1.8 The Periodic Table

Section A

For each of the following questions only one of the lettered responses (A-D) is correct.

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the response sheet.

1.B Which one of the following equations does not represent a reaction of chlorine under suitable conditions?

A Cl₂ + H₂O HCl + HOCl

B 2Cl₂ + CH₄ CCl₄ + 2H₂

C 3Cl₂ + 6NaOH 5NaCl + NaClO₃ + 3H₂O

D Cl₂ + 2NaOH NaCl + NaOCl + H₂O

2.A When the hydrogen halides dissolve in water acidic solutions are formed. Which has the highest pH (assuming all are equal concentrations)?

A Hydrogen fluoride

B Hydrogen chloride

C Hydrogen iodide

D Hydrogen bromide

3. In which one of the following changes has chlorine been oxidised?

A 3Cl₂ + 2Fe 2FeCl₃

B Cl₂ + I₂ 2IC1

C Cl₂ + 2KBr Br₂ + 2KCl

D Cl₂ + 2KOH H₂O + KClO + KCl

4. In which one of the following sequences are the oxides of the elements classified as basic, amphoteric and acidic respectively?

A Na, Mg, Al

B Na, K, S

C K, Al, P

D S, P, Mg

5. Which one of the following is true of the halogens as the Group is descended from chlorine to iodine?

A The atomic radius decreases.

B The colour of the element lightens.

C The melting point of the element increases.

D The oxidising power of the element increases.

5. Which one of the following equations represents a reaction of chlorine?

A Cl₂ + NaOH NaOCl + HCl

B Cl₂ + Fe FeCl₂

C Cl₂ + H₂O HCl + HOCl

D Cl₂ + CH₄ CH₂Cl₂ + H₂

SECTION B

1. The group in the Periodic Table headed by fluorine is called the halogen group.

(a) Using your knowledge of the group predict the colour and physical state of astatine.

Black (1)/ solid (1) [2]

(b) When chlorine gas is bubbled through a solution of potassium iodide a redox reaction occurs.

(i) What is observed in this reaction?

The colour of the gas disappears (1)/ Solution turns colourless to dark brown (1)

[2]

(ii) What is meant by a redox reaction?

A reaction in which one or more electrons (1)/ is~are transferred from one substance to another (1)

[2]

(iii) Explain fully the changes undergone (if any) by the potassium and iodide ions.

Potassium ion : no change (1)/ iodide ion : loses electron to form iodine (1) [2]

(c)

(i) The presence of iodide ions in an aqueous solution of sodium iodide can be detected using silver nitrate solution and ammonia solution. Describe fully how you would carry out this procedure experimentally, stating any changes you observe. Write equations for any reactions which occur.

Add dilute nitric acid followed by silver nitrate solution (1) to the iodide solution/ A pale yellow (1)/ precipitate (1)/ of silver iodide (1)/ forms. This is insoluble in ammonia solution. (1)/ AgNO₃ + NaI = AgI + NaNO₃ (1)

[6]

(ii) State what differences you would observe if the sodium iodide solution was replaced by sodium chloride solution. Write equations for any reactions which occur.

With sodium chloride a white (1) precipitate of silver chloride forms. This is soluble in ammonia solution (1)

[4]

2. Sodium bromide reacts with concentrated sulphuric acid at room temperature to give four products. Place ticks (√) in four of the boxes to show which substances are formed.

√ if the substance is formed

bromine

hydrogen

hydrogen bromide

hydrogen sulphide

sodium hydrogensulphate

sulphur

sulphur dioxide

[3]

3. The diagram below shows chlorine gas being passed through a dilute

solution of potassium iodide. The upper layer is a hydrocarbon solvent.

(a) (i) What is the most important safety precaution to take when carrying

out the experiment?

The colour of the gas disappears (1)/ Solution turns colourless to dark brown (1)

[1]

(ii) Write the ionic equation for the reaction between chlorine and potassium iodide and explain the redox reactions taking place in terms of electron transfer.

With sodium chloride a white (1) precipitate of silver chloride forms. This is soluble in ammonia solution (1)

[3]

(b) When the aqueous layer is shaken with the hydrocarbon most of the iodine dissolves in the upper layer.

(i) What is the colour of iodine in potassium iodide solution?

[1]

(ii) What does the greater solubility in the hydrocarbon suggest about the bonding in iodine?

The colour of the gas disappears (1)/ Solution turns colourless to dark brown (1)

[1]

(iii) The percentage composition of the elements in the solvent is:

element	% composition by mass
carbon	92.3
hydrogen	7.7

Calculate the empirical formula of the solvent.

[2]

(c) If the hydrocarbon layer is shaken with aqueous sodium thiosulphate the colour disappears.

(i) Write an equation for the reaction between iodine and sodium thiosulphate.

[2]

(ii) If insufficient thiosulphate solution were added traces of iodine are left which are not visible to the eye. Name a reagent that could be added to detect the iodine and state the colour produced.

[2]