Grade 11 Chemistry Quiz - Basic Concepts Set 9 | Concept of Maths

Question 1

1. A sample of $10.0\text{ g}$ of a hydrate of barium chloride ($BaCl_2 \cdot xH_2O$) is heated until all the water of crystallization is removed. The residue of anhydrous barium chloride weighs $8.525\text{ g}$. What is the value of $x$? (Atomic masses: $Ba = 137, Cl = 35.5, H = 1, O = 16$)

A) 1

B) 3

C) 2

D) 4

Answer

Correct Answer: C

Mass of water lost = $10.0 - 8.525 = 1.475\text{ g}$. Moles of $BaCl_2 = \frac{8.525}{137 + (2 \times 35.5)} = \frac{8.525}{208} \approx 0.041\text{ mol}$. Moles of $H_2O = \frac{1.475}{18} \approx 0.082\text{ mol}$. Ratio $x = \frac{n(H_2O)}{n(BaCl_2)} = \frac{0.082}{0.041} = 2$. Correct Answer: 2

Question 2

2. In a process for producing nitric acid, ammonia is oxidized: $$4NH_3(g) + 5O_2(g) \rightarrow 4NO(g) + 6H_2O(g)$$ If $170\text{ g}$ of $NH_3$ and $320\text{ g}$ of $O_2$ are reacted, and the actual yield of $NO$ is $120\text{ g}$, what is the percentage yield? (Molar masses: $NH_3=17, O_2=32, NO=30$)

A) 60%

B) 50%

C) 75%

D) 40%

Answer

Correct Answer: B

Moles of $NH_3 = \frac{170}{17} = 10\text{ mol}$. Moles of $O_2 = \frac{320}{32} = 10\text{ mol}$. Stoichiometric ratio is $4:5$. For $10\text{ mol } NH_3$, $12.5\text{ mol } O_2$ is needed. Thus, $O_2$ is the limiting reagent. Theoretical yield of $NO = \frac{4}{5} \times 10 = 8\text{ mol}$. Mass of $NO = 8 \times 30 = 240\text{ g}$. % Yield = $\frac{120}{240} \times 100 = 50\%$. Correct Answer: 50%

Question 3

3. A solution of $H_2SO_4$ has a density of $1.84\text{ g/mL}$ and is $98\%$ by mass. Calculate the volume of this acid required to prepare $5.0\text{ L}$ of $0.5\text{ M } H_2SO_4$.

A) 125.5 mL

Question 4

4. An organic compound contains $40\%$ carbon, $6.67\%$ hydrogen, and the rest oxygen. If the vapor density of the compound is 30, what is its molecular formula?

A) C_2H_4O_2

B) CH_2O

C) C_3H_6O_3

D) C_2H_2O_4

Answer

Correct Answer: A

Carbon: $40/12 = 3.33$. Hydrogen: $6.67/1 = 6.67$. Oxygen: $(100-46.67)/16 = 3.33$. Empirical ratio: $1:2:1 \rightarrow CH_2O$. Empirical mass = $12 + 2 + 16 = 30$. Molecular mass = $2 \times \text{Vapor Density} = 2 \times 30 = 60$. $n = 60/30 = 2$. Molecular formula = $(CH_2O)_2 = C_2H_4O_2$. Correct Answer: $C_2H_4O_2$

Question 5

5. What is the molality of a $3.0\text{ M}$ solution of $NaCl$ with a density of $1.25\text{ g/mL}$? (Molar mass of $NaCl = 58.5\text{ g/mol}$)

A) 2.40 m

B) 3.00 m

C) 2.79 m

D) 3.25 m

Answer

Correct Answer: C

Assume $1\text{ L}$ solution. Mass of solution = $1000 \times 1.25 = 1250\text{ g}$. Mass of $NaCl = 3 \times 58.5 = 175.5\text{ g}$. Mass of solvent = $1250 - 175.5 = 1074.5\text{ g} = 1.0745\text{ kg}$. Molality $m = \frac{\text{moles solute}}{\text{kg solvent}} = \frac{3}{1.0745} \approx 2.79\text{ m}$. Correct Answer: 2.79 m

Question 6

6. The law of multiple proportions is illustrated by which pair of compounds?

A) NaCl and NaBr

B) CO and CO_2

C) H_2O and D_2O

D) MgO and Mg(OH)_2

Answer

Correct Answer: B

The law of multiple proportions states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers. $CO$ and $CO_2$ contain the same two elements (C and O) in different ratios ($1:1$ and $1:2$ by atoms). Correct Answer: $CO$ and $CO_2$

Question 7

7. If the number of significant figures in the measurement $0.00450\text{ m}$ is $x$ and in $4.50 \times 10^3\text{ m}$ is $y$, then $x+y$ is:

A) 4

B) 5

C) 7

D) 6

Answer

Correct Answer: D

In $0.00450$, the leading zeros are not significant, but the trailing zero is. Significant figures ($x$) = 3 (4, 5, 0). In $4.50 \times 10^3$, all digits in the coefficient are significant. Significant figures ($y$) = 3 (4, 5, 0). $x + y = 3 + 3 = 6$. Correct Answer: 6

Question 8

8. A mixture of $2.0\text{ moles}$ of $H_2$ and $1.0\text{ mole}$ of $O_2$ is reacted to form water. If the reaction goes to completion, what is the total number of moles of substance present in the container (assuming water is in gaseous state)?

