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Chemistry - Module 3 > Chapter 8 - Reactivity Trends > Flashcards

Chapter 8 - Reactivity Trends Flashcards

1
Q

What are group 2 metals also known as

A

Alkali earth metals

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2
Q

Why is it called group 2 metals

A

Two electrons in their outermost shell in the S sub shell

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3
Q

What kind of agents are group 2 elements

A

Reducing agents

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4
Q

How does reactivity change does group 2

A

Increases

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5
Q

Why does reactivity increase down group 2

A

o As the atomic radii increase there is more shielding
o The nuclear attraction decreases and it is easier to remove outer electrons
o Cations form more easily

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6
Q

How does group two elements react with oxygen

A

2M (s) + O2 (g) → 2MO (s)

• Where M is any metal in group 2

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7
Q

2M (s) + O2 (g) → 2MO (s)

What is oxides and what is reduced

A

• Redox = M = oxidised + O = reduced

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8
Q

Observations when magnesium reacts with oxygen

A

• Magnesium with oxygen in air burns with a brilliant white light and forms white magnesium oxide

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9
Q

How does group two metals react with water

A

M (s) + 2H2O (l) → M(OH)2 (s) + H2 (g)

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10
Q

What is oxides and reduced in

M (s) + 2H2O (l) → M(OH)2 (s) + H2 (g)

A

• Redox = M = oxidised + H = reduced (forms alkaline hydroxides)

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11
Q

How do group two elements react with dilute acids

A

M (s) + 2HCl (aq) → MCl2 (aq) + H2 (g)

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12
Q

What is oxides and what is reduced

M (s) + 2HCl (aq) → MCl2 (aq) + H2 (g)

A

• Redox = M = oxidised + H = reduced

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13
Q

How do you form 2+ ions in terms of ionisation energy

A

• The formation of +2 ions from gaseous atoms requires two ionisation energies

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14
Q

What are the two ionisation energies dir group 2 elements

A

M(g) → M+(g) + e-

M+(g) → M2+(g) + e-

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15
Q

Do the first and second ionisation energy decrease or increase down the group

A

Decrease

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16
Q

Why do the first and second ionisation energies decrease down the group

A

o The attraction between the nucleus and outer electrons decreases
o Atomic radius increases, and there is increased shielding
o Group 2 elements because more reactive and stronger reducing agents down group.

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17
Q

How do group two oxides react with water

A

releasing hydroxide ions, to form alkaline solutions:

CaO (s) + H2O (l) → Ca2+ (aq) + 2OH- (aq)

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18
Q

Do group two solutions get more or less alkaline down the group

A

solutions get more alkaline going down the group

o This is due to increasing solubility meaning the resulting solutions formed contain more OH- ions

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19
Q

Does solubility increase or decrease down group 2

A

Increase

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20
Q

What happens when a group 2 solution becomes saturated after its oxide reacted with water

A

• When the solution becomes saturated any further metal and hydroxide ions will form a precipitate:

Ca2+ (aq) + 2OH- (aq) → Ca(OH)2 (s)

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21
Q

Example of differences in pH

A

• Solid magnesium hydroxide, Mg(OH)2 (s), is only slightly soluble in water

o The solution has a low OH-(aq) concentration and a pH ≅ 10

• Barium hydroxide, Ba(OH)2 (s), is much more soluble in water

o The solution has a greater OH-(aq) concentration and a pH ≅ 13

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22
Q

How are group 2 compounds used in agriculture

A

alcium hydroxide, Ca(OH)2, is reasonably soluble in water and is used in agriculture to neutralise acidic soils

Ca(OH)2 (s) + 2H+ (aq) → Ca2+ (aq) + 2H2O (l)

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23
Q

How is group 2 compounds used in medicine

A

• Magnesium hydroxide, Mg(OH)2, is partially soluble in water and is used in suspension (known as ‘milk of magnesia’) to neutralise excess acid in the stomach and treat constipation

Mg(OH)2 (s) + 2HCl (aq) → MgCl2 (aq) + 2H2O (l)

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24
Q

Why is it safe to ingest magnesium hydroxide

A

only partially soluble making the solution only slightly alkaline (pH ≅ 10) due to the low OH- concentration

