(a)i. With the aid of an equation, explain briefly why aluminum metal is not affected by air.
(ii) In the extraction of aluminum from bauxite, state the:
– substance used for purifying the ore;
– composition of the mixture electrolyzed.
(b) ZnO is an amphoteric oxide. Write equations to illustrate this statement.
(c)i) List three uses of sodium trioxocarbonate(IV).
(ii) Explain briefly why a solution of trioxonitrate(V) acid turns yellowish on storage for some time.
(ii) Describe briefly how trioxonitrate(V) ions could be tested for in the laboratory.
(d) Write balanced chemical equations for the preparation of hydrogen chloride.
(i) using concentrated H\(_{2}\)SO\(_{4}\):
(ii) by direct combination of its constituent elements.
(iii) State one use of hydrogen chloride.
Explanation
(a) Aluminum first reacts With oxygen in the air to form a film of oxide/oxide layer on the Surface.
Al\(_{(s)}\) + 3O2\(_{(g)}\) \(\implies\) 2AlO3\({(s)}\). The film of oxide formed is not porous and insoluble in water (in the air) and hence protects the metal underneath from further attack. OR The film of oxide coats the metal and prevents it from further attack.
(ii) The composition of the ore:- Cryolite / Na\(_{3}\)AlF\(_{6}\) -Aluminà / Al\(_{2}\)O\(_{3}\)
(b) ZnO is an amphoteric oxide. Write an equation to illustrate this statement.
ZnO\(_{(s)}\) + 2HCl\(_{(aq)}\) \(\implies\) ZnCl\(_{2(aq)}\) + H\(_{2}\)O\(_{(l)}\); ZnO\(_{(s)}\) + 2NaOH\(_{(aq)}\) + Na\(_{2}\)ZnO\(_{2(aq)}\) + H\(_{2}\)O\(_{l}\)
(c)i. List three uses of Sodium Trioxocarbonate(IV):
- Glass production.
- Water treatment/ softening hard water
- Preparation of baking powder.
- Removal of sulfur (IV) Oxide in power stations.
- As a standard alkali in acid-base titration.
- As an analytical reagent.
- Production of rayon polymer.
- As a household cleaning agent used in laundry.
- As food additive.
- Used in textile industry.
- In petroleum refining.
- Manufacturing of other sodium compounds.
- production of soaps and detergents
- paper production
- production/ preparation of NaHCO\(_{3}\)
(ii) Explain briefly why a solution of trioxonitrate( V) acid turns yellowish on storage for sometime:- The yellowish color is caused by dissolved nitrogen(IV) oxide which results from the slow decomposition of the acid.
(iii) Describe briefly how trioxonitrate (V) ions could be tested for in the laboratory:-
To the solution, add freshly prepared iron (ll) tetraoXoSulphate (Vl) solution and followed by Conc H\(_{2}\)SO\(_{4}\), a brown ring is observed or warm the solid with ( copper turnings and ) Conc. H\(_{2}\)SO\(_{4}\) in a test tube. Brown fumes are observed.
(d)i. H\(_{2}\)SO\(_{4(aq)}\) + 2NaCl\({s}\) \(\implies\) Na\(_{2}\)SO\(_{4(aq)}\) + 2HCl\(_{g}\). OR
H\(_{2}\)SO\(_{4}\) + 2KCl \(\implies\) K\(_{2}\)SO\(_{4(aq)}\) + 2HCI (ll) H\(_{2(g)}\) + Cl\(_{2(g)}\) \(\implies\) 2HCl\(_{(g)}\)
(ii) State one use of hydrogen chloride:
- Manufacturing of drug.
- Cleaning
- Pickling
- Electroplating metals
- Tanning leather
- Refining
-Production of CH\(_{3}\)Cl/PVC/plastics.