250+ TOP MCQs on Stoichiometry and Stoichiometric Calculations and Answers

Chemistry Multiple Choice Questions on “Stoichiometry and Stoichiometric Calculations”.

1. In a particular reaction, one of the reactants limits the number of products formed. That is called as _______
a) Limiting reagent
b) Limiting product
c) Excessive reagent
d) Excessive reactant
Answer: a
Clarification: Though the other substances are excess in amount than the required, each and every reactant needs to be in a fixed ratio to attain the desired product. So, thereby, the reactant that limits the quantity of the product formed is called limiting reagent and this reactant gets consumed first completely.

2. Which of the following is not true regarding balanced chemical equations?
a) They contain the same number of atoms on each side
b) Electrons are also balanced
c) An equal number of molecules on both the side
d) Follows the law of conservation of mass
Answer: c
Clarification: A balanced reaction may not have an equal number of molecules on both the sides, because molecules may combine into one or a single molecule may breakdown into two or more. IT can disassociate or undergo double decomposition.

3. Which of the given reactions are counted as balanced reactions?
a) H₂ + O₂ → 2H₂O
b) 4Al + 3O₂ → 2Al₂O₃
c) Mg(OH)₂ + 2HNO₃ → 2Mg(NO₃)₂ + 2H₂O
d) N₂ + 3H₂ → NH₃
Answer: b
Clarification: 4Al + 3O₂ → 2Al₂O₃ is a balanced reaction because the number of atoms of different elements on both sides is equal. The correctly balanced equations of the rest are 2H₂ + O₂ → 2H₂O; Mg(OH)₂ + 2HNO₃ → Mg(NO₃)₂ + 2H₂O and N₂ + 3H₂ → 2NH₃.

4. What is the amount of water produced when 8g of hydrogen is reacted with 32g of oxygen?
a) 2moles
b) 1mole
c) 3 moles
d) 0.5mole
Answer: a
Clarification: The chemical equation of water formation is 2H₂ + O₂ → 2H₂O. Though we have 8g of hydrogen, here oxygen is the limiting reagent. So the only 4g of hydrogen can be used to produce water i.e. 36g of water. That is 2 moles.

5. Calculate the mass percent of magnesium in the formation of magnesium oxide.
a) 0.3
b) 1.5
c) 0.67
d) 0.6
Answer: d
Clarification: The chemical equation of formation of magnesium oxide is 2 Mg_(s) + O_2(g) ® 2MgO_(s). The formula for calculation of mass percent is (mass of solute/mass of solution) x 100. Therefore 2(24)/2(24+16) = 0.6.

6. A and B are two solutions that are mixed. Calculate the resultant solution’s molarity.

a) 0.8 mol/L
b) 0.88 mol/L
c) 1.3 mol/L
d) 1.05 mol/L
Answer: b
Clarification: When two solutions are combined, the resultant molarity is M₁V₁ + M₂V₂/V₁ + V₂. Consider M₁ = 1.3, M₂ = 0.8, V₁ = 100ml and V₂ = 500ml. Now resultant molarity = 1.3(100) + 0.8(500)/100 + 500 = 0.88 mol/L.

7. A solution contains 8 moles of solute and the mass of the solution is 4 kg. What’s the molality of this solution?
a) 5 mol/kg
b) 8 mol/kg
c) 4 mol/kg
d) 0.5 mol/kg
Answer: d
Clarification: Molality of a solution is given y the formula; molality = number of moles of the solute/mass of the solution. So here the number of moles is 8 and the mass of the solution is 4 kg. Molality is 8/4 = 0.5 mol/kg.

8. In a container, there are 4 moles of nitrogen, 3 moles of oxygen and 7 moles of hydrogen; find out the mole fraction of oxygen in this reaction.
a) 0.2143
b) 0.2142
c) 0.1234
d) 0.2434
Answer: a
Clarification: Mole fraction of a substance is given by the formula: Mole fraction = No. of moles of that substances/No. of total moles of solution. Mole fraction of oxygen here = 3/4 + 3 + 7 = 3/14 = 0.2143.

9. Find the amount of carbon dioxide produced by the combustion of 20g of methane.
a) 44g
b) 20g
c) 66g
d) 22g
Answer: c
Clarification: The chemical balanced equation for combustion of methane is CH_4(g) + 2O_2(g) →CO_2(g) + 2H₂O_(g). From the above equation, 1 mole of methane gives 1 mole of carbon dioxide. But 20g of methane = 1.25 moles, therefore it gives 1.25 moles of carbon dioxide = 44(1.5) = 66g.

10. What’s the balanced equation of CO₂ + H₂O → C₆H₁₂O₆ + O₂?
a) CO₂ + H₂O → C₆H₁₂O₆ + O₂
b) 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂
c) 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 2 O₂
d) 3 CO₂ + 2H₂O → C₆H₁₂O₆ + O₂
Answer: b
Clarification: 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂ is the balanced equation because the number of atoms of different elements is the same on both sides. Rest of them do not have an equal number of atoms of different elements on both sides.