
What precipitates out first when the mixture from the preparation of sodium dichromate(VI) is cooled?
- Sodium sulphate crystals (Na2SO4.10H2O).
61
How are the red crystals of sodium dichromate(VI) formed after the initial precipitation?
- By concentrating the remaining solution through evaporation and then cooling it.
62
Describe the solubility and deliquescent properties of sodium dichromate(VI).
- Sodium dichromate(VI) is deliquescent and soluble in water.
63
Why can’t sodium dichromate(VI) be used as a primary standard?
- Because it is deliquescent.
64
How is potassium dichromate(VI) made?
- By mixing hot, almost saturated solutions of sodium dichromate(VI) and potassium chloride.
65
What happens to the sodium chloride formed in the reaction for making potassium dichromate(VI)?
- It is filtered out, and the hot filtrate is left to cool, forming crystals of potassium dichromate(VI).
66
What is the equilibrium equation for the formation of dichromate(VI) ions from chromate(VI) ions in acidic solutions?
- 2CrO4^2−(aq) + 2H+(aq) ⇌ Cr2O7^2−(aq) + H2O(l)
67
Why is potassium dichromate(VI) considered a primary standard?
- Because it is not deliquescent and can be obtained in a state of high purity.
68
What is potassium dichromate(VI) used for in titration?
- It is used to standardize sodium thiosulphate solution.
69
What happens to dichromate(VI) ions when they react with alkalis?
- They are converted to chromate(VI) ions, and the solution changes color from orange to yellow.
70
What is the color change observed when dichromate(VI) ions are converted to chromate(VI) ions in alkali?
- From orange to yellow.
71
What happens to dichromate(VI) ions in acidic media during redox reactions?
- They act as powerful oxidizing agents and are reduced to green chromium(III) ions.
72
What is the balanced chemical equation for the reduction of dichromate(VI) ions to chromium(III) ions in acidic media?
- Cr2O7^2−(aq) + 14H+(aq) + 6e− → 2Cr3+(aq) + 7H2O(l)
73
What color change occurs when dichromate(VI) ions are reduced to chromium(III) ions in acidic media?
- From orange to green.
74
What does acidified potassium dichromate(VI) oxidize iron(II) ions to?
- Iron(III) ions.
75
What is the balanced chemical equation for the oxidation of iron(II) ions by acidified potassium dichromate(VI)?
- Cr2O7^2−(aq) + 14H+(aq) + 6Fe2+ → 2Cr3+(aq) + 6Fe3+(aq) + 7H2O(l)
76
What does acidified potassium dichromate(VI) oxidize aqueous potassium iodide to?
- Iodine.
77
What is the balanced chemical equation for the oxidation of potassium iodide by acidified potassium dichromate(VI)?
- Cr2O7^2−(aq) + 14H+(aq) + 6I− → 2Cr3+(aq) + 3I2(aq) + 7H2O(l)
78
What color change is observed when potassium iodide is oxidized to iodine by acidified potassium dichromate(VI)?
- From colorless to brown.
79
What indicator is used in the titration of iodine with aqueous sodium thiosulphate?
- Starch indicator.
80
What is the balanced chemical equation for the titration of iodine with aqueous sodium thiosulphate?
- I2(aq) + 2S2O3^2−(aq) → 2I−(aq) + S4O6^2−(aq)
81
What is the most important ore of manganese?
- Pyrolusite (MnO2)
82
How does pure manganese react with air when finely divided and heated?
- It burns to form Mn3O4.
83
What is the balanced chemical equation for manganese burning in air?
- 3Mn(s) + 2O2(g) → Mn3O4(s)
84
How does manganese react with hot water?
- It forms manganese(II) hydroxide and hydrogen gas.
85
What is the balanced chemical equation for manganese reacting with hot water?
- Mn(s) + 2H2O(l) → Mn(OH)2(s) + H2(g)
86
How does manganese react with dilute hydrochloric acid and dilute sulphuric acid?
- It dissolves, forming the corresponding salt and liberating hydrogen gas.
87
What is the balanced chemical equation for manganese reacting with dilute acids?
- Mn(s) + 2H+(aq) → Mn2+(aq) + H2(g)
88
What are the products of manganese reacting with hot concentrated sulphuric acid?
- Manganese(II) sulphate, sulphur dioxide, and water.
89
What is the balanced chemical equation for manganese reacting with hot concentrated sulphuric acid?
- Mn(s) + 2H2SO4(l) → MnSO4(aq) + SO2(g) + 2H2O(l)
90
In what oxidation states does manganese commonly exist?
- +2, +3, +4, +5, +6, and +7.
91
Which oxidation state of manganese is the most unstable and least common?
- +5 oxidation state.
92
Which oxidation state of manganese is the most powerful oxidizing?
- +7 oxidation state.
93
Which oxidation state of manganese is the most stable?
- +2 oxidation state.
94
Why is the +2 oxidation state of manganese the most stable?
- Because manganese has a half-filled 3d subshell in this state, which is thermodynamically very stable (Mn2+: 1s^22s^22p^63s^23p^63d^5).
95
What is the appearance and preparation method of manganese(II) oxide, MnO?
- It is a grey-green solid prepared by heating manganese(II) carbonate or manganese(II) ethanedioate.
96
What are the balanced chemical equations for preparing manganese(II) oxide from manganese(II) carbonate and manganese(II) ethanedioate?
- MnCO3(s) → MnO(s) + CO2(g)
- MnC2O4(s) → MnO(s) + CO(g) + CO2(g)
97
What is the appearance and preparation method of manganese(II) hydroxide, Mn(OH)2?
- It is a white solid prepared by precipitation when aqueous sodium hydroxide is added to an aqueous solution of a manganese(II) salt.
98
What is the balanced chemical equation for the precipitation of manganese(II) hydroxide?
- Mn2+(aq) + 2OH−(aq) → Mn(OH)2(s)
99
What happens to manganese(II) hydroxide when it stands in air?
- It is readily oxidized to hydrated manganese(III) oxide, Mn2O3.xH2O, which is a brown solid.
100
What is the balanced chemical equation for the oxidation of manganese(II) hydroxide by air?
- 4Mn(OH)2(s) + O2(g) → 2Mn2O3.2H2O(s)
101
What happens to manganese(II) hydroxide when it reacts with hydrogen peroxide?
- It is oxidized to manganese(IV) oxide, a black solid.
102
What is the balanced chemical equation for the oxidation of manganese(II) hydroxide by hydrogen peroxide?
- Mn(OH)2(s) + H2O2(aq) → MnO2(s) + 2H2O(l)
103
What is the chemical formula for manganese(II) carbonate?
