Engineering Chemistry Multiple Choice Questions on “Analysis of Coal”.
1. In analysis of coal, determination of _______ is done by Kjeldahl method.
a) Volatile matter
b) Nitrogen
c) Ash
d) Oxygen
Answer: b
Clarification: In ultimate analysis of coal, Nitrogen is determined by Kjeldahl method. The method involves 3 steps which are digestion, distillation and titration. In digestion, sample is digested in boiling concentrated sulphuric acid in presence of catalyst and ammonium sulphate is obtained. In distillation, excess NaOH solution is added and ammonia is obtained. In titration, ammonia is determined by volumetric acid solution. The result can be expressed in terms of %N.
2. In determination of carbon and hydrogen by ultimate analysis, increase in weight of calcium chloride bulb represents ______
a) weight of water formed
b) weight of carbon dioxide formed
c) carbon
d) hydrogen
Answer: a
Clarification: The gaseous products of combustion are passed through two bulbs. One containing weighed amount of anhydrous Calcium chloride which absorbs water other containing weighed amount of potassium hydroxide which absorbs carbon dioxide.
3. Hydrogen available for combustion is lesser than the actual one.
a) true
b) false
Answer: a
Clarification: Oxygen is present in combined form with hydrgen in the coal. It is very difficult to break hydrogen-oxygen bond and hence, that combined form of hydrogen is not available for combustion. Thus, free hydrogen available for combustion is lesser than the actual one.
4. Good quality of coal should have _____ % of oxygen.
a) low
b) high
c) 100
d) 0
Answer: a
Clarification: Good quality of coal should have less % of oxygen because increase in 1% oxygen content decreases calorific value approximately by 1.7%. Ideal fuel should have high calorific value and hence, less %oxygen.
5. Percentage of ash by analysis of coal is given by _____
a) (weight of residue/weight of sample) × 100
b) (weight of sample – weight of residue) × 100
c) (weight of sample – weight of residue)/weight of sample × 100
d) (weight of residue – weight of sample) × 100
Answer: a
Clarification: Ash is weight of residue obtained after complete combustion of 1 g of coal at 700‐750°C. Ash in % is given by, %A = (weight of residue/weight of sample) × 100.
6. In coal, Sulphur is usually present in the extent of __________
a) 0.5-3%
b) 90-95%
c) 70-75%
d) 80-85%
Answer: a
Clarification: Sulphur is generally present in the extent of 0.5 to 3% and is usually derived from ores like gypsum, iron pyrites, etc. High percentage of sulphur in coal is undesirable to be used for making coke in the iron industry since it affects the quality and properties of steel.
7. In ultimate analysis, %hydrogen is given by __________
a) (Increase in weight of CaCl2 tube×2×100 / weight of coal sample taken×18)
b) (Increase in weight of KOH tube×2×100 / weight of coal sample taken×18)
c) (Increase in weight of CaCl2 tube×4×100 / weight of coal sample taken×18)
d) (Increase in weight of KOH tube×4×100 / weight of coal sample taken×18)
Answer: a
Clarification: %hydrogen= (weight of hydrogen/weight of coal sample taken) × 100
In ultimate analysis of coal,
%H = (Increase in weight of CaCl2 tube×2×100 / weight of coal sample taken×18).
8. In ultimate analysis, %carbon is given by __________
a) (Increase in weight of KOH tube×12×100 / weight of coal sample taken×44)
b) (Increase in weight of KOH tube×2×100 / weight of coal sample taken×18)
c) (Increase in weight of CaCl2 tube×12×100 / weight of coal sample taken×44)
d) (Increase in weight of CaCl2 tube×2×100 / weight of coal sample taken×18)
Answer: a
Clarification: %C = (weight of carbon/weight of coal sample taken) ×100
In the ultimate analysis of coal,
%C = (Increase in weight of KOH tube×12×100 / weight of coal sample taken×44).
9. __________ is the weight of residue obtained after burning a weighed amount of dry coal.
a) Ash
b) Volatile matter
c) Moisture
d) Carbon
Answer: a
Clarification: Ash is an unwanted matter and non-combustible which is the residue left after all combustible substances are burnt off. %Ash= (weight of ash formed/weight of dry coal taken) × 100.
10. In proximate analysis of coal, %fixed carbon = __________
a) 100 – % (ash + volatile matter + moisture)
b) 100 – % (ash + moisture)
c) 100 – % (ash + moisture) + %volatile matter
d) 100 – % (moisture + volatile matter)
Answer: a
Clarification: In proximate analysis of coal, firstly percentage of ash, volatile matter and moisture is found out. Percentage of fixed carbon can be found out by subtracting the above percentages from 100 since coal consists of ash, moisture, volatile matter and fixed carbon.