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Free Fundamental Concepts of Chemistry MCQs with Answers

894 Fundamental Concepts of Chemistry MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Mole calculations connect mass, number of particles and Avogadro's number, while balanced equations provide the mole ratios used in stoichiometry. Questions cover limiting and excess reactants, theoretical yield and percentage yield, including identifying which reactant is consumed first and comparing the actual product with the maximum possible product.

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Moles and Avogadro's NumberLimiting and Excess ReactantsTheoretical and Percentage Yield
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894 questions · page 11 of 45

201. In which gaseous equilibrium more product will be formed by decreasing pressure

  • A. N2+3H2 ⇌ 2NH3
  • B. PCl5 ⇌PCl3 +Cl2
  • C. 2SO2 + O2 ⇌ 2SO3
  • D. 2H2 + O2 ⇌ 2H2O

Explanation: According to Le Chatelier's principle, when a stress is applied to a system at equilibrium, the system will respond in a way that tries to…

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Correct answer: 2SO2 + O2 ⇌ 2SO3

202. For the reaction 2SO2+O2⇌2SO3

  • A. Kp=Kc
  • B. Kp > Kc
  • C. Kp < Kc
  • D. Kc=0 but Kp is not zero

Explanation: The correct option for the relationship between Kp and Kc for the reaction 2SO2 + O2 ⇌ 2SO3 is:d.

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Correct answer: Kc=0 but Kp is not zero

203. Bromine has two isotopes having the relative abundance as "Bras 50.51% and Bras = 49.49%.the average atomic mass of bromine is

  • A. 81
  • B. 80
  • C. 79.5
  • D. 79

Explanation: In summary, option c (79.5) is the correct answer based on the weighted average of the isotopes considering their relative abundances.

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Correct answer: 79.5

204. 1 mole of CH1 contains

  • A. 6.02 x 10^23 atoms of H
  • B. 4 g-atom of hydrogen
  • C. 1.81 x 10^2 molecules of CH
  • D. 3.0 g of carbon

Explanation: The chemical formula CH1 represents one mole of methane. Methane (CH4) is composed of one carbon atom (C) and four hydrogen atoms (H).1…

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Correct answer: 6.02 x 10^23 atoms of H

205. How many moles of helium gas occupy 22.41 at 0°C at 1 atm. Pressure

  • A. 011
  • B. 0.90
  • C. 1.0
  • D. 1.11

Explanation: To find the number of moles of a gas, you can use the ideal gas law equation:PV=nRTWhere:● P is the pressure of the gas (in atm),● V is…

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Correct answer: 1.0

206. All of the following statements are incorrect for 20 moles of hydrogen per oxide except is has

  • A. 80 mole of atoms
  • B. 30 moles of Oxygen atoms
  • C. 30 moles of hydrogen atoms
  • D. 20 moles of hydrogen atoms

Explanation: This statement is correct. For 20 moles of hydrogen peroxide (H₂O₂), it would indeed have 20 moles of hydrogen atoms.

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Correct answer: 20 moles of hydrogen atoms

207. An X gram of calcium carbonate was completely burnt in air. The weight of the solid residue formed is 28 g. what is the value of X in grams

  • A. 44
  • B. 200
  • C. 150
  • D. 50

Explanation: Calcium carbonate decomposition: When calcium carbonate (CaCO₃) is heated strongly in air, it decomposes according to the following…

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Correct answer: 50

208. What is the concentration of nitrate ions, if equal volumes of 0.1M AgNO, and 0.1M NaCl are mixed together?mol

  • A. 0.1M
  • B. 0.2M
  • C. 0.05M
  • D. 0.25M

Explanation: When AgNO₃ (silver nitrate) and NaCl (sodium chloride) are mixed, a double displacement reaction occurs, leading to the formation of AgCl…

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Correct answer: 0.05M

209. The volume in litters of CO2 liberated at STP when 10 grams of 90% pure limestone is heated completely is

  • A. 22.4
  • B. 2.24
  • C. 20.16
  • D. 2.016

Explanation: The correct answer is d. 2.016 L.Calculation:Calculate the amount of pure limestone in the sample:○ Given purity = 90%○ Total mass = 10 g○…

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Correct answer: 2.016

210. Law of mass action determines

  • A. Only products
  • B. Composition of reacting substances and products
  • C. Only reacting substances
  • D. None of the above

Explanation: The law of mass action is a fundamental principle that relates the concentrations of reactants and products in a chemical reaction at…

