Some Basic Concepts of Chemistry

33 NEET-UG practice questions on Some Basic Concepts of Chemistry, part of Chemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 10 mL mixture of CH₄ and C₂H₆ burns completely in excess oxygen and gives 14 mL of CO₂. All volumes are at the same temperature and pressure. Find the volume of O₂ consumed.
1. A35 mL
2. B26 mL
3. C20 mL
4. D28 mL
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Answer: B · 26 mL
Let CH₄ = x and C₂H₆ = y: x + y = 10 and x + 2y = 14, so y = 4 mL and x = 6 mL. Oxygen used = 6 × 2 + 4 × 3.5 = 26 mL. Check by atoms: 14 CO₂ need 28 O, and 48 H give 24 H₂O needing 24 O, a total of 52 O = 26 O₂.
- A: This treats the whole mixture as C₂H₆.
- C: This treats the whole mixture as CH₄.
- D: This counts the oxygen in CO₂ only and forgets the oxygen in the water formed.
Remember this
At the same temperature and pressure, gas volumes combine in the mole ratio of the equation (Gay-Lussac's law).
Question 2 · Medium
Ethanol (23 g) is dissolved in water (54 g). What is the mole fraction of ethanol in this solution? (C₂H₅OH = 46, H₂O = 18)
1. A0.143
2. B0.167
3. C0.857
4. D0.299
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Answer: A · 0.143
Ethanol = 23/46 = 0.5 mol and water = 54/18 = 3 mol. Mole fraction of ethanol = 0.5/(0.5 + 3) = 1/7 = 0.143.
- B: This divides by the moles of water alone, not the total moles.
- C: This is the mole fraction of water.
- D: This is the mass fraction of ethanol, 23/77.
Remember this
Mole fraction divides by the total moles of all components, and the fractions in a solution add up to 1.
Question 3 · Easy
Which concentration term of a solution changes with temperature?
1. AMolality
2. BMolarity
3. CMass per cent
4. DMole fraction
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Answer: B · Molarity
Molarity is moles per litre of solution, and the volume of a solution changes with temperature. The other three are built only from masses or moles, which do not change on heating.
- A: Molality uses the mass of solvent, which does not change with temperature.
- C: Mass per cent is a ratio of masses, which does not change with temperature.
- D: Mole fraction is a ratio of moles, which does not change with temperature.
Remember this
A concentration term that has volume in it depends on temperature; a term based only on mass or moles does not.
Question 4 · Medium
An organic liquid contains 54.5% C, 9.1% H and 36.4% O by mass, and its molar mass is 88 g/mol. Identify its molecular formula. (C = 12, H = 1, O = 16)
1. AC₅H₁₂O
2. BC₃H₄O₃
3. CC₄H₈O₂
4. DC₂H₄O
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Answer: C · C₄H₈O₂
Dividing by atomic masses gives C 4.54, H 9.1 and O 2.275, a ratio of 2:4:1, so the empirical formula is C₂H₄O with mass 44. Since 88/44 = 2, the molecular formula is C₄H₈O₂.
- A: This also has mass 88 but does not fit the 2:4:1 atom ratio.
- B: This has mass 88 but does not fit the 2:4:1 atom ratio.
- D: This is the empirical formula, with mass 44 rather than 88.
Remember this
Molecular formula = empirical formula × (molar mass / empirical formula mass).
Question 5 · Hard
An aqueous NaOH solution is 2 M and has a density of 1.08 g/mL. Calculate its molality. (NaOH = 40)
1. A1.85 m
2. B2.00 m
3. C1.72 m
4. D2.16 m
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Answer: B · 2.00 m
One litre of solution has a mass of 1080 g and contains 2 × 40 = 80 g of NaOH, so the water is 1000 g = 1 kg. Molality = 2 mol / 1 kg = 2.00 m. Check by formula: m = M/(d − M × molar mass/1000) = 2/(1.08 − 0.08) = 2.
- A: This divides by the solution mass, forgetting to remove the solute.
- C: This adds the solute mass to the solution mass instead of subtracting it.
- D: This multiplies molarity by density instead of finding the solvent mass.
Remember this
For molality, subtract the solute mass from the solution mass; the density alone does not give the solvent mass.
Question 6 · Medium
Arrange the following samples in increasing order of the total number of atoms present. (H = 1, He = 4, N = 14, O = 16) A. 4 g of He B. 9 g of H₂O C. 28 g of N₂ D. 8 g of O₃
1. AD, B, A, C
2. BC, B, A, D
3. CA, D, B, C
4. DD, A, B, C
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Question 7 · Easy
A sample of methane, CH₄, has a mass of 8 g. How many moles of hydrogen atoms does it contain? (C = 12, H = 1)
1. A2 mol
2. B0.5 mol
3. C1 mol
4. D4 mol
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Question 8 · Easy
Count the significant figures in the measured length 0.02040 m.
1. A6
2. B3
3. C5
4. D4
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Question 9 · Medium
Given below are two statements: Statement I: The mole fraction of a component in a solution has no units and does not depend on temperature. Statement II: The molarity of an aqueous solution increases when the solution is warmed. Choose the correct answer.
1. AStatement I is incorrect but Statement II is correct
2. BStatement I is correct but Statement II is incorrect
3. CBoth Statement I and Statement II are correct