- MnCO3
104
What is the appearance of manganese(II) carbonate?
- It is a brown-red solid.
105
How is manganese(II) carbonate prepared?
- By precipitating it from a reaction between aqueous sodium carbonate and an aqueous solution of a manganese(II) salt.
106
What is the balanced chemical equation for the preparation of manganese(II) carbonate?
- Mn2+(aq) + CO3^2−(aq) → MnCO3(s)
107
What are the common manganese(II) salts and their appearance?
- Manganese(II) chloride, sulphate, and nitrate are all pink solids.
108
How are manganese(II) chloride, sulphate, and nitrate prepared?
- By reacting excess manganese(II) oxide (MnO), manganese(II) hydroxide (Mn(OH)2), or manganese(II) carbonate (MnCO3) with the corresponding dilute acid.
109
What is the process after reacting manganese(II) compounds with dilute acids to form manganese(II) salts?
- The excess solid is filtered off, the filtrate is concentrated by evaporation, and then left to cool to form crystals of the salt.
110
How do Mn2+ ions exist in aqueous solutions?
- As [Mn(H2O)6]2+ complex, which is a pink solution.
111
How can Mn2+(aq) be detected with aqueous sodium hydroxide?
- By adding it dropwise until in excess, forming a white precipitate that turns brown on standing.
112
What is the balanced chemical equation for the reaction of Mn2+(aq) with aqueous sodium hydroxide?
- Mn2+(aq) + 2OH−(aq) → Mn(OH)2(s)
113
How can Mn2+(aq) be detected with aqueous ammonia?
- By adding it dropwise until in excess, forming a white precipitate that turns brown on standing.
114
What happens when Mn2+(aq) reacts with solid sodium bismuthate(V) or lead(IV) oxide and concentrated nitric acid?
- A purple solution is observed due to the formation of manganate(VII) ions.
115
What is the balanced chemical equation for the reaction of Mn2+(aq) with sodium bismuthate(V)?
- 2Mn2+(aq) + 5BiO3−(s) + 14H+(aq) → 2MnO4−(aq) + 5Bi3+(aq) + 7H2O(l)
116
What is the balanced chemical equation for the reaction of Mn2+(aq) with lead(IV) oxide?
- 2Mn2+(aq) + 5PbO2(s) + 4H+(aq) → 2MnO4−(aq) + 5Pb2+(aq) + 2H2O(l)
117
What happens to manganese(III) compounds in aqueous solution?
- They tend to disproportionate, forming a pale-pink (or colorless) solution of manganese(II) ions and a black solid of manganese(IV) oxide.
118
What is the balanced chemical equation for the disproportionation of manganese(III) ions in aqueous solution?
- 2Mn3+(aq) + 2H2O(l) → Mn2+(aq) + MnO2(s) + 4H+(aq)
119
What is the chemical formula for manganese(III) oxide?
- Mn2O3
120
What is the appearance of manganese(III) oxide?
- It is a brown solid.
121
How is manganese(III) oxide prepared?
- By heating manganese(IV) oxide in ammonia gas.
122
What is the balanced chemical equation for the preparation of manganese(III) oxide?
- 6MnO2(s) + 2NH3(g) → 3Mn2O3(s) + MnO2(s) + 3H2O(l) + N2(g)
123
What is the chemical formula for trimanganese tetraoxide?
- Mn3O4
124
What is the appearance of trimanganese tetraoxide?
- It is a red solid.
125
How is trimanganese tetraoxide prepared by heating manganese(IV) oxide?
- By strongly heating manganese(IV) oxide.
126
What is the balanced chemical equation for the preparation of Mn3O4 by heating manganese(IV) oxide?
- 3MnO2(s) → 2Mn3O4(s) + O2(g)
127
How is trimanganese tetraoxide prepared by heating manganese(II) oxide?
- By strongly heating manganese(II) oxide in air.
128
What is the balanced chemical equation for the preparation of Mn3O4 by heating manganese(II) oxide in air?
- 6MnO(s) + O2(g) → 2Mn3O4(s)
129
What happens when Mn3O4 dissolves in cold concentrated sulphuric acid?
- It forms manganese(II) and manganese(III) sulphates.
130
What is the balanced chemical equation for Mn3O4 dissolving in cold concentrated sulphuric acid?
- Mn3O4(s) + 8H+(aq) → Mn2+(aq) + 2Mn3+(aq) + 4H2O(l)
131
What happens when Mn3O4 dissolves in hot concentrated nitric acid?
- It forms manganese(IV) oxide and manganese(II) nitrate.
132
What is the balanced chemical equation for Mn3O4 dissolving in hot concentrated nitric acid?
- Mn3O4(s) + 4H+(aq) → MnO2(s) + 2Mn2+(aq) + 2H2O(l)
133
What is the naturally occurring form of manganese(IV) oxide?
- Pyrolusite, MnO2
134
What is the appearance of manganese(IV) oxide?
- It is a black solid and insoluble in water.
135
How is manganese(IV) oxide prepared?
- By heating manganese(II) nitrate.
136
What is the balanced chemical equation for the preparation of MnO2 by heating manganese(II) nitrate?
- Mn(NO3)2(s) → MnO2(s) + 2NO2(g)
137
What property does manganese(IV) oxide have as an oxidizing agent?
- It is a powerful oxidizing agent.
138
How does manganese(IV) oxide react with warm concentrated hydrochloric acid?
- It oxidizes hydrochloric acid to chlorine gas and is reduced to manganese(II) chloride.
139
How does manganese(IV) oxide react with warm concentrated hydrochloric acid?
- It oxidizes hydrochloric acid to chlorine gas and is reduced to manganese(II) chloride.
140
What is the balanced chemical equation for the reaction of MnO2 with hydrochloric acid?
- MnO2(s) + 4HCl(aq) → MnCl2(aq) + Cl2(g) + 2H2O(l)
141
How does manganese(IV) oxide react with hot dilute sulphuric acid and oxalic acid?
- It oxidizes oxalic acid to carbon dioxide and is reduced to manganese(II) sulphate.
142
What is the balanced chemical equation for the reaction of MnO2 with oxalic acid and sulphuric acid?
- MnO2(s) + 4H+(aq) + C2O4^2−(aq) → Mn2+(aq) + 2CO2(g) + 2H2O(l)
143
What is added to a fixed mass of pyrolusite to estimate MnO2 content?
- Excess potassium iodide solution and excess concentrated hydrochloric acid.
144
What indicator is used in the titration for estimating MnO2 in pyrolusite?
- Starch indicator.
145
What standard solution is used to titrate the solution for MnO2 estimation?
- Standard sodium thiosulphate solution.
