Test Session Chapter 4 Stoichiometry (1st Year Chemistry)

Q1. Multiple Choice Questions

10 Marks

Choose the correct option for each of the following questions. Each question carries 1 mark.

1. A solution contains 10.0 g of an unknown solute in 250 cm³ of solution. If the molar concentration of the solution is 0.20 mol dm^-3, what is the molar mass of the solute?

A 50 g mol^-1

B 100 g mol^-1

C 200 g mol^-1

D 400 g mol^-1

2. What is the number of atoms in 1 mole of any element?

A 3.01 × 10²³

B 6.02 × 10²³

C 1.00 × 10²⁰

D Depends on the element

3. To get equal number of atoms, we must use:

A Equal grams of each element

B Equal moles of each element

C Equal volume of each element

D Equal protons of each atom

4. Which of the following statements is true?

A 1 mole of CO₂ occupies 22.4 dm³ at STP

B 1 mole of any gas occupies 22.4 dm³ at STP

C 6.02 × 10²³ atoms of He occupy 22.4 g at STP

D All gases have the same mass at STP

5. What is the SI unit of density?

A mol/L

B g/dm³

C g/mol

D Kg·mol^-1

6. Why do heavier gases have greater density at STP?

A Because they are liquids

B Because they have higher molar masses

C Because they have higher volume

D Because they are lighter

7. If the molar mass of a gas increases, what happens to its density at STP?

A Increases

B Remains constant

C Decreases

D Doubles

8. Which formula is used to calculate percentage yield?

A Theoretical Yield / Actual Yield × 100

B Actual Yield / Theoretical Yield × 100

C Actual Yield × 100

D (Actual + Theoretical) / 2 × 100

9. What does a high percentage yield indicate?

A A failed reaction

B Reversible reaction

C Poor conditions

D High reaction efficiency

10. In a reaction, if theoretical yield is 10g and actual yield is 8g, what is the percentage yield?

A 125%

B 20%

C 80%

D 10%

Q2. Short Answer Questions

15 Marks

Write down short answers to the following questions.

9 g of potassium and 56 g of iron have equal number of atoms in them. Justify.
Do you think that 1 mole of H₂ and 1 mole of NH₄ at 0 °C and 1 atm will have Avogadro’s number of particles?
What are the factors which are mostly responsible for the low yield of the products in chemical reactions?
The given mass of KClO₄ is 24.5 g. Calculate its number of moles. (Quick Check 4.1)
How many molecules are present in 1.75 g of H₂O₂? (Quick Check 4.1)
Juglone is a dye produced from the husks of black walnuts. The formula for juglone is C₁₀H₆O₅.
(a) Calculate the molar mass of juglone.
(b) Calculate number of moles in 0.87 g of a sample of juglone extracted from black walnut husks. (Sample Problem 4.5)
Calculate the molar mass of a gas which has density of 1.34 g/dm³ at STP.
Calculate the mass of Al needed to react completely with 32.0 g of iron (III) oxide according to the equation given below:
2Al_(s) + Fe₂O_3(s) → Al₂O_3(s) + 2Fe_(s)
(Sample Problem 4.12)
What is stoichiometry?
Calculate the number of moles present in 20 g of NaOH.
What is the mass of 1 mole of Na atoms?
How many molecules are there in 18.0 g of water?
Do 1 mole of glucose and 1 mole of water contain equal number of molecules? Explain.
State Avogadro’s law in terms of gas volumes.
Calculate the volume occupied by 3 moles of oxygen gas at STP. (Quick Check 4.3)

Q3. Detailed Answer Questions

10 Marks

Write detailed answers to the following questions. (Answer any 2)

1. Differentiate actual and theoretical yields. Why is the theoretical yield always greater than actual yield?

2. A solution of sodium hydroxide (NaOH) is prepared by dissolving 2.00 g of solid sodium hydroxide in water to make a final volume of 250 cm³.
(a) Determine the molar mass of sodium hydroxide.
(b) Calculate the number of moles of sodium hydroxide used.
(c) Calculate the concentration of the sodium hydroxide solution in mol dm⁻³.
(d) If more water is added to the above solution to raise the volume of solution to 500 cm³, what would be the concentration now? (Numerical Problem)

3. Calculate volume of ammonia that can be produced by the reaction of 100 dm³ of hydrogen with excess of nitrogen at STP? The balanced chemical equation for the reaction is:

N_2(g) + 3H_2(g) → 2NH_3(g)

(Sample Problem 4.13)

Chemistry Examination

Chapter 4: Stoichiometry

MCQ Section Score