Class 10 Mole Concept and Stoichiometry Mock Test (ICSE)

Topics in Mole Concept and Stoichiometry

• Gay-Lussac's law of combining volumes
• Avogadro's law
• Mole and molar volume
• Empirical and molecular formula
• Calculations from chemical equations

Mole Concept and Stoichiometry practice questions with answers

1. Q1Multiple choice·1 mark
   What is the mass of $5.6\text{ dm}^3$ of carbon dioxide ($\text{CO}_2$) gas at STP?

   1. (a)$44\text{ g}$
   2. (b)$22\text{ g}$
   3. (c)$11\text{ g}$
   4. (d)$5.5\text{ g}$
   Show answer and step marks

   1. Correct option: (c) $11\text{ g}$. Moles = $\frac{5.6\text{ dm}^3}{22.4\text{ dm}^3\text{ mol}^{-1}} = 0.25\text{ mol}$, Mass = $0.25\text{ mol} \times 44\text{ g mol}^{-1} = 11\text{ g}$.+1

   Answer: (c)
2. Q2Multiple choice·1 mark
   An organic compound has an empirical formula $\text{CHO}$ and its vapour density is $29$. What is its molecular formula?

   1. (a)$\text{CHO}$
   2. (b)$\text{C}_2\text{H}_2\text{O}_2$
   3. (c)$\text{C}_2\text{H}_4\text{O}_2$
   4. (d)$\text{C}_3\text{H}_3\text{O}_3$
   Show answer and step marks

   1. Correct option: (b) $\text{C}_2\text{H}_2\text{O}_2$. Molecular mass = $2 \times \text{vapour density} = 58$. Empirical formula mass = $29$. $n = 58 / 29 = 2$. Molecular formula = $(\text{CHO})_2 = \text{C}_2\text{H}_2\text{O}_2$.+1

   Answer: (b)
3. Q3Multiple choice·1 mark
   According to Gay-Lussac's law of combining volumes, gases react in volumes which bear a simple whole number ratio to one another and to the volume of the gaseous products, provided all volumes are measured at:

   1. (a)Standard temperature and $1\text{ atm}$ pressure
   2. (b)Same temperature and pressure
   3. (c)Same temperature and different pressures
   4. (d)Different temperatures and same pressure
   Show answer and step marks

   1. Correct option: (b) Same temperature and pressure.+1

   Answer: (b)
4. Q4Multiple choice·1 mark
   What volume of oxygen gas at STP is required to burn completely $4\text{ g}$ of methane gas? (Reaction: $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$)

   1. (a)$11.2\text{ dm}^3$
   2. (b)$22.4\text{ dm}^3$
   3. (c)$44.8\text{ dm}^3$
   4. (d)$5.6\text{ dm}^3$
   Show answer and step marks

   1. Correct option: (a) $11.2\text{ dm}^3$. Moles of $\text{CH}_4 = 4 / 16 = 0.25\text{ mol}$. Moles of $\text{O}_2$ required = $0.25 \times 2 = 0.5\text{ mol}$. Volume at STP = $0.5 \times 22.4 = 11.2\text{ dm}^3$.+1

   Answer: (a)
5. Q5Short answer·2 marks
   State Avogadro's Law. Using this law, deduce the atomicity of hydrogen, given that hydrogen reacts with chlorine to form hydrogen chloride gas in the volume ratio $1 : 1 : 2$ under similar conditions of temperature and pressure.
   Show answer and step marks

   1. State Avogadro's law: Equal volumes of all gases under similar conditions of temperature and pressure contain the same number of molecules.+1
   2. Apply Avogadro's law to the reaction: $1\text{ molecule of hydrogen} + 1\text{ molecule of chlorine} \rightarrow 2\text{ molecules of hydrogen chloride}$.+0.5
   3. Since $1\text{ molecule of hydrogen}$ gives $2\text{ molecules of hydrogen chloride}$, each containing $1$ atom of hydrogen, $1\text{ molecule of hydrogen}$ must contain $2$ atoms. Hence, atomicity is $2$.+0.5

   Answer: Avogadro's law: equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules. 1 molecule of hydrogen gives 2 molecules of HCl, each with 1 hydrogen atom, so the atomicity of hydrogen is 2.
6. Q6Short answer·2 marks
   State Avogadro's law. If $100\text{ mL}$ of nitrogen gas contains $x$ molecules, how many molecules will be present in $300\text{ mL}$ of carbon dioxide gas under the same conditions of temperature and pressure?
   Show answer and step marks

   1. State Avogadro's law: Equal volumes of all gases under similar conditions of temperature and pressure contain equal numbers of molecules.+1
   2. Apply the law: Since $300\text{ mL}$ is three times $100\text{ mL}$, it contains $3 \times x = 3x$ molecules.+1

   Answer: Avogadro's law: equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules. 300 mL is three times 100 mL, so it contains $3x$ molecules.

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