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Chemistry Module 3 - Own Flashcards > Reactivity Trends > Flashcards

Reactivity Trends Flashcards

1
Q

What are the Group 2 elements also known as?

A

They are known as the alkaline earth metals.

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2
Q

Why are Group 2 elements not found in their elemental form naturally?

A

Because they are reactive metals and occur in stable compounds like calcium carbonate (CaCO₃).

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3
Q

How many outer-shell electrons do Group 2 elements have?

A

They have two outer-shell electrons.

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4
Q

What happens to a Group 2 atom during a redox reaction?

A

It loses two electrons to form a 2+ ion, undergoing oxidation.

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5
Q

Why are Group 2 elements called reducing agents?

A

Because they lose electrons, causing another species to gain electrons (be reduced).

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6
Q

What is the general formula of metal oxides formed when Group 2 elements react with oxygen?

A

The general formula is MO, where M represents the Group 2 metal.

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7
Q

Write the balanced equation for the reaction of magnesium with oxygen.

A

2Mg(s) + O2(g)→2MgO(s)

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8
Q

What is the trend in reactivity of Group 2 elements down the group?

A

Reactivity increases down the group.

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9
Q

Why does reactivity increase down Group 2?

A

Due to decreasing ionisation energy, caused by increasing atomic radius and greater electron shielding.

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10
Q

What is the general equation for the reaction of a Group 2 metal with water?

A

M(s)+2H2O(l) → M(OH)2(aq) + H
2(g)

Metal + Water –> Salt + Hydrogen

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11
Q

Which Group 2 metals react slowly with water?

A

Magnesium and Beryllium react very slowly.

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12
Q

How does the reaction of Group 2 metals with water change down the group?

A

The reaction becomes more vigorous as reactivity increases.

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13
Q

What are the oxidation states of Sr in the reaction Sr(s) + 2H2O(l) → Sr(OH)2(aq) + H2(g)?

A

Sr goes from 0 to +2 (oxidation), H goes from +1 to 0 (reduction).

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14
Q

What is the general equation for the reaction of a Group 2 metal with a dilute acid?

A

Metal + acid → salt + hydrogen

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15
Q

Write the balanced equation for the reaction of magnesium with hydrochloric acid.

A

Mg(s) + 2HCl(aq) –> MgCl2(aq) + H2(g)

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16
Q

What are the trends in ionisation energy for Group 2 elements?

A

First and second ionisation energies decrease down the group.

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17
Q

Why does ionisation energy decrease down Group 2?

A

Because atomic radius increases and electron shielding reduces the attraction between nucleus and outer electrons.

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18
Q

How does the formation of a 2+ ion from a Group 2 metal occur?

A

First Ionisation Energy = M(g) → M+(g) + e-

Second Ionisation Energy = M+(g) → M2+(g) + e-

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19
Q

Which Group 2 element is the most reactive?

A

Barium (Ba) is the most reactive, as reactivity increases down the group.

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20
Q

What type of reaction occurs when a Group 2 metal reacts with oxygen, water, or acid?

A

A redox reaction, because the metal is oxidised and another species is reduced.

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21
Q

What is the general reaction of Group 2 oxides with water?

A

MO(s) + H2O(l) –> M2+(aq) + 2OH-(aq)

Metal Oxide + Water –> Metal + Hydroxide

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22
Q

What happens when Group 2 hydroxides dissolve in water?

A

They release OH⁻ ions, forming an alkaline solution.

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23
Q

Why does calcium hydroxide
Ca(OH)2 form a solid precipitate in water?

A

Because it has limited solubility, and when the solution is saturated, excess Ca(OH)2 precipitates as a solid.

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24
Q

What is the solubility trend of Group 2 hydroxides down the group?

A

Solubility increases, leading to more OH⁻ ions in solution and a higher pH.

