Chapter 8 Reactivity Trends

Question 1

Group 2 metal + water

Answer 1

Metal hydroxide + hydrogen

Question 2

Why does reactivity increase as you go down Group 2

Answer 2

• Group 2 experience 2 ionisation energies: 1st and 2nd ionisation energies
• The ionisation energies decrease as you go down the group because attraction between the nucleus and outer electrons decreases due to increasing atomic radius and increased shielding

Question 3

Solubility of Group 2 metal hydroxides in water

Answer 3

Increases as you go down the group -> so the resulting solutions contain more OH- ions

This can be proven by measuring the pH of the solutions

Question 4

Uses of Group 2 compounds as bases

Answer 4

• Calcium hydroxide is added to fields -> to increase pH of acidic soils
• Magnesium and calcium carbonates are used as antacids in treating acid ingestion

Question 5

Group 7 - Halogens

Answer 5

• Most reactive non-metallic group
• Occur as stable halide ions dissolved in sea water

Question 6

Group 7: Trend in boiling points

Answer 6

• Increases as you go down the group
• more electrons
• so stronger london forces
• so more energy needed to overcome these forces
• so boiling point increases

Question 7

Halogen-halide displacement reactions

Answer 7

If the halogen is more reactive than the halide in the solution, it will displace it

Question 8

How to tell the difference between iodine and bromine in water (they look very similar orange-brown colour)

Answer 8

Add cyclohexane and shake

• iodine goes deep violet
• bromine stays orange

Question 9

Colours of the halogens

Answer 9

Fluorine: pale yellow gas
Chlorine: pale green gas
Bromine: red-brown liquid
Iodine: shiny grey-black solid

Question 10

Group 7: Trend in reactivity

Answer 10

• Atomic radius increases
• More inner shells so shielding increases
• Less nuclear attraction to capture an electron from another species
• Reactivity decreases

Question 11

Disproportionation

Answer 11

A redox reaction in which the same element is both oxidised and reduced

Question 12

Examples of disproportionation reactions

Answer 12

Chlorine + water
Chlorine + dilute sodium hydroxide

Question 13

Chlorine + water

Answer 13

Cl2 + H2O -> HClO + HCl

Question 14

HClO

Answer 14

chloric acid

Question 15

Uses of chloric acid

Answer 15

Weak bleach

Question 16

Chlorine + sodium hydroxide

Answer 16

NaClO + NaCl + H2O

Question 17

NaClO

Answer 17

Sodium chlorate

Question 18

Benefits of chlorine

Answer 18

Cleaning water (kills bacteria)

Question 19

Risks of chlorine

Answer 19

• Toxic gas
• Can react with organic hydrocarbons -> forms chlorinated hydrocarbons which cause cancer

Question 20

Tests for anions

Answer 20

• Carbonate ions
• Sulfate ions
• Halide ions

Question 21

Test for carbonate ions

Answer 21

1. Add dilute nitric acid
2. If bubbles are seen, it is a carbonate
3. To test the gas for CO2, bubble through limewater and if it goes cloudy its CO2

Question 22

Limewater

Answer 22

Calcium hydroxide

Question 23

Test for sulfates

Answer 23

1. Add barium nitrate or barium chloride
2. White precipitate of barium sulfate formed if sulfate is present

Question 24

When to use barium chloride or barium nitrate in sulfate test

Answer 24

If doing a halide test afterwards, use barium nitrate to avoid introducing chloride ions

Question 25

Test for halides

Answer 25

1. Add silver nitrate

Question 26

Tesy for NH4+

Answer 26

1. Add NaOH to a solution containing an ammonium ion
2. Ammonia gas is. produced
3. Warm and test with moist red litmus paper, it will go blue