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Correct answer: Composition of reacting substances and products

211. 100g of CaCO, is treated with 1 liter of 1 NHCI. What would be the weight of CO2 liberated after the completion of the reaction

  • A. 5.5g
  • B. 11g
  • C. 22g
  • D. 33g

Explanation: Let's perform the calculations:Molar mass of CACO3=40.08+12.01+(3×16.00)Moles of CaCO3 =100/40.08+12.01+(3×16.00)Moles of CO2 =Moles of…

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Correct answer: 22g

212. What is empirical formula of glucose

  • A. CH2O
  • B. CH
  • C. C6H12O6
  • D. CHO

Explanation: Molecular formula of glucose is C6H12O6.Therefore, the empirical formula of glucose is CH2O

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Correct answer: CH2O

213. In the reaction 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O. What is the equivalent weight of HNO₃? (If the molecular weight of HNO₃ is M).

  • A. M
  • B. M/3
  • C. 3/4 M
  • D. 4/3 M

Explanation: The n-factor for HNO₃ in the overall reaction is the total electrons transferred (6) divided by the moles of HNO₃ used (8), which equals…

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Correct answer: 4/3 M

214. A carbon compound containing carbon and oxygen has an approximate molar mass of 290. On analysis, it is found to contain 50% by mass of each element. The molecular formula of the compound is:

  • A. C₁₂O₉
  • B. C₄O₃
  • C. C₃O₄
  • D. C₉O₁₂

Explanation: From the 50% mass data, the empirical formula is found to be C₄O₃ (mass = 96 g/mol).

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Correct answer: C₁₂O₉

215. NH₃ is produced according to the following reaction: N₂(g) + 3H₂(g)→ 2NH₃(g). In an experiment, 0.25 mol of NH₃ is formed when 0.5 mol of N₂ is reacted with 0.5 mol of H₂. What is the % yield?

  • A. 75%
  • B. 50%
  • C. 33%
  • D. 25%

Explanation: With the given reactants, H₂ is the limiting reactant. The theoretical yield of NH₃ from 0.5 mol of H₂ is 0.333 mol.

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Correct answer: 75%

216. Caffeine has a molecular mass of 194. If it contains 28.9% by mass of nitrogen, the number of atoms of nitrogen in one molecule of caffeine is:

  • A. 4
  • B. 6
  • C. 2
  • D. 3

Explanation: The total mass of nitrogen in one mole of caffeine is 0.289 × 194 ≈ 56.06 g.

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Correct answer: 4

217. 12g carbon combines with 64g sulfur to produce CS₂. 12g carbon also combines with 32g oxygen to form CO₂. 10g sulfur combines with 10 g oxygen to produce SO₂. These data illustrate the:

  • A. Law of multiple proportions
  • B. Law of definite proportions
  • C. Law of reciprocal proportions
  • D. Law of gaseous volumes

Explanation: This demonstrates the Law of Reciprocal Proportions. The ratio of masses of S and O that combine with a fixed mass of C is 64:32 (or 2:1).

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Correct answer: Law of reciprocal proportions

218. The number of moles of Cr₂O₇ ²⁻ needed to oxidize 0.136 equivalents of N₂H₅ ⁺ according to the reaction N₂H₅ ⁺ + Cr₂O₇ ²⁻ → N₂ + Cr³⁺ + H₂O is:

  • A. 0.136
  • B. 0.272
  • C. 0.816
  • D. 0.0227

Explanation: In this reaction, the n-factor for Cr₂O₇²⁻ is 6, as each of the two Cr atoms gains 3 electrons.

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Correct answer: 0.0227

219. In the balanced equation for the combustion of pentane, C₅H₁₂(g) + _ O₂(g) → 5CO₂(g) + 6H₂O(l), the coefficient of the oxygen should be:

  • A. 16
  • B. 12
  • C. 11
  • D. 8

Explanation: After balancing carbon (5CO₂) and hydrogen (6H₂O), the product side has (5×2) + 6 = 16 oxygen atoms.

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Correct answer: 8

220. 11.2L of CO₂ at STP corresponds to how many moles?

  • A. 0.5
  • B. 0.3
  • C. 0.2
  • D. 0.1

Explanation: At STP, one mole of any ideal gas occupies 22.4 L. Therefore, the number of moles is the given volume divided by the molar volume: 11.2 L…

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Correct answer: 0.5
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