250+ TOP MCQs on Organic Chemistry – Quantitative Analysis and Answers

Chemistry Problems for NEET Exam on “Organic Chemistry – Quantitative Analysis”.

1. Carbon and hydrogen are detected by heating the compound with ____________ during quantitative analysis.
a) carbon dioxide
b) copper (II) oxide
c) magnesium oxide
d) sulphur dioxide
Answer: b
Clarification: During quantitative analysis, a known quantity of the organic compound is burned in the presence of excess of oxygen and copper (II) oxide. The carbon present in the compound is oxidized to carbon dioxide and the hydrogen is transformed to water.

2. On complete combustion, 0.500 g of an organic compound gave 0.150 of carbon dioxide. Determine the percentage composition of carbon in the compound.
a) 8.18%
b) 81.8%
c) 0.81%
d) 81%
Answer: a
Clarification: The required equation is:
Percentage of carbon = 12 * m2 * 100/ 44 * m
In this case, m = 0.500
m2 = 0.150
Substituting in the equation → Percentage of carbon = 12 * 0.150 * 100/ 44 * 0.500
= 8.18%
Therefore, the percentage of carbon present in the organic compound is 8.18%.

3. The amounts of water can be detected by the increase in the mass of __________ during quantitative analysis of hydrogen.
a) potassium hydroxide
b) sodium hydroxide
c) sodium chloride
d) calcium chloride
Answer: d
Clarification: In the quantitative analysis of hydrogen, hydrogen is converted to water. Then, water is passed through a u-tube containing calcium chloride. Calcium chloride absorbs water and thereby, increases in mass. This increase in the mass of calcium chloride gives the amounts of water present in the organic compound.

4. Dumas method is a method of estimation of nitrogen.
a) True
b) False
Answer: a
Clarification: One of the methods of quantitative analysis of nitrogen includes Dumas method. In Dumas method, the nitrogen containing organic compound is heated with copper oxide in an atmosphere of carbon dioxide and this leads to the formation of free nitrogen in addition to carbon dioxide and water.

5. 0.350 g of an organic compound gave 100 ml of nitrogen collected at 250 K temperature and 700 mm pressure. Calculate the percentage composition of nitrogen in the compound. Use Dumas method.
a) 25.70%
b) 35%
c) 35.71%
d) 36.88%
Answer: c
Clarification: Here, p = 700 mm; v = 100 ml; t =250 K
Volume of nitrogen at STP = p * v * 273/ 760 * t
= 700 * 100 * 273/ 760 * 250
= 100.57 ml
22,400 ml of nitrogen at STP weighs = 28 g
Then, 100.57 ml of nitrogen weighs = 28 * 100.57/22400
= 0.125 g
Therefore, percentage of nitrogen = 0.125 * 100/0.350
= 35.71%
So, percentage of nitrogen in the organic compound is 35.71%.

6. In Kjedahl’s method of estimation of nitrogen, the compound containing nitrogen is heated with __________
a) concentrated hydrochloric acid
b) concentrated sulphuric acid
c) nitric acid
d) dilute hydrochloric acid
Answer: b
Clarification: The compound containing nitrogen is heated with concentrated sulphuric acid. This leads to the conversion of nitrogen to ammonium sulphate. The resulting acid is then heated with excess of sodium hydroxide. The liberated ammonia gas is absorbed in excess of standard solution of sulphuric acid. The amount of ammonia produced is determined by estimating the amount of sulphuric acid consumed in the reaction.

7. Using Carius method, find out the percentage of bromine in the compound if 0.450 g of organic compound gave 0.200 g of AgBr. (Given: molar mass of Ag = 108; molar mass of Br = 80)
a) 18%
b) 17%
c) 17.68%
d) 18.91%
Answer: d
Clarification: The molar mass of AgBr = 108 + 80
= 188 g
So, 188 g of AgBr contains 80 g of Br.
Then, 0.200 g of AgBr contains 80 * 0.200/ 188 = 0.085 g bromine
Therefore, percentage of bromine = 0.085 * 100/ 0.450
= 18.91%
Thus, the percentage of bromine (halogen) using Carius method is 18.91%.

8. In the estimation of sulphur, the organic compound is heated with ___________ in a carius tube.
a) sodium hydroxide
b) sodium peroxide
c) potassium hydroxide
d) calcium chloride
Answer: b
Clarification: In the estimation of sulphur, a known quantity of the organic compound is heated with sodium peroxide. This facilitates the sulphur present to be oxidized to sulphuric acid. It is precipitated as barium sulphate by adding excess of barium chloride solution in water. The percentage of sulphur can be estimated from the mass of barium sulphate.

9. Estimation of oxygen can be determined by Carius method.
a) True
b) False
Answer: b
Clarification: Carius method is used for the estimation of halogens present in an organic compound. Percentage of oxygen present in organic compound can be calculated by the difference between the total percentage composition (100) and the sum of the percentages of all other elements. The percentage of oxygen can also be derived from the amount of iodine produced.

10. The elements present in a compound are determined by apparatus called ____________
a) analyzer
b) CHN elemental analyzer
c) chemical analyzer
d) elemental analyzer
Answer: b
Clarification: The elements like carbon, hydrogen, and nitrogen present in an organic compound are determined by an apparatus called as CHN elemental analyzer. The analyzer requires only a very small amount of the substance (1-3 mg) and displays the values on a screen within a short time.

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