146
What volume is recorded during the titration for MnO2 estimation?
- The volume of sodium thiosulphate needed to reach the endpoint.
147
How can the percentage of MnO2 in the original pyrolusite sample be calculated?
- Using the stoichiometry of the reactions involved.
148
Write the balanced equation for the reaction of MnO2 with hydrochloric acid.
- MnO2 (s) + 4HCl(aq) → MnCl2 (aq) + Cl2 (g) + 2H2O(l)
149
Write the balanced equation for the reaction of chlorine gas with iodide ions.
- Cl2 (g) + 2I− (aq) → 2Cl− (aq) + I2 (aq)
150
Write the balanced equation for the titration of iodine with sodium thiosulphate.
- I2 (aq) + 2S2O3^2−(aq) → 2I−(aq) + S4O6^2−(aq)
151
What is the chemical formula for potassium manganate(VI)?
- K2MnO4
152
Describe the appearance of potassium manganate(VI).
- It is a green solid.
153
How is potassium manganate(VI) prepared?
- By fusing a mixture of manganese(IV) oxide, potassium hydroxide, and potassium chlorate(V).
154
Write the balanced equation for the preparation of potassium manganate(VI).
- 3MnO2 (s) + KClO3 (l) + 6KOH(l) → 3K2MnO4 (l) + KCl(l) + 3H2O(l)
155
Under what conditions is potassium manganate(VI) stable?
- In alkaline conditions.
156
What happens to potassium manganate(VI) in neutral or acidic conditions?
- It disproportionates into manganate(VII) ions and manganese(IV) oxide.
157
Write the balanced equation for the disproportionation of manganate(VI) ions in acidic conditions.
- 3MnO4^2−(aq) + 4H+(aq) → 2MnO4−(aq) + MnO2(s) + 2H2O(l)
158
Write the balanced equation for the disproportionation of manganate(VI) ions in alkaline conditions.
- 3MnO4^2−(aq) + 2H2O(l) ⇌ 2MnO4−(aq) + MnO2(s) + 4OH−(aq)
159
What is the chemical formula for potassium manganate(VII)?
- KMnO4
160
Describe the appearance and solubility of potassium manganate(VII).
- It is a dark purple crystalline solid and moderately soluble in water.
161
What happens to potassium manganate(VII) on strong heating?
- It decomposes to potassium manganate(VI), manganese(IV) oxide, and oxygen.
162
Write the balanced equation for the decomposition of potassium manganate(VII) on heating.
- 2KMnO4 (s) → K2MnO4 (s) + MnO2 (s) + O2 (g)
163
What kind of agent is potassium manganate(VII) and in what conditions?
- It is a powerful oxidizing agent, especially in acidic conditions.
164
Write the half-equation for the reduction of potassium manganate(VII) in acidic conditions.
- MnO4− (aq) + 8H+ (aq) + 5e− → Mn2+ (aq) + 4H2O(l)
165
What happens to the color of potassium manganate(VII) during its reaction with oxalate ions?
- The purple color changes to colorless.
166
Write the balanced equation for the reaction of potassium manganate(VII) with oxalate ions in acidic conditions.
- 2MnO4−(aq) + 16H+(aq) + 5C2O4^2−(aq) → 2Mn2+(aq) + 8H2O(l) + 10CO2(g)
167
What is the balanced equation for the reaction of potassium manganate(VII) with iron(II) salts?
- MnO4− (aq) + 8H+ (aq) + 5Fe2+ (aq) → Mn2+ (aq) + 5Fe3+ (aq) + 4H2O(l)
168
What is the observable color change when potassium manganate(VII) reacts with iron(II) salts?
- The purple color of potassium manganate(VII) changes to colorless.
169
What ions are produced when potassium manganate(VII) reacts with iron(II) salts?
- Manganese(II) ions (Mn2+) and iron(III) ions (Fe3+).
170
What is the balanced equation for the reaction of potassium manganate(VII) with hydrogen peroxide solution?
- 2MnO4−(aq) + 6H+(aq) + 5H2O2(aq) → 2Mn2+(aq) + 5O2(g) + 8H2O(l)
171
What is the observable color change when potassium manganate(VII) reacts with hydrogen peroxide?
- The purple color of potassium manganate(VII) changes to colorless.
172
What is the balanced equation for the reaction of potassium manganate(VII) with potassium iodide solution?
- 2MnO4−(aq) + 16H+(aq) + 10I−(aq) → 2Mn2+(aq) + 5I2(g) + 8H2O(l)
173
What is the observable color change when potassium manganate(VII) reacts with potassium iodide solution?
- The purple color of potassium manganate(VII) is discharged, and a brown solution is formed.
174
What is the balanced equation for the reaction of potassium manganate(VII) with hydrogen sulphide?
- 2MnO4−(aq) + 5H2S(g) + 6H+(aq) → 2Mn2+(aq) + 5S(s) + 8H2O(l)
175
What precipitate forms when potassium manganate(VII) reacts with hydrogen sulphide?
- A yellow precipitate of sulphur (S).
176
What happens to potassium manganate(VII) in slightly acidic conditions exposed to light?
- Potassium manganate(VII) decomposes to form black solid particles of manganese(IV) oxide (MnO2).
177
Why is potassium manganate(VII) not considered a primary standard?
- Potassium manganate(VII) cannot be obtained in a high degree of purity as samples of the substance contain some manganese(IV) oxide, and it slowly decomposes into manganese(IV) oxide in slightly acidic conditions.
178
In what type of bottle is potassium manganate(VII) stored and why?
- Potassium manganate(VII) is stored in brown bottles to prevent decomposition catalyzed by light.
179
What substances can standardize solutions of potassium manganate(VII) in volumetric analysis?
- Sodium ethanedioate (Na2C2O4) in the presence of excess dilute sulfuric acid at about 60°C, and ammonium iron(II) sulfate ((NH4)2SO4.FeSO4.6H2O) in the presence of excess dilute sulfuric acid.
180
Why is no indicator required when potassium manganate(VII) is used in volumetric analysis?
- The endpoint is indicated by a persistent pink color of the solution.
181
Why is dilute hydrochloric acid not used to acidify potassium manganate(VII) during volumetric analysis?
- Potassium manganate(VII) oxidizes hydrochloric acid to chlorine, reducing the concentration of the manganate(VII) solution.
182
What happens when potassium manganate(VII) reacts with hydrochloric acid?
- 2MnO4− (aq) + 16H+ (aq) + 10Cl− (aq) → 2Mn2+ (aq) + 5Cl2 (g) + 8H2O(l)
183
Name the principle ores of iron.
