Question 4
- (i) What is hardwater?
(ii) State one salt that causes:
I. temporary hardness:
II. permanent hardness.
(iii) Give two methods by which permanent hardness could be removed. [6 marks] - (i) List four basic processes that are used for purification of water for town supply.
(ii) List three chemicals that are used for the purification of water for two supply. [7 marks] - (i) Define the term solubility.
(ii) If 1.11g of calcium chloride (CaCl2) were dissolved in 20.0g of distilled water at 20oC, calculate the solubility of the salt in moldm-3. [Ca 40.0, Cl 35.5] [6 marks] - Give the reagent(s) that could be used to distinguish between each of the following pairs of compounds.
I. CH3(CH2)2CH2OH and CH3CH2OH
II. CH3CH2C =CH and CH3C = CCH3
III. CH3CH2CH2CH3 and CH3CH2C = CH2 [3 marks] - Consider the compound below.
CH3CONH2CH2OH
(i) Draw the structure of the compound.
(ii) Name the functional group(s) present in the compound. [3 marks]
Observation
The question was popular among the candidates
In part (a), majority of the candidates correctly defined hard water, and listed the salts that caused temporary and permanent hardness.
In part (b), majority of the candidates listed the four basic processes used for purification of water for town supply.
In part (c), some candidates could not define solubility correctly and calculate the solubility in the given question. Their performance in the question was fair.
In part (d), majority of the candidates could not give the reagent(s) that could be used to distinguish between each of the given compounds.
The expected answer include
- (i) Hard water is water that does not lather readily with soap / wastes soap.
(ii) I. - Ca(HCO3)2
- Mg(HCO3)2
II. - CaSO4
- MgSO4
- CaCl2
- MgCl2
- FeCl3
(iii) - By adding washing soda / Na2CO3
OR
MgSO4 + Na2CO3 →Na2SO4+ MgCO3
- Adding caustic soda / NaOH OR
CaSO4 + 2NaOH →Ca(OH)2 + Na2SO4
- By using ion – exchange resin / permutite / zeolite OR
CaSO4 + Na zeolite → Ca zeolite + Na2SO4
- Distillation - (i) - aeration
- coagulation / floculation
- sedimentation
- filtration
- disinfection
(ii) - Potash alum KAl(SO4)2 / NaAlO2
- Chlorine
- Iodine / Iodide
- fluorine / flouride
- Ca (OH)2 / CaO
- CuSO4 - (i) Solubility of a solute in a solvent at a particular temperature is the maximum amount of the solute in moles or grams that will saturate 1 dm3 of the solvent at that temperature.
OR
The amount of solute that will dissolve in I dm3 of solvent at a particular temperature in the presence of undissolved solute
(ii)
-
I. KMnO4 / I2 / NaOH
II. NH3 / AgNO3 // NH3/ CuCl
III. Br2 / CCl4 // H+/ KMnO4 // H+ / K2 Cr2 O7, Bromine water - (i)
(ii) - Amide
- hydroxyl / hydroxy