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25
Compare the solubility and pH of Mg(OH)₂ and Ba(OH)₂ in water.
Mg(OH)₂ is only slightly soluble, giving a solution with low OH⁻ concentration and pH ≈ 10. Ba(OH)₂ is much more soluble, giving a solution with high OH⁻ concentration and pH ≈ 13.
26
What is the purpose of calcium hydroxide in agriculture?
It neutralises acidic soil, forming neutral water: Ca(OH)2(s) + 2H+(aq) --> Ca2+(aq + 2H2O(l)
27
How are Group 2 compounds used in medicine?
Magnesium hydroxide and calcium carbonate are used in indigestion tablets (e.g., Gaviscon, Rennie) to neutralise excess stomach acid.
28
Write the neutralisation equation for magnesium hydroxide reacting with hydrochloric acid.
Mg(OH)2(s) + 2HCl(aq) --> MgCl2(aq) + 2H2O(l)
29
Write the neutralisation equation for calcium carbonate reacting with hydrochloric acid.
CaCO3(s) + 2HCl(aq) --> CaCl2(aq) + 2H2O(l) + CO2(g)
30
What happens when a white solid appears at the bottom of a test tube containing a Group 2 hydroxide solution?
It indicates that the solution has become saturated, and excess hydroxide has precipitated.
31
What is the trend in alkalinity of Group 2 hydroxide solutions down the group?
Alkalinity increases as solubility increases, leading to higher OH⁻ concentration and higher pH.
32
What are the halogens?
The elements in Group 7 of the periodic table: fluorine (F₂), chlorine (Cl₂), bromine (Br₂), iodine (I₂), and astatine (At₂).
33
Why are halogens highly reactive?
They have 7 outer-shell electrons, so they only need to gain 1 electron to achieve a full outer shell, making them strong oxidising agents.
34
What are the physical states of the halogens at room temperature?
Fluorine (F₂): Pale yellow gas Chlorine (Cl₂): Pale green gas Bromine (Br₂): Red-brown liquid Iodine (I₂): Shiny grey-black solid
35
What is the trend in boiling points down Group 17?
Boiling points increase down the group due to: More electrons → stronger London forces More energy required to break intermolecular forces
36
What is the redox reaction of halogens when they gain electrons?
Cl2 + 2e- → 2CL- Each halogen is reduced to form a halide ion (X⁻).
37
What type of agent is a halogen in a redox reaction?
An oxidising agent because it gains electrons and causes another species to be oxidised.
38
What is a halogen-halide displacement reaction?
A more reactive halogen displaces a less reactive halide from solution.
39
What is the reactivity trend of the halogens down the group?
Reactivity decreases because: Atomic radius increases More electron shielding Weaker nuclear attraction for electrons
40
What is observed when chlorine (Cl2) is added to bromide (Br-) solution?
The solution turns orange as bromine (Br₂) is formed. Cl2 + 2Br- --> 2Cl- + Br2
41
What is observed when chlorine (Cl2) is added to iodide (I2) solution?
The solution turns violet as iodine (I₂) is formed. Cl2 + 2I- --> 2Cl- + I2
42
What happens when bromine (Br2) is added to iodide (I2) solution?
The solution turns violet as iodine (I₂) is formed. Br2 + 2I- --> 2Br- + I2
43
Does iodine (I2) react with any halide solution?
No, because iodine is the least reactive halogen.
44
What are the colour changes of halogens in water?
Cl₂ → Pale green Br₂ → Orange I₂ → Brown
45
What are the colour changes of halogens in cyclohexane?
Cl₂ → Pale green Br₂ → Orange I₂ → Violet
46
What happens when chlorine reacts with bromide ions (Br-)?
Chlorine displaces bromine in a redox reaction: Cl2 + 2Br- --> 2Cl- + Br2 Bromine is oxidized from -1 to 0 Chlorine is reduced from 0 to -1
47
What is fluorine and why is it so reactive?
Fluorine (F2) is a pale yellow gas that reacts with nearly every substance. It is the most reactive halogen due to: Small atomic radius Very high electronegativity Strong oxidising ability
48
What is astatine and why is it rare?