Haematite (Iron(III) oxide)
Magnetite (Tri-iron tetraoxide)
Siderite (Iron(II) carbonate)
184
What are the raw materials used in the extraction of iron from Haematite?
- Iron ore (Haematite)
- Limestone (CaCO₃)
- Coke (C)
185
Describe the extraction of iron from haematite.
Iron is extracted from its ore from in a blast furnace made up of steel with the inner region lined with firebricks.
- The iron ore, limestone and coke in their correct proportions are fed into the top of the furnace.
- Pre-heated air at a temperature of 600oC is injected into the furnace through pipes called tuyeres.
- The coke burns in the hot compressed air forming carbon dioxide in an exothermic reaction raising the temperature to about 1900oC.
C(s)+O2(g) → CO2(g)
- The carbon dioxide gas is reduced by hot unburnt coke forming carbon monoxide in an endothermic reaction reducing the temperature to about 1100oC.
C(s) + CO2 (g) → 2CO(g)
- At about 700oC, carbon monoxide reduces the iron ore to iron which falls to the bottom of the furnace where temperature is high enough to melt it.
- Fe2O3 (s) + 3CO(g) → 2Fe(l) + 3CO2 (g)
- At a temperature of 800oC limestone decomposes to calcium oxide and carbon dioxide. 800oC
CaCO3 (s) ⎯⎯⎯→ CaO(s) + CO2 (g)
- The calcium oxide combines with acidic impurities, mainly silicon (IV) oxide and aluminium oxide forming slag (molten calcium silicate and calcium aluminate).
CaO(s) + SiO2 (s) → CaSiO3 (l) CaO(s) + Al2O3 (s) → CaAl2O4 (l)
- Both the molten iron and molten slag sink to the base of the furnace where the less dense slag floats on top of molten iron.
- The two layers are tapped off periodically at different levels. The molten iron is run into moulds of sand forming pig-iron.
Note: If spathic iron (FeCO3) or Iron pyrite (FeS2) ore is used, the ore is first roasted to convert it into iron(III) oxide before feeding it into the Blast furnace.
4𝐹𝑒𝐶𝑂3(𝑠) + 𝑂2(𝑔) → 2𝐹𝑒2𝑂3(𝑠) + 4𝐶𝑂2(𝑔)
4𝐹𝑒𝑆2(𝑠) + 11𝑂2(𝑔) → 2𝐹𝑒2𝑂3(𝑠) + 8𝑆𝑂2(𝑔)
186
What happens when iron reacts with oxygen at room temperature?
- Iron is not affected by dry air (oxygen) at room temperature.
187
Describe the reaction of iron with oxygen when heated strongly.
- When heated strongly, iron combines with oxygen to form tri-iron tetraoxide, a blue-black residue.
188
What happens when iron reacts with concentrated sulphuric acid?
- Iron reacts with concentrated sulphuric acid, forming iron(III) sulphate, sulphur dioxide gas, and water.
189
How does iron react with dilute hydrochloric acid and dilute sulphuric acid?
- Iron readily reacts with both dilute hydrochloric acid and dilute sulphuric acid, forming iron(II) salts and releasing hydrogen gas.
190
How does concentrated nitric acid affect iron?
- Concentrated nitric acid renders iron passive due to the formation of a thin layer of iron(II,III) oxide.
191
Describe the reaction of hot iron with dry chlorine gas.
- Hot iron vigorously combines with dry chlorine gas, forming iron(III) chloride, a black solid.
192
What is formed when iron reacts with dry hydrogen chloride gas?
- Iron reacts with dry hydrogen chloride gas to form anhydrous iron(II) chloride, a white solid, and hydrogen gas.
193
What occurs when a mixture of iron filings and sulphur powder is heated?
- The mixture glows in an exothermic reaction, forming iron(II) sulphide, a black/grey solid.
194
How does pure iron react with cold pure water?
- Pure iron has no action on cold pure water.
195
Describe the reaction of iron with steam at red heat.
- At red heat, iron reacts with steam in a reversible reaction, forming tri-iron tetraoxide.
196
Explain the process of rusting of iron.
- When iron is in contact with water and air, it exhibits areas of lower oxygen concentration (anode) and areas of high oxygen concentration (cathode). Rusting involves a series of reactions resulting in the formation of hydrated iron(III) oxide, or rust.
197
When is rusting accelerated, and what slows it down?
- Rusting is accelerated by the presence of a strong electrolyte (except alkalis) in the water, while alkalis slow down rusting due to the common ion effect of the hydroxide ions, which limits the formation of hydroxide ions at the cathode and effectively reduces the electron flow from the anode to the cathode.
198
Describe the electrochemical cell involved in rusting.
- In the electrochemical cell involved in rusting, oxygen accepts electrons from iron forming iron(II) hydroxide. Additionally, alkalis contribute to the common ion effect by converting into sodium ions and hydroxide ions.
199
How can rusting (corrosion of iron) be prevented using zinc-coated iron?
- Zinc-coated iron (Galvanized iron) prevents rusting by coating iron with a layer of zinc. Zinc acts as the anode and iron as the cathode. Even if the zinc coating is scratched, the iron does not rust.
200
How does tin-coated iron prevent rusting?
- Tin-coated iron prevents rusting by corroding (rusting) when the tin coating is scratched. Tin acts as the cathode, while iron acts as the anode.
201
How is sacrificial protection implemented?
Blocks of a more reactive metal, such as zinc or magnesium, are fastened onto the iron.
202
Why does sacrificial protection work?
Zinc (or magnesium), being more reactive than iron, is oxidized and corroded in preference to iron by losing electrons.
203
What are the properties of iron(II) oxide?
Iron(II) oxide (FeO) is a black solid prepared by heating iron(II) oxalate in the absence of air. It is basic and readily dissolves in dilute mineral acids forming an iron(II) salt and water.
204
How is iron(II) oxide prepared?
Iron(II) oxide is prepared by heating iron(II) oxalate in the absence of air.
205
What happens to iron(II) hydroxide upon prolonged standing?
Iron(II) hydroxide is oxidized to hydrated iron(III) oxide, a brown solid.
206
How is iron(II) hydroxide prepared?
Iron(II) hydroxide is prepared as a green gelatinous solid precipitate by adding aqueous sodium hydroxide to an aqueous solution of iron (II) ions.
207
What are the properties of iron(II) sulphate?
Iron(II) sulphate exists as green crystals and is readily oxidized by air and other oxidizing agents to iron(III), particularly in neutral or alkaline conditions.
208
How is iron(II) sulphate prepared?
Iron(II) sulphate is prepared by reacting excess iron filings with dilute sulphuric acid, forming iron(II) sulphate and hydrogen gas. The excess iron is filtered off leaving behind a green filtrate iron(II) sulphate which is concentrated by evaporation and then allowed to cool forming green crystals.
