(a)(i) List two elements which react with steam at red heat to produce hydrogen.
(ii) Explain why an aqueous solution of potassium bromide turned reddish brown on bubbling chlorine through it.
(iii) Write an equation for the reaction in (a)(ii).
(b)(i) Name two types of chemical industry that use limestone as raw material.
(ii) Give one example of hygroscopic substances.
(iii) Copy and complete the table below.
| Salt to be prepared |
Starting material |
Method of preparation |
| \(\mathrm{PbSO_4}\) |
\(\mathrm{Pb(NO_3)_{2(ag)}}\) |
- |
| \(\mathrm{KNO_3}\) |
\(\mathrm{KOH}\) |
Neutralization |
| \(\mathrm{CaCl_2}\) |
\(\mathrm{CaCO_3}\) |
- |
| \(\mathrm{FeCl_3}\) |
\(\mathrm{Fe_{(s)}}\) |
- |
| \(\mathrm{CuSO_4}\) |
\(\mathrm{CuO}\) |
- |
(c) In the contact process for the manufacture of tetraoxosulphate (VI) acid;
(i) State how sulphur (IV) oxide is obtained;
(ii) Write an equation for the reaction that takes place in the catalyst chamber;
(iii) Give the steps required to convert sulphur (VI) oxide to acid.
(d)(i) List two disadvantages of hard water.
(ii) Mention three methods which can be used to remove both permanent and temporary hardness in water at the same time.
(iii) State the role of alum and chlorine respectively in the purification of water for town supply.
(a)(i) Two elements that react with steam at red heat to give hydrogen: iron (Fe) and zinc (Zn). (Magnesium is also acceptable.)
(a)(ii) Why aqueous potassium bromide turns reddish-brown with chlorine
Chlorine is a stronger oxidising agent (higher in the halogen reactivity/electrochemical series) than bromine, so it displaces bromine from the bromide solution. The reddish-brown colour is the free bromine liberated.
(a)(iii) Equation
\[ \text{Cl}_2 + 2\text{KBr} \rightarrow 2\text{KCl} + \text{Br}_2 \]
(b)(i) Two industries that use limestone as raw material: the cement industry and the glass industry (iron and steel manufacture is also acceptable).
(b)(ii) One example of a hygroscopic substance: concentrated tetraoxosulphate(VI) acid (concentrated H\(_2\)SO\(_4\)). (Quicklime, CaO, is also acceptable.)
(b)(iii) Completed table
| Salt to be prepared | Starting material | Method of preparation |
|---|
| PbSO\(_4\) | Pb(NO\(_3\))\(_2\)(aq) | Precipitation (double decomposition, adding dilute H\(_2\)SO\(_4\)) |
| KNO\(_3\) | KOH | Neutralisation |
| CaCl\(_2\) | CaCO\(_3\) | Action of dilute hydrochloric acid on the trioxocarbonate(IV) |
| FeCl\(_3\) | Fe(s) | Direct combination (heating iron in dry chlorine) |
| CuSO\(_4\) | CuO | Neutralisation (action of dilute H\(_2\)SO\(_4\) on the base) |
(c) Contact process
- (i) Sulphur(IV) oxide is obtained by burning sulphur in air/oxygen, S + O\(_2\) \(\rightarrow\) SO\(_2\), or by roasting a sulphide ore such as iron pyrites.
- (ii) In the catalyst chamber (vanadium(V) oxide catalyst, about 450 \(^{o}\)C): \[ 2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3 \]
- (iii) The sulphur(VI) oxide is absorbed in concentrated tetraoxosulphate(VI) acid to form oleum, SO\(_3\) + H\(_2\)SO\(_4\) \(\rightarrow\) H\(_2\)S\(_2\)O\(_7\); the oleum is then diluted with the correct amount of water, H\(_2\)S\(_2\)O\(_7\) + H\(_2\)O \(\rightarrow\) 2H\(_2\)SO\(_4\). (SO\(_3\) is not passed directly into water because the reaction is too violent and forms an acid mist.)