Astatine (At2) is a radioactive element that decays quickly, making it extremely rare. It is predicted to be the least reactive halogen.
49
What is the trend in reactivity of the halogens?
Reactivity decreases down the group because: Atomic radius increases More electron shielding Weaker nuclear attraction to capture electrons Less oxidising ability
50
What is a disproportionation reaction?
A redox reaction where the same element is both oxidised and reduced.
51
Give an example of disproportionation: Chlorine + Water
Cl2 + H2O --> HClO + HCl Chlorine (0) → -1 in HCl (Reduction) Chlorine (0) → +1 in HClO (Oxidation) HClO (chloric(I) acid) kills bacteria Used in water treatment
52
What happens when chlorine reacts with cold, dilute sodium hydroxide?
A disproportionation reaction: Cl2 + 2NaOH → NaClO + NaCl + H2O Chlorine (0) → -1 in NaCl (Reduction) Chlorine (0) → +1 in NaClO (Oxidation) NaClO (sodium chlorate(I)) is used in household bleach
53
What are the benefits of chlorine use?
Kills bacteria in drinking water Prevents diseases (e.g., typhoid, cholera)
54
What are the risks of chlorine use?
Toxic gas (respiratory irritant, fatal in high doses) Forms chlorinated hydrocarbons, possibly carcinogenic
55
How do you test for halide ions?
Using silver nitrate AgNO3: Ag+ + X- → AgC(s)
56
What coloured precipitates do Chloride, Bromide and Iodine ions form?
Chloride → White precipitate (AgCl) Bromide → Cream precipitate (AgBr) Iodide → Yellow precipitate (AgI)
57
What is qualitative analysis?
A method used to identify ions or compounds in a substance based on observations rather than numerical measurements. Observations include: ✅ Gas bubbles (effervescence) ✅ Precipitates (solid formation) ✅ Colour changes ✅ Identification of gases
58
How do you test for carbonate ions CO3(2-)?
Add dilute nitric acid (HNO₃) and observe for effervescence (bubbles). 1. If gas is produced, test for carbon dioxide by bubbling through limewater. 2. Limewater turns cloudy due to the formation of calcium carbonate CaCO3
59
What colour precipitate forms when adding CO2 and Ca(OH)2 together?
CaCO3 (white precipitate) + H2O
60
Why is the carbonate test done first?
BaCO₃ is also a white precipitate, so the carbonate test must be done first to avoid a false positive.
61
How do you test for halide ions?
Add aqueous silver nitrate (AgNO3) to the solution. If a halide is present, a silver halide precipitate forms: Chloride → White precipitate (AgCl) Bromide → Cream precipitate (AgBr) Iodide → Yellow precipitate (AgI)
62
What is the ionide equation for testing for Halide Ions?
Ag+ + X- --> AgX
63
How can you check what type of silver halide is present in a solution?
Confirm with ammonia solution: AgCl dissolves in dilute NH₃. AgBr dissolves in concentrated NH₃. AgI is insoluble in NH₃.
64
Why is the halide test done last?
Ag₂CO₃ and Ag₂SO₄ are insoluble white precipitates, so carbonate and sulfate ions must be removed first.
65
How do you test for ammonium ions (NH4+)?
Add sodium hydroxide (NaOH) and warm gently. If ammonium ions are present, ammonia gas (NH3) is released. Ammonia gas is alkaline, so it turns moist red litmus paper blue.
66
What is the reaction equation of the ammonium test?
NH4+ + OH- --> NH3 + H2O
67
What is the correct order of qualitative tests for anions and why?
1. Carbonate Test (CO₃²⁻) = Carbonates react with acids to form CO₂ gas, while sulfates and halides do not. 2. Sulfate Test (SO₄²⁻) = BaCO₃ is a white precipitate like BaSO₄, so carbonates must be removed first. 3. Halide Test (Cl⁻, Br⁻, I⁻) = Ag₂CO₃ and Ag₂SO₄ also form precipitates, which would interfere with results.
68
Why use nitric acid (HNO₃) and not HCl or H₂SO₄ in the carbonate test?
HCl contains chloride ions → gives false positive in the halide test. H₂SO₄ contains sulfate ions → gives false positive in the sulfate test.

Chemistry Module 3 - Own Flashcards (6 decks)

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