209
How is anhydrous Iron(II) fluoride (FeF2) prepared?
It is prepared by heating iron in a stream of dry hydrogen fluoride gas.
Fe(s) + 2HF(g) → FeF2(s) + H2(g)
210
How is anhydrous Iron(II) chloride (FeCl2) prepared?
It is a white solid prepared by heating iron in a stream of dry hydrogen chloride gas.
Fe(s) + 2HCl(g) → FeCl2(s) + H2(g)
211
What is the preparation method for anhydrous Iron(II) bromide (FeBr2)?
It is prepared by heating excess iron in a stream of bromine gas to avoid oxidation of iron(II) bromide to iron (III) bromide by excess bromine.
Fe(s) + Br2(g) → FeBr2(s)
212
How is anhydrous Iron(II) iodide (FeI2) obtained?
It is prepared by heating iron in a stream of iodine vapour.
Fe(s) + I2(g) → FeI2(s)
213
How is Ammonium ferrous sulphate ((NH4)2SO4.FeSO4.6H2O) prepared?
It is a double salt prepared by crystallization of a solution containing equivalent amounts of ammonium sulphate and iron (II) sulphate.
214
What is the preparation method for Iron(II) carbonate (FeCO3)?
It is prepared by reacting an aqueous solution of an iron II) salt with aqueous sodium carbonate.
Fe2+(aq) + CO32-(aq) → FeCO3(s)
215
How can iron(II) ions in aqueous solution be detected with aqueous sodium hydroxide or aqueous ammonia solution?
Observation for both: A green precipitate insoluble in excess NaOH
216
How can iron(II) ions in aqueous solution be detected with aqueous potassium hexacynoferrate(III) solution?
Observation: A dark-blue precipitate is formed.
3Fe2+(aq) + 2[Fe(CN)6]3-(aq) → Fe3[Fe(CN)6]2(s)
217
What are the properties and preparation methods of Iron(III) oxide (Fe2O3)?
It occurs naturally as haematite and is a brown solid prepared by heating iron (III) hydroxide or iron (II) sulphate.
218
What are the properties and preparation methods of Tiri-irontetraoxide (Fe3O4)?
It occurs naturally as magnetite and is a black oxide prepared by burning iron in oxygen or by passing steam over hot iron.
219
How is Iron(III) chloride (FeCl3) prepared?
It is a dark-red/black covalent solid prepared by heating iron powder in a stream of dry chlorine gas.
2Fe(s) + 3Cl2(g) → 2FeCl3(s)
220
How does FeBr3 behave compared to FeCl3?
FeBr3 is prepared and reacts similarly to FeCl3.
221
Why are iron(III) salts acidic in aqueous solutions?
Due to its high charge density and polarizing power, the iron(III) ion strongly attracts water molecules, forming a soluble complex of hexaaquairon(III) [Fe(H2O)6]3+.
This weakens the oxygen-hydrogen bond of the water molecule in the complex, releasing hydrogen ions, which make the solution acidic.
222
What occurs when aqueous sodium carbonate is added to an aqueous solution of iron(III) ions?
A brown precipitate insoluble in excess is formed. The brown precipitate is iron(III) hydroxide, and effervescence of a colorless gas occurs, which is carbon dioxide. The iron(III) ions combine with carbonate ions forming iron(III) carbonate.
223
What happens when iron(II) is oxidized by iron(III) using chlorine gas?
2Fe2+(aq) + Cl2(g) → 2Fe3+(aq) + 2Cl−(aq). The solution changes from green to yellow/brown.
224
How does iron(II) oxidize to iron(III) using hot concentrated nitric acid?
3Fe2+(aq) + 4H+(aq) + NO3−(aq) → 3Fe3+(aq) + NO2(g) + 2H2O(l).
The solution changes from green to brown, and brown fumes of nitrogen dioxide are formed.
225
How does iron(II) oxidize to iron(III) using hydrogen peroxide in acidic conditions?
The solution changes from green to brown. The reaction is represented as: 2Fe2+(aq) + 2H+(aq) + H2O2(aq) → 2Fe3+(aq) + 2H2O(l).
226
What happens when iron(II) is oxidized by iron(III) using acidified potassium manganate(VII)?
The purple color of potassium manganate(VII) is discharged. The equation for the reaction is: MnO−(aq) + 5Fe2+(aq) + 8H+(aq) → Mn2+(aq) + 5Fe3+(aq) + 4H2O(l).
227
How does iron(II) oxidize to iron(III) using acidified potassium dichromate(VI)?
The orange color of potassium dichromate(VI) changes to green. The reaction equation is: Cr2O72−(aq) + 6Fe2+(aq) + 14H+(aq) → 2Cr3+(aq) + 6Fe3+(aq) + 7H2O(l).
228
What's the observation when iron(III) is converted to iron(II) using zinc powder?
The solution changes from yellow to green. The reaction is: Zn(s) + 2Fe3+(aq) → Zn2+(aq) + 2Fe2+(aq).
229
How is iron(III) detected in aqueous solution using aqueous sodium hydroxide or aqueous ammonia solution?
A brown precipitate forms, insoluble in excess.
230
How does iron(III) reduce to iron(II) using hydrogen sulphide?
The solution changes from yellow to green, and a yellow precipitate of sulfur forms. The reaction equation is: 2Fe3+(aq) + H2S(g) → 2Fe2+(aq) + S(s) + 2H+(aq).
231
What happens when iron(III) reduces to iron(II) using sulphur dioxide?
The solution changes from yellow to green. The reaction equation is: 2Fe3+(aq) + SO2(g) + 2H2O(l) → 2Fe2+(aq) + SO42−(aq) + 4H+(aq).
232
How does iron(III) reduce to iron(II) with potassium iodide solution?
The solution changes from yellow to green. The reaction equation is: 2Fe3+(aq) + 2I−(aq) → 2Fe2+(aq) + I2(aq).
233
How does cobalt react with air/oxygen?
At room temperature, cobalt isn't affected by air/oxygen, but on strong heating, it reacts with oxygen to form tri-cobalt tetra oxide.
The reaction equation is: 3Co(s) + 2O2(g) → Co3O4(s).
234
What are the reactions of cobalt with acids?
Cobalt reacts slowly with dilute hydrochloric and dilute sulfuric acid but more readily with concentrated acids, forming cobalt (II) salts and hydrogen gas.
The equation is: Co(s) + 2H+(aq) → Co2+(aq) + H2(g).
It's attacked more rapidly by dilute nitric acid, forming a mixture of products, and rendered passive by concentrated nitric acid.