(d)(i) Two disadvantages of hard water:
- It wastes soap, forming an insoluble scum before a lather is produced.
- It deposits scale (fur) in kettles, boilers and pipes, which wastes fuel and can block the pipes.
(d)(ii) Three methods that remove both permanent and temporary hardness at once: addition of washing soda (sodium trioxocarbonate(IV)), distillation, and the ion-exchange (permutit) method.
(d)(iii) Roles in town water purification:
- Alum: a coagulant - it makes fine suspended and colloidal particles clump together and settle out.
- Chlorine: a disinfectant/steriliser - it kills bacteria and other harmful micro-organisms.
(a)(i) Two elements that react with steam at red heat to give hydrogen: iron (Fe) and zinc (Zn). (Magnesium is also acceptable.)
(a)(ii) Why aqueous potassium bromide turns reddish-brown with chlorine
Chlorine is a stronger oxidising agent (higher in the halogen reactivity/electrochemical series) than bromine, so it displaces bromine from the bromide solution. The reddish-brown colour is the free bromine liberated.
(a)(iii) Equation
\[ \text{Cl}_2 + 2\text{KBr} \rightarrow 2\text{KCl} + \text{Br}_2 \]
(b)(i) Two industries that use limestone as raw material: the cement industry and the glass industry (iron and steel manufacture is also acceptable).
(b)(ii) One example of a hygroscopic substance: concentrated tetraoxosulphate(VI) acid (concentrated H\(_2\)SO\(_4\)). (Quicklime, CaO, is also acceptable.)
(b)(iii) Completed table
| Salt to be prepared | Starting material | Method of preparation |
|---|
| PbSO\(_4\) | Pb(NO\(_3\))\(_2\)(aq) | Precipitation (double decomposition, adding dilute H\(_2\)SO\(_4\)) |
| KNO\(_3\) | KOH | Neutralisation |
| CaCl\(_2\) | CaCO\(_3\) | Action of dilute hydrochloric acid on the trioxocarbonate(IV) |
| FeCl\(_3\) | Fe(s) | Direct combination (heating iron in dry chlorine) |
| CuSO\(_4\) | CuO | Neutralisation (action of dilute H\(_2\)SO\(_4\) on the base) |
(c) Contact process
- (i) Sulphur(IV) oxide is obtained by burning sulphur in air/oxygen, S + O\(_2\) \(\rightarrow\) SO\(_2\), or by roasting a sulphide ore such as iron pyrites.
- (ii) In the catalyst chamber (vanadium(V) oxide catalyst, about 450 \(^{o}\)C): \[ 2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3 \]
- (iii) The sulphur(VI) oxide is absorbed in concentrated tetraoxosulphate(VI) acid to form oleum, SO\(_3\) + H\(_2\)SO\(_4\) \(\rightarrow\) H\(_2\)S\(_2\)O\(_7\); the oleum is then diluted with the correct amount of water, H\(_2\)S\(_2\)O\(_7\) + H\(_2\)O \(\rightarrow\) 2H\(_2\)SO\(_4\). (SO\(_3\) is not passed directly into water because the reaction is too violent and forms an acid mist.)
(d)(i) Two disadvantages of hard water:
- It wastes soap, forming an insoluble scum before a lather is produced.
- It deposits scale (fur) in kettles, boilers and pipes, which wastes fuel and can block the pipes.
(d)(ii) Three methods that remove both permanent and temporary hardness at once: addition of washing soda (sodium trioxocarbonate(IV)), distillation, and the ion-exchange (permutit) method.
(d)(iii) Roles in town water purification:
- Alum: a coagulant - it makes fine suspended and colloidal particles clump together and settle out.
- Chlorine: a disinfectant/steriliser - it kills bacteria and other harmful micro-organisms.
