Stoichiometry and Stoichiometric Calculations - UNSOLVED PRACTICE SET
Chapter: Some Basic Concepts of Chemistry | Topic: Stoichiometry and Stoichiometric Calculations
STOICHIOMETRY AND STOICHIOMETRIC CALCULATIONS - UNSOLVED PRACTICE SET
Topic: Stoichiometry and Stoichiometric Calculations
Multiple Choice Questions
Q1. Stoichiometry deals with:
- The rate of chemical reactions
- The quantitative relationships between reactants and products
- The mechanism of chemical reactions
- The energy changes in chemical reactions
Q2. In the reaction N₂ + 3H₂ → 2NH₃, the stoichiometric coefficient of hydrogen is:
- 1
- 2
- 3
- 6
Q3. According to the balanced equation 2H₂ + O₂ → 2H₂O, 4 g of hydrogen reacts with:
- 4 g of oxygen
- 16 g of oxygen
- 32 g of oxygen
- 8 g of oxygen
Q4. If 2 moles of A react with 3 moles of B to form 2 moles of C, then the mass of C formed from 1 mole of A depends on:
- The molar mass of C
- The volume of the reaction vessel
- The temperature of the reaction
- The catalyst used
Q5. The amount of product actually obtained in a chemical reaction is called:
- Theoretical yield
- Actual yield
- Percentage yield
- Stoichiometric yield
Q6. In a balanced chemical equation, the number of atoms of each element:
- Can be different on both sides
- Must be the same on both sides
- Is always greater on the product side
- Depends on the reaction conditions
Short Answer Questions
Q7. What is a balanced chemical equation? Why must chemical equations be balanced before stoichiometric calculations?
Q8. Define theoretical yield and actual yield. What is percentage yield?
Q9. In the reaction CaCO₃ → CaO + CO₂, how many grams of calcium oxide are produced from 100 g of calcium carbonate?
Q10. What is a stoichiometric coefficient? How does it help in calculating the amount of reactants and products?
Q11. Your mother follows a recipe that says: "2 cups flour + 1 cup sugar + 3 eggs → 1 cake." She wants to make 3 cakes. How does she calculate the ingredients needed? How is this exactly like stoichiometric calculations in chemistry?
Q12. Why is the actual yield of a chemical reaction usually less than the theoretical yield? Give two reasons.
Long Answer Questions
Q13. Explain the steps involved in stoichiometric calculations. Using the balanced equation:
2Na + Cl₂ → 2NaCl
Calculate:
(a) The mass of sodium chloride formed from 2.3 g of sodium
(b) The volume of chlorine gas at STP required to react with 2.3 g of sodium
(c) The number of moles of NaCl formed
(Atomic masses: Na = 23 u, Cl = 35.5 u)
Q14. Describe how to solve stoichiometric problems involving mass-mass, mass-volume, and volume-volume relationships. Illustrate with the combustion of methane:
CH₄ + 2O₂ → CO₂ + 2H₂O
Calculate:
(a) The mass of CO₂ produced from 16 g of CH₄
(b) The volume of O₂ required at STP to burn 16 g of CH₄
(c) The volume of CO₂ produced at STP
(Atomic masses: C = 12 u, H = 1 u, O = 16 u)
Q15. A student performs an experiment to prepare calcium carbonate by reacting calcium chloride with sodium carbonate:
CaCl₂ + Na₂CO₃ → CaCO₃ + 2NaCl
The student uses 11.1 g of CaCl₂ and 10.6 g of Na₂CO₃.
(a) Write the balanced equation and identify the stoichiometric coefficients.
(b) Calculate the theoretical yield of CaCO₃.
(c) If the student actually obtains 8.5 g of CaCO₃, calculate the percentage yield.
(d) Suggest two reasons why the actual yield might be less than the theoretical yield.
(Atomic masses: Ca = 40 u, Cl = 35.5 u, Na = 23 u, C = 12 u, O = 16 u)
Numerical / Application-Based Problems
Q16. Aluminium reacts with oxygen according to the equation:
4Al + 3O₂ → 2Al₂O₃
(a) Calculate the mass of aluminium oxide formed from 27 g of aluminium.
(b) Calculate the volume of oxygen at STP required to react completely with 27 g of aluminium.
(c) If 40.5 g of aluminium is used with excess oxygen, how many moles of Al₂O₃ are formed?
(Atomic masses: Al = 27 u, O = 16 u)
Q17. In the Haber process for manufacturing ammonia:
N₂ + 3H₂ → 2NH₃
A factory uses 280 kg of nitrogen gas per day.
(a) Calculate the mass of hydrogen required per day for complete reaction.
(b) Calculate the mass of ammonia produced per day.
(c) If the factory operates at 85% efficiency, what is the actual mass of ammonia produced?
(Atomic masses: N = 14 u, H = 1 u)
Q18. A chemist mixes 20 g of zinc with excess dilute sulphuric acid:
Zn + H₂SO₄ → ZnSO₄ + H₂
(a) Calculate the theoretical mass of zinc sulphate produced.
(b) Calculate the volume of hydrogen gas evolved at STP.
(c) If the reaction produces only 85% of the theoretical yield of ZnSO₄, calculate the actual mass obtained.
(d) The hydrogen gas is collected over water. If the total pressure is 1 atm and the vapour pressure of water at room temperature is 0.03 atm, what is the partial pressure of hydrogen?
(Atomic masses: Zn = 65 u, S = 32 u, O = 16 u, H = 1 u)