4. DBoth Statement I and Statement II are incorrect
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Question 10 · Medium
Aluminium (10.8 g) is heated with chlorine (21.3 g) until the reaction stops: 2Al + 3Cl₂ → 2AlCl₃ What mass of AlCl₃ forms? (Al = 27, Cl = 35.5)
1. A26.7 g
2. B53.4 g
3. C32.1 g
4. D40.05 g
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Question 11 · Medium
Butane burns completely in oxygen: a C₄H₁₀ + b O₂ → c CO₂ + d H₂O For the balanced equation in the lowest whole numbers, what are a, b, c and d, in that order?
1. A2, 13, 8, 10
2. B2, 13, 8, 5
3. C1, 9, 4, 5
4. D1, 13, 4, 5
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Question 12 · Hard
Strong heating of an 18.4 g mixture of CaCO₃ and MgCO₃ decomposes both carbonates completely to their oxides and gives 8.8 g of CO₂. What mass of CaCO₃ was in the mixture? (Ca = 40, Mg = 24, C = 12, O = 16)
1. A9.2 g
2. B8.4 g
3. C16.8 g
4. D10 g
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Question 13 · Medium
Concentrated hydrochloric acid in a laboratory bottle is 36.5% HCl by mass and has a density of 1.2 g mL⁻¹. Its molarity is (HCl = 36.5 g mol⁻¹)
1. A14.4 M
2. B10 M
3. C12 M
4. D15.7 M
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Question 14 · Medium
A chemist mixes 100 mL of 0.3 M HCl with 200 mL of 0.6 M HCl. Assuming the volumes are additive, the molarity of the mixture is
1. A0.45 M
2. B0.9 M
3. C0.5 M
4. D0.75 M
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Question 15 · Easy
Limestone is mainly calcium carbonate, CaCO₃. What is the mass per cent of calcium in pure CaCO₃? (Ca = 40, C = 12, O = 16)
1. A60%
2. B12%
3. C40%
4. D48%
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Question 16 · Medium
A sealed vessel holds 28 g of N₂ and 3 g of H₂. They react by N₂ + 3H₂ → 2NH₃ until one reactant is used up. Which reactant is left over, and how much of it remains? (N = 14, H = 1)
1. A7 g of N₂
2. B14 g of N₂
3. C1 g of H₂
4. DNone; both are used up exactly
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Question 17 · Medium
A laboratory sample of sulphuric acid is 49% H₂SO₄ by mass and has a density of 1.5 g mL⁻¹. What is its molarity? (H₂SO₄ = 98 g mol⁻¹)
1. A7.5 M
2. B9.8 M
3. C3.3 M
4. D5.0 M
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Question 18 · Hard
An organic compound contains only carbon, hydrogen and oxygen. Complete combustion of 0.30 g of it gives 0.44 g of CO₂ and 0.18 g of H₂O, and its vapour density is 30. What is its molecular formula? (C = 12, H = 1, O = 16)
1. AC₂H₄O₂
2. BC₄H₈O₄
3. CC₃H₈O
4. DCH₂O
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Question 19 · Easy
A sample of carbon dioxide weighs 4.4 g. How many molecules of CO₂ does it contain? (C = 12, O = 16, N_A = 6.0 × 10²³ mol⁻¹)
1. A2.6 × 10²⁴
2. B1.8 × 10²³
3. C6.0 × 10²³
4. D6.0 × 10²²
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Question 20 · Medium
Magnesium ribbon (6.0 g) is burnt in a closed vessel containing 8.0 g of oxygen gas: 2Mg + O₂ → 2MgO What mass of magnesium oxide forms when the limiting reagent is used up? (Mg = 24, O = 16)
1. A14 g
2. B5 g
3. C20 g
4. D10 g
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Question 21 · Medium
Given below are two statements: Statement I: Hydrogen combines with oxygen to form water and hydrogen peroxide; for a fixed mass of hydrogen, the masses of oxygen in these two compounds are in the ratio 1 : 2. Statement II: At the same temperature and pressure, 1 volume of nitrogen reacts with 3 volumes of hydrogen to give 2 volumes of ammonia, in line with Gay Lussac's law of gaseous volumes. Choose the correct answer.
1. ABoth Statement I and Statement II are correct
2. BStatement I is correct but Statement II is incorrect
3. CBoth Statement I and Statement II are incorrect
4. DStatement I is incorrect but Statement II is correct
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Question 22 · Hard
When 10 mL of a gaseous hydrocarbon is burnt completely, it uses 55 mL of oxygen and gives 40 mL of carbon dioxide, all volumes being measured at the same temperature and pressure. How many hydrogen atoms are there in one molecule of the hydrocarbon?
1. A10
2. B22
3. C3
4. D6
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Question 23 · Medium
When 100 mL of 0.20 M AgNO₃ is mixed with 100 mL of 0.10 M NaCl, silver chloride precipitates. What mass of AgCl forms? (AgCl = 143.5 g mol⁻¹)
1. A14.35 g
2. B2.870 g
3. C0.7175 g
4. D1.435 g
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Question 24 · Easy
One atomic mass unit (u) is defined as exactly
1. Aone-twelfth of the mass of one carbon-12 atom
2. Bthe mass of one proton
3. Cthe mass of one hydrogen-1 atom
4. Done-sixteenth of the mass of one oxygen-16 atom
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Question 25 · Easy
What is the mass of 0.25 mol of glucose, C₆H₁₂O₆? (C = 12, H = 1, O = 16)
1. A7.5 g
2. B720 g
3. C45 g
4. D4.5 g
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8 more Some Basic Concepts of Chemistry questions

