topic 8

Question 1

Explain the origin of the colours in flame tests (2)

Answer 1

Excited electrons. (1)
move down energy levels. (1)

Question 2

State what would be seen when concentrated sulfuric acid is added to separate solid samples of each of these compounds. (4)
(i) Lithium chloride
(ii) Sodium bromide
(iii) Potassium bromide

Answer 2

(i) steamy fumes
(ii) brown vapour
(iii) purple vapour.

Question 3

Explain the term oxidation in terms of electron transfer. (1)

Answer 3

loss of electrons

Question 4

Explain the term oxidising agent in terms of electron transfer

Answer 4

a substance which gains electrons

Question 5

Which process explains the flame colour produced by the compounds of Group 1 elements?
A- absorption of visible light energy as electrons are promoted to higher energy levels.
B- absorption of visible light energy as electrons are removed from gaseous atoms.
C- emission of visible light energy as electrons return to lower energy levels.
D- emissions of visible light energy as electrons are added to gaseous ions.

Answer 5

C- emission of visible light energy as electrons return to lower energy levels.

Question 6

When sodium chlorate(I), NaClO, is heated, sodium chlorate (V) and sodium chloride are formed.
(i) Write the ionic equation for this reaction
(ii) What type of reaction is this?

Answer 6

(i) 3OCl- —-> ClO3- + 2Cl-
(ii) Disproportionation.

Question 7

Name a reagent that could be used to confirm that a solution contains iodine, and state what would be seen. (2)

Answer 7

starch
blue-black.

Question 8

How could you confirm that a solution said to be HCl(aq) contained chloride ions?

Answer 8

• add silver nitrate
• white ppt
• soluble in dilute ammonia.

Question 9

Hydrogen chloride is soluble in water. Explain why the solution is acidic.

Answer 9

changes into ions as it dissolves.

Question 10

Give a chemical test for chlorine, stating what you would do and what you would see. (2)

Answer 10

damp litmus paper
bleached.

Question 11

Iodine, I2, can be reduced to iodine ions, I- by tin(II) ions, Sn2+, which are themselves oxidised to tin(IV) ions, Sn4+
(i) Construct the oxidation and reduction half-equations for the above system.

Answer 11

Sn2+ - 2e- —> Sn4+
I2+2e- —->2I-

Question 11

(ii) Use the above half equations to construct the overall ionic equation for the reaction. (1)

Answer 11

Sn2+I2 —>Sn4+ + 2I-

Question 12

Define reduction in terms of change in oxidation number. (1)

Answer 12

decrease in oxidation number of an element.

Question 13

Write an ionic half-equation for the reduction of chlorine molecules to chloride ions. State symbols are not required. (1)

Answer 13

Cl2 + 2e(−) → 2Cl-

Question 14

Write an ionic half-equation for the oxidation of chlorine molecules to chlorate(I) ions in the presence of cold, aqueous hydroxide ions. State symbols are not required. (1)

Answer 14

Cl2 + 4OH- → 2ClO- + 2H2O + 2e(−)

Question 15

Combine the two equations in (a)(i) and (ii) to give the ionic equation for the reaction of chlorine molecules with cold, aqueous hydroxide ions. (1)

Answer 15

Cl2 + 2OH- → Cl- + ClO- + H2O

Question 16

Use your answer to (a)(iii) to explain why the reaction is described as a disproportionation reaction.

Answer 16

• disproportionation is simultaneous oxidation and reduction of an element in the same species (1)
• chlorine changes from 0 to -1 and +1 (1)

Question 17

Which element in group 7 has the highest first ionisation energy. (1)

Answer 17

A - iodine
B- bromine
C- chlorine
D- fluorine.

Question 18

The first five ionization energies of an element, X, are: 578, 1817, 2745, 11578 and 14831 kJ mol-1, respectively. In which group of the Periodic Table is X found?
A- 1
B- 2
C- 3
D- 4

Question 19

21 (a) (i) An alkaline solution is produced when barium reacts with cold water. Write the equation for this reaction, including all state symbols. (2)

Answer 19

Ba(s) +2H2O(l)-> Ba(OH)2(aq) + H2(g)

Question 20

(ii) The reaction in (a)(i) is a redox reaction. State the initial and final oxidation number of any element that changes its oxidation number. (2)

Answer 20

• Ba(increases in ON) from 0 to +2 (1)
• H (decreases in ON) from +1 to 0(1)

Question 21

b) Dilute hydrochloric acid is added to the solution produced in (a)(i). Write the equation for the reaction which occurs. State symbols are not required. (1

Answer 21

Ba(OH)2 + 2HCl->BaCl2 +2H2O

Question 22

An oxidising agent
A- gains electrons and is oxidised
B- loses electrons and is oxidised
C- gains electrons and is reduced
D- loses electrons and is reduced

Answer 22

C- gains electrons and is reduced