235
How does finely divided cobalt react with carbon monoxide?
Finely divided cobalt reacts with carbon monoxide at high temperature and pressure to form a carbonyl compound, Co2(CO)8 – an orange-colored solid.
236
What are the oxidation states in which cobalt forms compounds?
Cobalt forms compounds in the +2 (most stable) and +3 oxidation states.
237
Describe cobalt(II) oxide and its reactions.
Cobalt(II) oxide is a green solid prepared by heating cobalt (II) carbonate or cobalt (II) nitrate strongly in the absence of air. It's basic and reacts with acids to form pink solutions of cobalt(II) salts and water. In the presence of air, it combines with oxygen to form tri-cobalt tetraoxide.
238
Explain cobalt(II) hydroxide and its preparation.
Cobalt(II) hydroxide is a blue solid prepared by precipitation, reacting an aqueous solution of a cobalt (II) salt with aqueous sodium hydroxide. The precipitate slowly turns pink on standing.
239
Describe cobalt(II) sulphide and its preparation.
Cobalt(II) sulphide is a black solid prepared by precipitation, bubbling hydrogen sulphide gas through an aqueous solution of a cobalt (II) salt.
240
Discuss cobalt(II) chloride, including its preparation and properties.
Cobalt(II) chloride is a red crystalline solid prepared by reacting dilute hydrochloric acid with excess cobalt(II) carbonate or excess cobalt (II) oxide.
It forms a pink filtrate and red crystals when concentrated.
Heating the red crystals removes water of crystallization, forming a blue solid.
Adding concentrated hydrochloric acid deepens the pink color, eventually becoming deep-blue.
Adding water restores the pink color as equilibrium shifts from right to left.
241
How can cobalt(II) ions in aqueous solution be detected with aqueous sodium hydroxide?
When aqueous sodium hydroxide is added, a blue precipitate forms, insoluble in excess, which turns pink on standing.
The equation is: Co(aq) + 2OH-(aq) → Co(OH)2(s).
242
What happens when aqueous ammonia is added to a solution containing cobalt(II) ions?
A blue precipitate forms, insoluble in excess, which turns red on standing. The equation is:
Co(aq) + 2OH-(aq) → Co(OH)2(s).
243
How can cobalt(II) ions be detected with potassium thiocyanate solution?
A blue solution is formed when potassium thiocyanate solution is added to the cobalt(II) ions.
244
Discuss cobalt(III) compounds and their isomers.
Cobalt (III) compounds are powerful oxidizing agents and very unstable unless complexed by suitable ligands.
In the presence of ligands like CN- or NH3, Co2+ ions are oxidized to Co3+.
Isomers of CoCl3 (NH3)6 crystallize out of solution in four different forms, distinguished by their color and the number of free Cl- ions.
These isomers can be distinguished by titrating with silver nitrate solution to find the number of moles of silver chloride precipitated per mole of the isomer. For example, one mole of Co(NH3)63+ precipitates three moles of silver chloride when titrated with silver nitrate solution, while one mole of cis and trans isomers Co(NH3)4Cl2+ precipitates one mole of silver chloride when titrated with silver nitrate solution.
245
How does nickel react with oxygen when strongly heated?
Nickel reacts with oxygen to form nickel(II) oxide, a green solid. The equation is: 2Ni(s) + O2(g) → 2NiO(s).
246
What happens when nickel reacts with water?
Nickel reacts with steam to liberate hydrogen gas and form a green residue of nickel(II) oxide. The equation is: Ni(s) + H2O(g) → NiO(s) + H2(g).
247
How does nickel react with dilute acids?
Nickel reacts with dilute hydrochloric and cold dilute sulphuric acid to form a green solution containing a nickel(II) salt and liberating hydrogen gas. The equation is: Ni(s) + 2H+(aq) → Ni2+(aq) + H2(g).
248
Discuss the reaction of nickel with chlorine.
When heated in a stream of dry chlorine, nickel forms nickel(II) chloride. The equation is: Ni(s) + Cl2(g) → NiCl2(s).
249
What happens when nickel reacts with carbon monoxide?
When heated in a stream of carbon monoxide gas to about 60°C, nickel forms a volatile liquid, nickel carbonyl, Ni(CO)4 – a complex.
The complex decomposes if the temperature is raised to about 200°C, back to nickel and carbon monoxide.
The equation is: Ni(s) + 4CO(g) → Ni(CO)4(l) at 60°C, and the reverse reaction at 200°C.
250
How does nickel(II) oxide, NiO, form?
Nickel(II) oxide is a green solid prepared by heating nickel(II) carbonate or nickel(II) nitrate. The equations are: NiCO3(s) → NiO(s) + CO2(g) and 2Ni(NO3)2(s) → 2NiO(s) + 4NO2(g) + O2(g).
251
Describe the preparation of nickel(II) hydroxide, Ni(OH)2.
Nickel(II) hydroxide is a green solid prepared by precipitation by reacting an aqueous solution of a nickel(II) salt with aqueous sodium hydroxide. The equation is: Ni2+(aq) + 2OH-(aq) → Ni(OH)2(s).
252
How is nickel(II) sulphide, NiS, obtained?
Nickel(II) sulphide is a black solid prepared by precipitation when hydrogen sulphide gas is bubbled through an aqueous solution of a nickel(II) salt. The equation is: Ni2+(aq) + S2-(aq) → NiS(s).
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How are nickel(II) ions detected in aqueous solution?
Nickel(II) ions in aqueous solution can be detected:
- With aqueous sodium hydroxide: A green precipitate forms, insoluble in excess. The equation is: Ni2+(aq) + 2OH-(aq) → Ni(OH)2(s).
- With aqueous ammonia: A green precipitate forms, soluble in excess, forming a pale blue solution. The equation is: Ni2+(aq) + 2OH-(aq) → Ni(OH)2(s), and then Ni(OH)2(s) + 6NH3(aq) → [Ni(NH3)6]2+(aq) + 2OH-(aq).
- With dimethyl glyoxime in alkaline conditions: A red precipitate forms.
254
How is copper extracted from copper pyrite?
- Concentration of the ore by froth floatation: The ore is concentrated by froth floatation to remove earthly impurities. During this process, the finely ground ore is mixed with water containing a frothing agent, and air is blown through the mixture. The pyrite floats on the surface and is skimmed off, filtered, and dried.
- Roasting: The concentrated ore is roasted in a limited air supply, forming copper(I) sulphide, iron(II) oxide, and sulphur dioxide. The equation is: 2CuFeS2(s) + 4O2(g) → Cu2S(s) + 2FeO(s) + 3SO2(g).
