Revision questions

Use your laboratory notebook to attempt this question.

QUESTION

Describe what is observed (with the aid of equations) in each of the following reactions.

(a) Aqueous NaOH is added to aq iron(III) sulphate.

(b) Dilute HCl is added to solid sodium carbonate.

(c) Aqueous barium chloride is added to dilute sulphuric acid.

(d) Aqueous silver nitrate is added to aq sodium chloride. (8 mks)

ANSWERS

(a) A rusty-brown precipitate is formed, which is insoluble in excess NaOH.

Fe3+(aq) + 3OH-(aq) Fe(OH)3 (s)

(b) Sodium carbonate would dissolve and a gas would be given off.

Na2CO3(s) + 2HCl (aq) 2NaCl (aq) +

H2O(l) + CO2 (g)

(c) A white precipitate will be seen, which will remain insoluble.

Ba2+(aq) + SO42-(aq) BaSO4(s)

(d) The silver nitrate would react with the chloride ions to form a white precipitate of silver chloride. Ag+(aq) + Cl-(aq) AgCl (s)

QUESTION

The effect of heat on compounds of metals may be predicted from the position of the metals in the reactivity series.

(a) How would the action of heat on potassium carbonate differ from the action of heat on copper (II) carbonate? Give the relevant equation(s).

(b) When most nitrates are heated, one or two gases may be given off. From the nitrates of the metals sodium, calcium, magnesium and zinc, select one nitrate that (i) gives off one gas (ii) gives off two gases. Give the equation of the reaction in (ii) above.

(c) In the reactivity series, metal X is placed below zinc but above copper.

(i) What happens when the hydroxide of copper is heated?

(ii) What products would you expect to obtain when the hydroxide of X is heated in a dry test tube?

(iii) Metal X forms the X2+ ion. Write a balanced equation, using X as the symbol for the metal, for the reaction that you would expect to take place when the hydroxide of X is heated in a dry test tube.

ANSWERS

(a) Potasium carbonate is stable and not decomposed by heat, while copper (II) carbonate would be decomposed by heat.

K2CO3 (s) K2CO3 (s) (stable to heat) CuCO3 CuO (s) + CO2 (g) (decomposed by heat)

(b) (i) Sodium nitrate gives off only one gas (oxygen) when heated.

(ii) Calcium, magnesium and zinc nitrates produce two gases (oxygen and nitrogen dioxide) when heated.

2Mg (NO3)2 (s) 2MgO (s) +

4NO2 (g) + O2 (g)

(c) When copper hydroxide is heated, it decomposes to form copper oxide and steam.

(ii) If the hydroxide of X is heated in a dry test tube, one would expect to obtain the oxide of X and steam.

(iii) If the ion of X is X2+, then the formula of its hydroxide is

X(OH)2.

Therefore, X(OH)2 (s) XO (s) + H O (g) 2