CBSE Class 11 Chemistry VBQs Basic Concepts Of Chemistry

Question. Two friends Riya and Pooja were discussing that which is better for expressing the concentration of a solution: Molality or Molarity ?Pooja told Riya that Molality is considered better for expressing the concentration as compared to Molarity and explained the reason as well.

(i) What would be the explanation of Pooja?

(ii) What are the units of molarity & molality?

(iii) What is the difference between molality & molarity?

Question. Mohan learnt the term mol in his chemistry class. He discussed the term mol with her elder sister Anshika. Anshika explained about and then Mohan got satisfied.

(i) What was the probable answer given by Anshika ?

(ii) What for term mol stands?

(iii) What values are associated with Anshika?

Question. Radhika ,Supriya and Hema were asked by the PGT chemistry to find the mass of a metal piece independently one by one using the same balance and same weight box. Each student was asked to take three observations. The students reported their result as shown in the following table: 

If the actual mass of the metal piece is 1.325g and the permitted uncertainty in the measurement is 0.001g, answer the following questions:

(i) Whose measurement is both accurate and precise? Justify your answer.

(ii) Whose measurement is precise and not accurate Justify your answer?

(iii) Whose measurements are neither accurate nor precise? Justify your answer.

(iv)  Mention the associated value or values with these observations.

Question. An organic compound on analysis was found to contain 0.032% of sulphur. The molecular mass of the compound, if its molecule contain two sulphur atom, is
a. 200
b. 2000
c. 20000
d. 200000
Answer : D

Question. Vapour density of a volatile substance is 4 in comparison to methane. Its molecular mass will be
a. 8
b. 2
c. 64
d. 128
Answer : C

Question. 4.6×10²² atoms of an element weight 13.8 g. the atomic mass of the element is
a. 290
b. 180
c. 34.4
d. 10.4
Answer : B

Question. The total number of protons in 10 g of calcium carbonate is
a. 3.0115×10²⁴
b. 1.5057×10²⁴
c. 2.0478×10²⁴
d. 4.0956×10²⁴
Answer : A

Question. 19.7 kg of gold was recovered from smuggler. The atoms of gold recovered are (Au=197)
a. 100
b. 6.02×10²³
c. 6.02×10²⁴
d. 6.02×10²⁵
Answer : D

Question. The density of air is 0.001293𝑔𝑚𝐿⁻¹. Its vapour density is
a. 143
b. 14.3
c. 1.43
d. 0.143
Answer : D

Question. The vapour density of two gases are in the ratio of 1 : 3. Their molecular mass are in the ratio of
a. 1 : 3
b. 1 : 2
c. 2 : 3
d. 3 : 1
Answer : A

Question. The total number of atoms of all element present in 1 mole of ammonium dichromate (𝑁𝐻₄)₂𝐶𝑟₂𝑂₇ is:
a. 19
b. 6.02×10²³
c. 114.437×10²³
d. 84.322×10²³
Answer : C

Question. The maximum number of molecules is present in
a. 15 L of 𝐻₂ at STP
b. 5 L of 𝑁₂ at STP
c. 0.5 L of 𝐻₂ gas
d. 10 g of 𝑂₂ gas
Answer : A

Question. Assuming fully decomposed, the volume of 𝐶𝑂₂ released at STP on heating 9.85 g of 𝐵𝑎𝐶𝑂₃ wiil be
a. 0.84 L
b. 2.24 L
c. 4.06 L
d. 1.12 L
Answer : D

Question. The number of moles of oxygen in one litre of air containing 21% oxygen by volume, in standard conditions,
a. 0.186 mole
b. 0.21 mole
c. 2.10 mole
d. 0.0093 mole
Answer : D

Question. The maximum amount of 𝐵𝑎𝑆𝑂4 that can be obtained on mixing 0.5 mole 𝐵𝑎𝐶𝑙₂ with 1 mole 𝐻₂𝑆𝑂₄ is
a. 0.5mol
b. 0.1mol
c. 0.15mol
d. 0.2mol
Answer : A

Question. How many grams of dibasic acid (Mol. Mass 200 ) should be present in 100 mL of solution to give 0.1 normality?
a. 1 g
b. 2 g
c. 10 g
d. 20 g
Answer : A

Question. The weight of iron which will be converted into its oxide (𝐹𝑒₃𝑂₄) by the action of 18 g of stream on it will be (Atomic mass of 𝐹𝑒=56)
a. 168 g
b. 84 g
c. 42 g
d. 21 g
Answer : C

Question. How many moles of lead(II) chloride will be formed from a reaction between 6.5 g 𝑃𝑏𝑂 and 3.2 g 𝐻𝐶𝑙
a. 0.011
b. 0.029
c. 0.044
d. 0.333
Answer : B

Question. What volume of oxygen gas (𝑂₂)measured at 0°𝐶 and 1 atm is needed to burn completely 1 L of propane gas measured under the same condition
a. 5L
b. 10L
c. 7L
d. 6L
Answer : A

Question. In an experiment 4 g of 𝑀₂𝑂_𝑥 oxide was reduced to 2.8 g of the metal. If the atomic mass of the metal is 56g/mol the number of oxygen atom in the oxide
a. 1
b. 2
c. 3
d. 4
Answer : C

Question. The reaction given below
𝐶𝑎+2𝐻₂𝑂 →𝐶𝑎(𝑂𝐻)₂+𝐻₂
What volume of 𝐻₂ at STP woukd be liberated when 8 g of calcium completely reacts with water?
a. 0.2 𝑐𝑚³
b. 0.4 𝑐𝑚³
c. 224 𝑐𝑚³
d. 4480 𝑐𝑚³
Answer : D