- Smelting: Sand (silicon(IV) oxide) is added to the product, and the mixture is heated in the absence of air. This converts iron(II) oxide to iron(II) silicate (slag), which is removed. The equation is: FeO(s) + SiO2(g) → FeSiO3(l).
- Conversion to blister copper: The copper(I) sulphide is heated in limited air, forming copper and sulphur dioxide. The equation is: Cu2S(s) + O2(g) → 2Cu(l) + SO2(g). The molten copper is cooled to form blister copper.
- Refining blister copper: Blister copper is refined by electrolysis, with impure copper as the anode, pure copper as the cathode, and copper(II) sulphate as the electrolyte. At the anode, impure copper dissolves to form copper(II) ions (Cu(s) → Cu2+(aq) + 2e-), while at the cathode, copper ions gain electrons and deposit as pure copper.
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What are the physical properties of copper?
- Copper is a brown solid with a density of 8.92 g/cm³ and melts at 1083 K.
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Discuss the chemical properties of copper.
- Copper is the reactive element in the first series of d-block elements.
It is not attacked by water, dilute sulphuric acid, or dilute hydrochloric acid, and it does not react with dry air at ordinary temperature and pressure.
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How does copper react with air or oxygen?
- Copper slowly reacts with moist air to form a green layer of basic copper(II) carbonate. When heated to 300°C, it reacts with air/oxygen to form copper(II) oxide (2Cu(s) + O2(g) → 2CuO(s)). At temperatures of 1000°C, copper(II) oxide decomposes into copper(I) oxide and oxygen (4CuO(s) → 2Cu2O(s) + O2(g)).
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What are the properties and reactions of copper(II) oxide?
Copper(II) oxide is a black solid insoluble in water, prepared by heating copper(II) carbonate or copper(II) nitrate.
It reacts with acids to form salts and water.
When heated in a stream of hydrogen gas, ammonia gas, or carbon monoxide gas, it is reduced to copper.
At about 800°C, it decomposes into copper(I) oxide and oxygen gas.
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How is copper(II) hydroxide synthesized and what reactions does it undergo?
Copper(II) hydroxide is a pale-blue solid prepared by precipitation with aqueous sodium hydroxide.
It reacts with acids to form salts and water, and it dissolves in excess ammonia to form a deep-blue solution containing tetraammine copper(II) ions.
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What are the properties and reactions of copper(II) chloride?
Anhydrous copper(II) chloride is a dark-brown solid prepared by heating copper in a stream of dry chlorine gas.
The hydrated salt, CuCl2.2H2O, is a green solid formed by reacting excess copper(II) oxide with warm dilute hydrochloric acid. It dissolves in water to form a blue solution containing [Cu(H2O)4]2+ ions, which changes color upon addition of concentrated hydrochloric acid.
The solution changes from blue to green and finally to yellow due to successive replacement of water molecules in [Cu(H2O)4]2+ by chloride ions until tetrachlorocuprate(II) is formed.
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How is copper(II) sulphide synthesized?
Copper(II) sulphide is a black solid prepared by precipitation with hydrogen sulphide gas through an aqueous solution of a copper(II) salt.
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What are the properties and reactions of copper(II) sulphate?
Copper(II) sulphate is a blue crystalline solid prepared by reacting dilute sulphuric acid with excess copper(II) carbonate or copper(II) oxide.
Upon heating, it loses its water of crystallization to form anhydrous copper(II) sulphate.
Further strong heating leads to decomposition into copper(II) oxide and sulphur trioxide gas.
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How can copper(II) ions in aqueous solution be detected?
With aqueous sodium hydroxide:
Observation: A pale-blue precipitate forms, insoluble in excess.
Equation: Cu2+(aq) + 2OH−(aq) → Cu(OH)2(s)
Upon heating, the precipitate turns black due to the formation of copper(II) oxide:
Cu(OH)2(s) → CuO(s) + H2O(l)
With aqueous ammonia:
Observation: A pale-blue precipitate forms, soluble in excess, resulting in a deep-blue solution.
Equation: Cu2+(aq) + 2OH−(aq) → Cu(OH)2(s)
Cu(OH)2(s) + 4NH3(aq) → [Cu(NH3)4]2+(aq) + 2OH−(aq)
With aqueous potassium hexacyanoferrate(II):
Observation: A red-brown precipitate is formed.
Equation: 4Cu2+(aq) + 2[Fe(CN)6]4−(aq) → Cu4[Fe(CN)6]2(s)
The precipitate dissolves in ammonia.
With aqueous potassium iodide:
Observation: A white precipitate and brown solution are formed.
Equation: 2Cu2+(aq) + 4I−(aq) → 2CuI(s) + I2(aq)
Upon addition of sodium thiosulphate, the brown color of iodine is discharged, leaving behind a clear-white precipitate:
I−(aq) + 2S2O32−(aq) → S4O62−(aq) + 2I−(aq)
264
Why is zinc referred to as a non-transition metal?
Zinc is referred to as a non-transition metal due to several reasons:
- It forms colorless compounds in the aqueous state.
- It exhibits only one oxidation state, +2.
- It is not paramagnetic.
- It does not act as a catalyst or has limited catalytic activity.
However, like other transition elements, zinc can form complexes.
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What are some ores of zinc?
Zinc occurs naturally in ores such as zinc blend (zinc sulphide), contaminated with lead(II) sulphide, and calamine (calcium carbonate), CaCO3.
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How is zinc extracted from zinc blende?
1. **Concentration of the ore by froth flotation:**
- Zinc blende is crushed into powder and mixed with water containing a frothing agent.
- Air is bubbled through the mixture, causing the low-density ore to float as froth, which is skimmed off.
2. **Roasting:**
- The concentrated ore is roasted to form zinc oxide.
- Equation: 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g)
3. **Reduction of the oxide:**
- Zinc oxide is mixed with coke and limestone in a blast furnace.
- The oxide is reduced to zinc metal by carbon dioxide.
- Equation: ZnO(s) + CO(g) → Zn(g) + CO2(g)
- The zinc metal distills off with other blast furnace gases.
- The mixture of gases is allowed to cool, and the pure zinc is separated from impurities by fractional distillation.
- Major impurities include lead(II) sulphide, cadmium, and iron.
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How does zinc react in oxygen?
- **Oxygen gas:** Zinc burns in oxygen to form zinc oxide.
- Equation: 2Zn(s) + O2(g) → 2ZnO(s)
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How does zinc react with steam?
- **Steam:** Reacts with heated zinc to form zinc oxide and hydrogen gas.
- Equation: Zn(s) + H2O(g) → ZnO(s) + H2(g)
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How does zinc react with dilute mineral acids?
- **Dilute mineral acids:** React readily with zinc to liberate hydrogen gas.
