Chapter 8 - Reactivity Trends

Question 1

What is a reducing agent?

Answer 1

A species that donates its electrons to another species, thereby reducing that species

Question 2

Which group are reducing agents commonly found?

Answer 2

Group 2

Question 3

What (and why) is the trend in reactivity down group 2?

Answer 3

• Reactivity increases
• Greater atomic radius, more electron shielding, less attraction to the nucleus
• Easier to lose electrons and form bonds

Question 4

What is the general equation for a group 2 element reacted with water?

Answer 4

Metal + Water → Metal hydroxide + Hydrogen

Question 5

What is the general equation of a group 2 element reacted with oxygen?

Answer 5

Metal + Oxygen → Metal oxide

Question 6

What is the general equation for a group 2 oxide reacted with water?

Answer 6

Metal oxide + Water → Metal hydroxide

Question 7

What (and why) is the trend of solubility down group 2?

Answer 7

• Solubility increases
• Down group 2, metal ions become larger and so the attraction between ions in the solid lattice decreases
• So polar solvents can attract ions in lattice easier and dissolve the solid

Question 8

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

Answer 8

Bases

Question 9

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

Answer 9

Alkalis

Question 10

What is the use of calcium hydroxide in agriculture?

Answer 10

To increase the pH of acidic soils

Ca(OH)2 + 2[H]+ -> [Ca]2+ + 2H2O

Question 11

How are group 2 compounds used in medicine?

Answer 11

Used in indigestion tablets such as antacids, often a suspension of a metal hydroxide in water

Question 12

What is another name for group 2?

Answer 12

Alkaline Earth Metals

Question 13

What is another name for group 7?

Answer 13

Halogens

Question 14

What (and why) is the trend in boiling point down group 7?

Answer 14

• Boiling point increases
• Atomic size increases (more electrons)
• Greater ability to form London forces
• Requiring more energy to overcome and thus higher boiling points

Question 15

What (and why) is the trend in reactivity down group 7?

Answer 15

• Reactivity decreases
• Atomic size increases
• Therefore a greater effect of electron shielding and weaker nuclear attraction
• So it’s harder to gain an electron and react

Question 16

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

Answer 16

Displace them

Question 17

What can displacement reactions be used to identify?

Answer 17

Which halide is present in a solution

Question 18

What substance is used to test for halides?

Answer 18

Silver nitrate solution, AgNO3(aq)

Question 19

How can the results for a halide test be further tested?

Answer 19

• Check solubility in ammonia solution
• AgCl is soluble in dilute ammonia
• AgBr is soluble in concentrated ammonia
• AgI is insoluble in both dilute and concentrated ammonia

Question 20

What is disproportionation?

Answer 20

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

Question 21

Describe the test for carbonates:

Answer 21

• Add dilute nitric acid to the testing solution
• Effervescence indicates a possible carbonate
• To confirm, bubble the gas through lime water, to which it will turn cloudy

Question 22

Describe the test for sulfates:

Answer 22

• Add aqueous barium nitrate to the testing solution
• A white precipitate will form

Question 23

Halide test results:

Answer 23

• Chlorine - White precipitate
• Bromine - Cream precipitate
• Iodine - Yellow precipitate

Question 24

What is the correct order for anion tests?

Answer 24

• Carbonate
• Sulfate
• Halide

Question 25

Why is there a correct order for anion tests?

Answer 25

• Carbonates also form a white precipitate in the sulfate test but not vice versa • Carbonates and sulfates form precipitates with silver nitrate

Question 26

Describe the test for ammonium ions:

Answer 26

• Add aqueous sodium hydroxide to the testing solution • Ammonia gas is produced • Gas can be detected with moist indicator paper as it will turn blue (paper must be moist to form the base NH4OH)

Question 27

What are the halide solutions’ colours when added to cylcohexane?

Answer 27

• Chlorine - Pale green • Bromine - Orange • Iodine - Violet

Question 28

Table for halogen-halide displacement reactions:

Answer 28

Question 29

What is the reaction (and what type) between chlorine and cold, dilute, aqueous sodium hydroxide?

Answer 29

Cl2(aq) + 2NaOH(aq) → NaClO(aq) + NaCl(aq) + H2O(l) • Disproportionation reaction, as chlorine is both oxidised and reduced