Chapter 8 - Reactivity Trends

Question 1

What is a reducing agent?

Answer 1

A species that donates its electrons to another species, reducing it.

Question 2

Which group are reducing agents commonly found?

Answer 2

Group 2

Question 3

Explain the trend in reactivity down group 2.

Answer 3

As you go down the group, atomic radius and shielding increases, so there is less attraction and ionisation energies decrease. Therefore it’s easier to lose electrons and reactivity increases.

Question 4

What are the products of a group 2 element reacting with water?

Answer 4

Metal hydroxide + Hydrogen

Question 5

What is the product of a group 2 element reacting with oxygen?

Answer 5

Metal oxide

Question 6

Given that group 2 oxides, hydroxides and carbonates neutralise acids, what can they be referred to as?

Answer 6

Bases

Question 7

Given that most group 2 oxides, hydroxides and carbonates are soluble in water, what are they also besides bases?

Answer 7

Alkalis

Question 8

What is the use of calcium hydroxide in agriculture? Give an equation.

Answer 8

Increases pH of acidic soils.

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

Question 9

How are group 2 compounds used in medicine?

Answer 9

Used in indigestion tablets as antacids.

Question 10

What is another name for group 2?

Answer 10

Alkaline earth metals

Question 11

Explain the trend in boiling point down group 7.

Answer 11

Elements have more electrons as you go down the group, so there are increased London forces. So more energy is needed to overcome the intermolecular forces, so boiling point increases.

Question 12

Explain the trend in reactivity down group 7.

Answer 12

As you go down the group, atomic radius increases, and there are more inner shells, causing shielding to increase. This causes nuclear attraction to decrease, so it is harder to capture an electron from another species. Therefore reactivity decreases.

Question 13

What do more reacting halogens do to less reactive halide ions?

Answer 13

Displaces them

Question 14

What can displacement reactions be used to identify?

Answer 14

Which halide is present in the solution

Question 15

What compound is used to test for halides?

Answer 15

Aqueous silver nitrate

Question 16

What is disproportionation?

Answer 16

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

Question 17

Describe the test for carbonates.

Answer 17

Add unknown compound to test tube and add dilute nitric acid.
If bubbling is seen, then it is a carbonate.
To make sure, bubble the gas through limewater and it will turn milky, indicating a positive test.

Question 18

Describe the test for sulfates.

Answer 18

Add aqueous barium ions to unknown solution. If white precipitate forms, then sulfate is present.

Question 19

Describe the test for halides.

Answer 19

Add aqueous silver nitrate to solution.
Chloride - white precipitate
Bromide - cream precipitate
Iodide - yellow precipitate
To make sure, add aqueous ammonia. If insoluble, then it is iodide. If soluble, then it is chloride or bromide.

Question 20

What is the correct order for these anion halide tests?

Answer 20

Carbonate test, sulfate test, halide test

Question 21

Why is the correct order for anion tests carbonate, sulfate, halide?

Answer 21

Carbonate first because it is the only test that produces bubbles, so it can be ruled out first.

Sulfate second because carbonate will also produce white precipitate, so it needs to be done after carbonate test.

Halide last because carbonates and sulfates are both insoluble in water and will both form precipitates in this test, so they need to be ruled out first.

Question 22

Describe the test for cations (ammonium ion).

Answer 22

1. Add sodium hydroxide to solution to provide hydroxide ions.
2. Heat test tube to remove ammonia gas
3. Smell for ammonia, and red litmus paper will turn blue

Question 23

What are the benefits of chlorine use?

Answer 23

Disinfectant for water that kills all bacteria so it is safe to drink.

Question 24

What are the risks of chlorine use?

Answer 24

Respiratory irritant
Toxic gas
Can cause cancer by formation of chlorinated hydrocarbons

Question 25

What colours are the halogens in water?

Answer 25

Chlorine - pale green
Bromine - orange
Iodine - brown

Question 26

What colours are the halogens in cyclohexane?

Answer 26

Chlorine - pale green
Bromine - orange
Iodine - violet

Question 27

What is the trend in alkalinity of the solution formed when group 2 oxides are added to water?

Answer 27

Group 2 oxides react with water to form a metal hydroxide. Hydroxide ions in solution cause alkalinity.
Down group 2, solubility of the metal hydroxide increases, so pH and alkalinity also increase.