- Equation: Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)
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How does zinc react with hot concentrated sulphuric acid?
- **Hot concentrated sulphuric acid:** Oxidizes zinc to zinc sulphate and reduces the acid to sulphur dioxide.
- Equation: Zn(s) + 2H2SO4(aq) → ZnSO4(aq) + 2SO2(g) + 2H2O(l)
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How does zinc react with sodium hydroxide?
- **Aqueous sodium hydroxide:** Reacts with zinc to form a soluble complex of sodium zincate and hydrogen gas.
- Equation: Zn(s) + 2OH-(aq) + H2O(l) → [Zn(OH)4]2-(aq) + H2(g)
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How does zinc react with copper(II) sulphate?
- **Reduction of copper(II) sulphate:** Zinc reduces blue aqueous copper(II) sulphate to copper metal, forming a brown residue, and itself oxidizes to zinc sulphate solution.
- Equation: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
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How does zinc react with nitrate ions in the presence of aqueous sodium hydroxide?
Forms a colorless solution consisting of a soluble complex of sodium zincate and effervescence of a colorless gas (ammonia gas).
- Equation: 8Zn(s) + 2NO3-(aq) + 14OH-(aq) + 12H2O(l) → 8[Zn(OH)4]2-(aq) + 2NH3(g)
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What is the chemical formula of zinc oxide?
ZnO
275
Describe the reaction of zinc oxide with dilute acids.
Zinc oxide reacts with dilute acids to form zinc salts and hydrogen gas. The equation is: ZnO(s) + 2H+(aq) → Zn2+(aq) + H2(g)
276
How does zinc hydroxide react with dilute acids?
Zinc hydroxide reacts with dilute acids to produce zinc salts and water. The equation is: Zn(OH)2(s) + 2H+(aq) → Zn2+(aq) + 2H2O(l)
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What complex is formed when zinc reacts with hot concentrated sodium hydroxide?
Zinc forms a soluble complex of sodium zincate, represented as [Zn(OH)4]^2−.
278
Describe the reaction between zinc hydroxide and aqueous ammonia.
Zinc hydroxide dissolves in aqueous ammonia to form a colorless solution consisting of a soluble complex of tetraamminezinc ion.
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How can zinc ions be detected with sodium hydroxide solution?
Zinc ions form a white precipitate, which is soluble in excess alkali to form a colorless solution.
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What happens when zinc ions react with ammonia solution?
Zinc ions form a white precipitate, which is soluble in excess ammonia to form a colorless solution.
281
What happens when zinc ions react with ammonia solution?
Zinc ions form a white precipitate, which is soluble in excess ammonia to form a colorless solution.
282
What confirmatory test can be used to detect zinc ions?
Zinc ions form a yellow-white precipitate, which is soluble in ammonia, when reacted with potassium hexacyanoferrate(II) solution.
283
What is observed when to the yellow solution of chromate(VI) ions is added dilute sulphuric acid or dilute
hydrochloric acid?
An orange solution is formed.
2𝐶𝑟𝑂 2−(𝑎𝑞) + 2𝐻+(𝑎𝑞) ⇌ 𝐶𝑟 𝑂 2−(𝑎𝑞) + 𝐻 𝑂(𝑙)
284
What is observed when to the yellow solution of chromate(VI) ions is reacted with aqueous ammonia? Explain.
Observation: A green precipitate soluble in excess forming a violet solution.
Explanation: The green precipitate is chromium(III) hydroxide which is insoluble in water.
𝐶𝑟 (𝑎𝑞) + 3𝑂𝐻(𝑎𝑞) → 𝐶𝑟(𝑂𝐻)3(𝑠)
The chromium(III) hydroxide reacts with excess ammonia solution forming a soluble complex of hexaamminechromium(III) ions.
3+ ̅ 𝐶𝑟(𝑂𝐻)3(𝑠) + 6𝑁𝐻3(𝑎𝑞) → [𝐶𝑟(𝑁𝐻3)6] (𝑎𝑞) + 3𝑂𝐻(𝑎𝑞)
285
What color is Chromium(VI) oxide, CrO3?
It is a dark-red crystalline solid
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How is Chromium(VI) oxide formed?
When a saturated solution of potassium dichromate(VI) is acidified by concentrated sulphuric acid and cooled.
Cr O 2− (aq) + 2H+ (aq) → 2CrO (s) + H O(l) 2732
The crystals are filtered using glass wool not paper because the acid would attack the paper.
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How does copper react with water?
Copper does not react with pure water in any form.
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What are the reactions of copper with dilute acids?
With dilute nitric acid, copper reacts slowly to form copper(II) nitrate, nitrogen monoxide, and water. However, copper is not affected by dilute sulphuric acid or dilute hydrochloric acid.
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How does copper react with concentrated acids?
Hot concentrated sulphuric acid leads to the formation of copper(II) sulphate, sulphur dioxide, and water.
Boiling concentrated hydrochloric acid results in a complex of dichlorocuprate(I) and hydrogen gas.
Concentrated nitric acid produces copper(II) nitrate, nitrogen dioxide, and water.
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What happens when copper reacts with halogens?
Fluorine, chlorine, and bromine react with hot copper to form the corresponding copper(II) halides. With iodine, copper(I) iodide is formed because iodine is not oxidizing enough to convert copper to copper(II) iodide.
291
What are some compounds of copper in the +1 oxidation state?
Copper(I) compounds are unstable in aqueous solution and undergo disproportionation into copper metal and copper(II) ions.
Examples include copper(I) oxide (Cu2O), copper(I) chloride (CuCl), and copper(I) iodide (CuI).
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How does copper(I) oxide react with dilute sulphuric acid?
Copper(I) oxide reacts with warm dilute sulphuric acid to disproportionates into copper, copper(II) sulphate, and water.
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What are the properties and reactions of copper(I) chloride?
Copper(I) chloride is a white solid prepared by reduction when a mixture of copper(II) chloride, excess copper, and concentrated hydrochloric acid is heated.
It's insoluble in water but dissolves in concentrated hydrochloric acid forming a dichlorocuprate(I) complex.
It also dissolves in ammonia forming a complex of diamminecopper(I) chloride.
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How is copper(I) iodide synthesized?
Copper(I) iodide is a white solid precipitated by reacting aqueous copper(II) sulphate with aqueous potassium iodide.
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How do copper(II) salts behave in aqueous solution?
Aqueous solutions of copper(II) salts are blue due to the presence of a soluble complex of tetraquacopper(II) ions, [Cu(H2O)4]2+.
The solution is weakly acidic because the hydrated ions undergo hydrolysis with water, producing hydronium ions.