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25
How does boiling points change down group 7
Increases
26
Why does boiling points increase down group 7
27
Fluorine = appearance + state at RTP
Pale yellow gas
28
Chlorine = appearance + state at RTP
Pale green gas
29
Bromine = appearance + state at RTP
Red brown liquid
30
Iodine = appearance + state at RTP
Shines grey black solid
31
What kind of molecules are halogens
Diatomic
32
Does reactivity increase or decrease down group 7
Decreases
33
Why does reactivity decrease down group 7
34
How to carry out a halogen halide displacement reactions
• Solution of each halogen added to aqueous solutions of outer halides. E.g. solution of chlorine, Cl2 added to aqueous solutions containing both Br- and I- ions. • If halogen added is more reactive than halide present, a reaction will take place, the halogen displacing the halide from solution and the solution will change colour.
35
Halogen solution colours in water / aqueous solution of halides
36
What’s the problem with this displacement reaction
Solutions of iodine and bromine in water can appear a similar orange-brown colour depending on concentration
37
What should we do to fix the problem of displacement reactions
add an organic non-polar solvent like cyclohexane, and mixture should be shaken.
38
Colours of halogens in cyclohexane
39
Displacement reaction table - aqueous solution of halides
40
Displacement reaction table - organic solvent
41
What type of agent is a halogen
Oxidising agent
42
Define disproportionation
• When an ELEMENT is simultaneously reduced and oxidised in a chemical reaction
43
What chlorine used for
Water purification
44
How is chlorine used in water purification
• When small amounts of chlorine added to water, disproportionation reaction takes place = chlorine = • Chloric(I) acid (HClO) sterilises water by killing bacteria = bleach
45
How to test if HClO is bleach
• If some universal indicator is added to the solution it will first turn red due to the acidity of both reaction products. It will then turn colourless as the HClO bleaches the colour.
46
HClO (chloric acid) can further dissociate into what
ClO- (aq): HClO (aq) → H+ (aq) + ClO- (aq)
47
Why would we react chlorine with dilute aqueous sodium hydroxide instead of water
• Reaction of chlorine with water is limited by low solubility of chlorine in water – if water contains dissolved sodium hydroxide, much more chlorine dissolves and another disproportionation reaction takes place.
48
Equation for reacting chlorine with cold dilute aqueous sodium hydroxide
49
Ionic equation for formation of bleach
50
Half equations for formation of bleach
51
Benefits of chlorine use
it keeps water fit to drink and kills bacteria
52
Risks of chlorine use
extremely toxic gas. • Chlorine is a respiratory irritant in small concentrations and fatal in large concentrations.
53
Risks of chlorine use = chlorinated hydrocarbons
• Chlorine in drinking water can react with organic hydrocarbons like methane, formed from decaying vegetation. Chlorinated hydrocarbons are formed, suspected of causing canc
54
How to test for halides
• dissolving the solution in nitric acid and then adding silver nitrate solution dropwise
55
Why do you add nitric acid in a halide test
prevent any false positive results from carbonate ions precipitating out with silver ions
56
Equation for halide test
Ag+ (aq) + X- (aq) → AgX (s) (ionic equation) o Where X- is the halide ion • The state symbols are key in this equation
57
Colour of precipitate - chloride
White
58
Colour of precipitate - bromide
Cream
59
Colour of precipitate - iodide
Yellow
60
What form is the halide in when precipitated
AgBr
61
What’s the problem with the halide test
Similar colours
62
How do we fix problem with halide test
Add ammonia in follow up test = dilute then concentrated
63
Results of ammonia follow up test
• the precipitate dissolves in dilute ammonia the unknown halide is chloride • If the precipitate does not dissolve in dilute, but does dissolve in concentrated ammonia the unknown halide is bromide • If the precipitate does not dissolve in dilute or concentrated ammonia, then the known halide is iodide
64
Table - halide identification test observations = both tests = summarise
65
How to test for carbonates
Add around 1 cm3 of dilute nitric acid bung with a delivery tube should be attached to the test tube o The delivery tube should transfer the gas which is formed into a different test tube that contains a small amount of limewater (calcium hydroxide solution)
66
Results of carbonate test
• If a carbonate compound is present then effervescence should be seen and the gas produced is CO2 which forms a white precipitate of calcium carbonate when bubbled through limewater:
67
Reactions = 2 = that take place in carbonate test
68
How to test for sulphates
• Add few drops of aqueous barium chloride or barium nitrate (nitrate if carrying out a halide test after) • If sulfate present = white precipitate formed
69
Ionic equation for Sulfate test
70
Correct order of test
o Carbonate CO3 2- o Sulfate SO4 2- o Halides Cl-, Br-, I-
71
Why do we start with the carbonate test
• Neither sulfate or halide ions produce bubbles with dilute acid, it can be carried out without possibility of incorrect conclusion.
72
If there is a mixture of ions and there is no bubbles after the carbonate test - can I continue?
Yes = proceed to the next test
73
If there is a mixture of ions and there is bubbles after the carbonate test - can I continue?
Yes + No = • If bubbles = carbonate ions reacted = no more = can also move on BUT Keep adding nitric acid until no more bubbles = all carbonate reacted
74
Why do we do the sulphate test second
• Add a solution containing Ba2+ (aq) ions and looking for white precipitate BaSO4 (s) • Barium carbonate, BaCO3 is white and insoluble in water so if you carry out sulfate test on carbonate, you will also get a white precipitate. • Thus it comes second, only do it if NO carbonate present from 1st test
75
What should I do if I’m doing a halide test after my sulphate test
filter to remove barium sulphate
76
Why do we do the halide test last
• Silver carbonate Ag2 CO3 and silver nitrate Ag2 SO4, both insoluble in water and form precipitates in tests. Thus important to carry out halide test last, after carrying out carbonate and sulfate tests to rule out possibilities.
77
How to test for ammonium ions
• ammonium ions, NH4+ = by reacting with warm aqueous sodium hydroxide forming ammonia gas
78
Ionic equation for ammonium ion test
79
Results of an ammonium ion test
• Ammonia gas is produced. You are unlikely to see gas bubbles as ammonia is very soluble in water • Ammonia gas can be identified by its pungent smell or by turning red litmus paper blue

Chemistry - Module 3 (5 decks)

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