Question. 20 kg of 𝑁2 and 3 kg of 𝐻₂ are mixed to produce 𝑁𝐻₃(g) The amount of 𝑁𝐻₃(g) formed is
a. 17 kg
b. 34 kg
c. 20 kg
d. 3 kg
Answer : A

Question. If a compound on analysis was found to contain C=18.5%, H=1.55%, Cl=55.04% and O=24.81%, then its empirical formula is
a. 𝐶₂𝐻₂𝑂𝐶𝑙
b. 𝐶𝐻₂𝐶𝑙𝑂
c. 𝐶𝐻𝐶𝑙𝑂
d. 𝐶𝑙𝐶𝐻₂𝑂
Answer : C

Question. A metallic oxide contain 60% of the metal. The equivalent weight of the metal is
a. 12
b. 24
c. 40
d. 48
Answer : A

Question. For a given reaction
4𝐻𝐶𝑙+ 𝑀𝑛𝑂₂ →𝑀𝑛𝐶𝑙₂+ 𝐶𝑙₂
How many grams of HCl will react with 5 g of manganese dioxide?
a. 6.4 g HCl
b. 4.8 g HCl
c. 8..4 g HCl
d. 7.2 g HCl
Answer : C

Question. The mass and charge of one mole electrons respectively is
a. 54.8×10⁻⁷𝑘𝑔,9.65×10⁴𝑐𝑜𝑢𝑙𝑜𝑚𝑏
b. 5.48×10⁻⁷𝑘𝑔,9.65×10³ 𝑐𝑜𝑢𝑙𝑜𝑚𝑏
c. 5.48×10⁻⁷𝑔,9.65×10⁴ 𝑐𝑜𝑚𝑙𝑜𝑚𝑏
d. 5.48×10⁻⁷𝑘𝑔,9.65×10⁴ 𝑐𝑜𝑚𝑙𝑜𝑚𝑏
Answer : D

Question. A mixture of 2.3 g formic acid and 4.5 g oxalic acid is treated with conc.𝐻₂𝑆𝑂₄. The evolved gaseous mixture is passed over KOH pellets. Weight(in g) of the remaining gaseous product at STP will be
a. 4.4
b. 1.4
c. 2.8
d. 3.0
Answer : C

Question. 3 g of a hydrocarbon on combustion in excess of oxygen produce 8.8 g of 𝐶𝑂₂ and 5.4 g of 𝐻₂𝑂. The data illustrate the law of
a. Conservation of mass
b. Multiple proportion
c. Constant proportion
d. Reciprocal proportion
Answer : A

Question. 5 g sample contain only Na₂CO₃ and Na₂SO₄. This sample is dissolved and the volume made up to 250 mL. 25 mL of this solution neutralizes 20 mL of 0.1 M H₂SO₄. Calculate the % of Na₂SO₄ in the sample.
(a) 42.4
(b) 57.6
(c) 36.2
(d) 0.576
Answer : B

Question. 1 mole of equimolar mixture of ferric oxalate and ferrous oxalate requires x mole of KMnO4 in acidic medium for complete oxidation. x is:
(a) 0.5 mole
(b) 0.9 mole
(c) 1.2 mole
(d) 4.5 mole
Answer : B

Question. Two solutions of a substance (non electrolyte) are mixed in the following manner. 480 mL of 1.5 M first solution + 520 mL of 1.2 M second solution. What is the molarity of the final mixture?
(a) 2.70 M
(b) 1.344 M
(c) 1.50 M
(d) 1.20 M
Answer : B

Numeric Value Answer

Question. A mixture of HCOOH and H₂C₂O₄ is heated with concentrated H₂SO₄. The gas produced is collected and on treating with KOH solution, the volume of gas decreases by one-sixth. Calculate the molar ratio of the two acids (HCOOH : H₂C₂O₄) in the original mixture.
Answer : 4

Question. The minimum number of moles of O₂ required for complete combustion of 1 mole of propane and 2 moles of butane is ______.
Answer : 18

Question. A 0.276 g impure sample of copper ore is dissolved and Cu²⁺ is titrated with KI solution. I2 liberated required 40 mL of 0.1M Na₂S₂O₃ solution for titration. What is the % of impurities in the ore?
Answer : 8

Question. How much volume of 4.0 M HNO₃ is required to prepare 60 mL of 0.2 M HNO₃ from a stock solution of 4.0 M HNO₃?
Answer : 3

Question. A 16.24 mL sample of vinegar of density 1.06 g/ mL required 48.24 mL of 0.36 N solution of a standard alkali. Determine percentage weight of acetic acid in vinegar.
Answer : 6

Question. Density of a sulphuric acid solution is 1.225g/ mL. and it is 40% H₂SO₄ by weight. Determine molarity of this solution.
Answer : 5

Question. A mixture contains 1.0 mole each of NaOH, Na₂CO₃ and NaHCO3. When half of mixture is titrated with HCl, it required x mole of HCl in presence of phenolphthalein. In another experiment, half of mixture required y mole of same HCl in presence of methyl orange. Find the value of (x + y).
Answer : 3

Question. One gram of a metallic chloride was found to contain 0.835 g of chlorine. Its vapour density is 85.5. If its molecular formula is MxCly, then what is value of (x + y)?
Answer : 5

Question. 0.7875 g of crystalline barium hydroxide is dissolved in water. For the neutralization of this solution 20 mL of N/4 HNO₃ is required. How many moles of water of crystallization are present in one mole of this base? (Given : Atomic mass Ba = 137, O = 16, N = 14, H = 1)
Answer : 8
 

Question. How much volume of sulphur dioxide at STP will be obtained by completely burning 10 g of pure sulphur?
Answer : 7
 

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