(a) (i) What is meant by hardness of water?
(ii) Describe briefly how you would determine what proportion of hardness in a given sample of water is due to permanent hardness.
(iii) Give two reasons why hardness of water is an undesirable property.
(b) State the:
(i) reagents;
(ii) conditions for the laboratory preparation of trioxonitrate (V) acid.
(iii) How does concentrated trioxonitrate (V) acid reacts with:
(I) sulphur;
(II) aluminium.
(c) Name one amphoteric oxide.
Explanation
(a) (i) When water does not easily form lather with soap / when water contains dissolved calcium and magnesium salts.
Water that does not easily lather with soap / Water that contains dissolved calcium and magnesium salts
(ii) Prepare soap solution
Measure volume of sample water from a burette or pipette titratewith shaking to permanent lather.
take titre value say x cm(^3)
Measure same volume of boiled sample water and then titrate with shaking take titre value say y cm(^3)
Find ratio; (frac{text{permanent}}{text{Total}}) = (frac{y}{x})
(iii) Waste of soap
– produces scum during washing with soap
– blockage of pipes
– scales in boilers / furring of kettles
– leads to wastage of fuel
– not suitable for tanning / laundry / textile/ paper manufacturing industries
(b) (i) NaNO(_3) or KNO(_3)
conc H(_2)SO(_4)
(ii) concentrated H(_2)SO(_4)
heat (over a sand bath)
all glass apparatus
(iii) 2HNO(_3) + S → H(_2)SO(_4) + 2NO OR
6HNO(_3) + S → H(_2)SO(_4) + 6NO(_2) + 2H(_2)O
II. no reaction / reaction prevented / metal passive oxide formed which coats metal
(c) Zinc oxide
Lead (II) oxide
Aluminium oxide
Tin(IV)oxide
Aluminium hydroxide
Tin (II) oxide
Lead (IV) oxide
Beryllium oxide