Exam-style Questions: Group VII

1. Astatine (As) is a member of Group VII of the periodic table.

(You may consult a data book if necessary for this question)

a) What is the colour and state of Astatine at room temperature?

(2 marks)

b) What is the oxidation number of As in NaAsO3?

(1 mark)

c) Write an equation to show the reaction between astatine and cold
aqueous sodium hydroxide.

(1 mark)

d) Predict the bond energy of H-As bond.

(1 mark)

e) Chlorine gas is passed through an aqueous solution of potassium astatide,
KAt. Write an equation to show what reaction will take place.

(1 mark)

f) Under certain conditions it is possible for the following reaction
to take place:

3AsO- = 2As- + AsO3-

What is the name given to this type of reaction?

(1 mark)

g) Give a method for testing for the presence of astatide
ions in aqueous solution.

(2 marks)

(Marks available: 9 marks)

Answer

Answer outline and marking scheme for question: 1

a) Astatine will be a black(1) solid(1)

(2 marks)

b) Oxidation number = +5

(1 mark)

c) Predict the bond energy of H-As bond.

(1 mark)

d) Bond energies / kJmol-1

H-F = 562

H-Cl = 431

H-Br = 366

H-I = 299

H-As = ?

From pattern between H-Cl and H-I.: Bond energy of H-As = 232 kJmol-1 (1)

(1 mark)

e) Cl2(g) + 2As-(aq) = As2(s)
+ 2Cl-(aq)

(1 mark)

f) Disproportionation

(1 mark)

g) Add aqueous silver nitrate (1)

Presence of astatide ions would be indicated by a dark yellow / orange precipitate
of AgAs (1)

(2 marks)

(Marks available: 9)