A) 2.0 moles

B) 3.0 moles

C) 1.5 moles

D) 2.5 moles

Answer

Correct Answer: A

Reaction: $2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$. Initial: $2\text{ mol } H_2$ and $1\text{ mol } O_2$. Since they are in a $2:1$ ratio, both are completely consumed. Product: $2\text{ moles of } H_2O(g)$. Total moles = $2.0\text{ moles}$. Correct Answer: 2.0 moles

Question 9

9. The mass of one atom of an element $X$ is $6.644 \times 10^{-23}\text{ g}$. Calculate the number of gram-atoms in $40\text{ kg}$ of this element.

A) 500

B) 1000

C) 1500

D) 2000

Answer

Correct Answer: B

Atomic mass of $X = \text{Mass of 1 atom} \times N_A = 6.644 \times 10^{-23} \times 6.022 \times 10^{23} \approx 40\text{ g/mol}$. Number of gram-atoms (moles) = $\frac{\text{Total mass}}{\text{Atomic mass}} = \frac{40000\text{ g}}{40\text{ g/mol}} = 1000$. Correct Answer: 1000

Question 10

10. An oxide of a metal contains $40\%$ oxygen by mass. What is the equivalent mass of the metal?

A) 12

B) 24

C) 36

D) 48

Answer

Correct Answer: A

Equivalent mass of metal = $\frac{\text{Mass of metal}}{\text{Mass of oxygen}} \times 8$. Mass of oxygen = $40\text{ g}$. Mass of metal = $100 - 40 = 60\text{ g}$. Equivalent mass = $\frac{60}{40} \times 8 = 1.5 \times 8 = 12$. Correct Answer: 12

Accepted Answer

Correct Answer: D

Molarity of stock $H_2SO_4 = \frac{\% \times d \times 10}{M_w} = \frac{98 \times 1.84 \times 10}{98} = 18.4\text{ M}$. Using $M_1V_1 = M_2V_2$: $18.4 \times V_1 = 0.5 \times 5000$ $V_1 = \frac{2500}{18.4} \approx 135.87\text{ mL} \approx 136.0\text{ mL}$. Correct Answer: 136.0 mL

Grade 11 : Chemistry - Basic Concepts (Set 9) | Concept of Maths

Grade 11 : Chemistry - Basic Concepts (Set 9) | Concept of Maths

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4. An organic compound contains $40\%$ carbon, $6.67\%$ hydrogen, and the rest oxygen. If the vapor density of the compound is 30, what is its molecular formula?

5. What is the molality of a $3.0\text{ M}$ solution of $NaCl$ with a density of $1.25\text{ g/mL}$? (Molar mass of $NaCl = 58.5\text{ g/mol}$)

6. The law of multiple proportions is illustrated by which pair of compounds?

7. If the number of significant figures in the measurement $0.00450\text{ m}$ is $x$ and in $4.50 \times 10^3\text{ m}$ is $y$, then $x+y$ is:

8. A mixture of $2.0\text{ moles}$ of $H_2$ and $1.0\text{ mole}$ of $O_2$ is reacted to form water. If the reaction goes to completion, what is the total number of moles of substance present in the container (assuming water is in gaseous state)?

9. The mass of one atom of an element $X$ is $6.644 \times 10^{-23}\text{ g}$. Calculate the number of gram-atoms in $40\text{ kg}$ of this element.

10. An oxide of a metal contains $40\%$ oxygen by mass. What is the equivalent mass of the metal?

Grade 11 Chemistry Quiz - Basic Concepts Set 9 | Concept of Maths

1. A sample of $10.0\text{ g}$ of a hydrate of barium chloride ($BaCl_2 \cdot xH_2O$) is heated until all the water of crystallization is removed. The residue of anhydrous barium chloride weighs $8.525\text{ g}$. What is the value of $x$? (Atomic masses: $Ba = 137, Cl = 35.5, H = 1, O = 16$)

3. A solution of $H_2SO_4$ has a density of $1.84\text{ g/mL}$ and is $98\%$ by mass. Calculate the volume of this acid required to prepare $5.0\text{ L}$ of $0.5\text{ M } H_2SO_4$.

Grade 11 : Chemistry - Basic Concepts (Set 9) | Concept of Maths

Grade 11 : Chemistry - Basic Concepts (Set 9) | Concept of Maths

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4. An organic compound contains $40\%$ carbon, $6.67\%$ hydrogen, and the rest oxygen. If the vapor density of the compound is 30, what is its molecular formula?

5. What is the molality of a $3.0\text{ M}$ solution of $NaCl$ with a density of $1.25\text{ g/mL}$? (Molar mass of $NaCl = 58.5\text{ g/mol}$)

6. The law of multiple proportions is illustrated by which pair of compounds?

7. If the number of significant figures in the measurement $0.00450\text{ m}$ is $x$ and in $4.50 \times 10^3\text{ m}$ is $y$, then $x+y$ is:

8. A mixture of $2.0\text{ moles}$ of $H_2$ and $1.0\text{ mole}$ of $O_2$ is reacted to form water. If the reaction goes to completion, what is the total number of moles of substance present in the container (assuming water is in gaseous state)?

9. The mass of one atom of an element $X$ is $6.644 \times 10^{-23}\text{ g}$. Calculate the number of gram-atoms in $40\text{ kg}$ of this element.

10. An oxide of a metal contains $40\%$ oxygen by mass. What is the equivalent mass of the metal?