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Some Basic Concepts of Chemistry

A 10 mL mixture of CH₄ and C₂H₆ burns completely in excess oxygen and gives 14 mL of CO₂. All volumes are at the same temperature and pressure. Find the volume of O₂ consumed.

Ethanol (23 g) is dissolved in water (54 g). What is the mole fraction of ethanol in this solution? (C₂H₅OH = 46, H₂O = 18)

Which concentration term of a solution changes with temperature?

An organic liquid contains 54.5% C, 9.1% H and 36.4% O by mass, and its molar mass is 88 g/mol. Identify its molecular formula. (C = 12, H = 1, O = 16)

An aqueous NaOH solution is 2 M and has a density of 1.08 g/mL. Calculate its molality. (NaOH = 40)

Arrange the following samples in increasing order of the total number of atoms present. (H = 1, He = 4, N = 14, O = 16) A. 4 g of He B. 9 g of H₂O C. 28 g of N₂ D. 8 g of O₃

A sample of methane, CH₄, has a mass of 8 g. How many moles of hydrogen atoms does it contain? (C = 12, H = 1)

Count the significant figures in the measured length 0.02040 m.

Given below are two statements: Statement I: The mole fraction of a component in a solution has no units and does not depend on temperature. Statement II: The molarity of an aqueous solution increases when the solution is warmed. Choose the correct answer.

Aluminium (10.8 g) is heated with chlorine (21.3 g) until the reaction stops: 2Al + 3Cl₂ → 2AlCl₃ What mass of AlCl₃ forms? (Al = 27, Cl = 35.5)

Butane burns completely in oxygen: a C₄H₁₀ + b O₂ → c CO₂ + d H₂O For the balanced equation in the lowest whole numbers, what are a, b, c and d, in that order?

Strong heating of an 18.4 g mixture of CaCO₃ and MgCO₃ decomposes both carbonates completely to their oxides and gives 8.8 g of CO₂. What mass of CaCO₃ was in the mixture? (Ca = 40, Mg = 24, C = 12, O = 16)

Concentrated hydrochloric acid in a laboratory bottle is 36.5% HCl by mass and has a density of 1.2 g mL⁻¹. Its molarity is (HCl = 36.5 g mol⁻¹)

A chemist mixes 100 mL of 0.3 M HCl with 200 mL of 0.6 M HCl. Assuming the volumes are additive, the molarity of the mixture is

Limestone is mainly calcium carbonate, CaCO₃. What is the mass per cent of calcium in pure CaCO₃? (Ca = 40, C = 12, O = 16)

A sealed vessel holds 28 g of N₂ and 3 g of H₂. They react by N₂ + 3H₂ → 2NH₃ until one reactant is used up. Which reactant is left over, and how much of it remains? (N = 14, H = 1)

A laboratory sample of sulphuric acid is 49% H₂SO₄ by mass and has a density of 1.5 g mL⁻¹. What is its molarity? (H₂SO₄ = 98 g mol⁻¹)

An organic compound contains only carbon, hydrogen and oxygen. Complete combustion of 0.30 g of it gives 0.44 g of CO₂ and 0.18 g of H₂O, and its vapour density is 30. What is its molecular formula? (C = 12, H = 1, O = 16)

A sample of carbon dioxide weighs 4.4 g. How many molecules of CO₂ does it contain? (C = 12, O = 16, N_A = 6.0 × 10²³ mol⁻¹)

Magnesium ribbon (6.0 g) is burnt in a closed vessel containing 8.0 g of oxygen gas: 2Mg + O₂ → 2MgO What mass of magnesium oxide forms when the limiting reagent is used up? (Mg = 24, O = 16)

When 10 mL of a gaseous hydrocarbon is burnt completely, it uses 55 mL of oxygen and gives 40 mL of carbon dioxide, all volumes being measured at the same temperature and pressure. How many hydrogen atoms are there in one molecule of the hydrocarbon?

When 100 mL of 0.20 M AgNO₃ is mixed with 100 mL of 0.10 M NaCl, silver chloride precipitates. What mass of AgCl forms? (AgCl = 143.5 g mol⁻¹)

One atomic mass unit (u) is defined as exactly

What is the mass of 0.25 mol of glucose, C₆H₁₂O₆? (C = 12, H = 1, O = 16)