Hard Grade 11 Chemistry Quiz: Basic Concepts | Set 8

Question 1

1. An unknown element $X$ has two naturally occurring isotopes. Isotope $A$ has a mass of $62.93$ u and Isotope $B$ has a mass of $64.93$ u. If the average atomic mass of $X$ is $63.55$ u, what is the percentage abundance of the lighter isotope?

A) $31.0\%$

B) $50.0\%$

C) $69.0\%$

D) $75.5\%$

Answer

Correct Answer: C

Solution: Let the abundance of Isotope $A$ ($62.93$ u) be $x$. Then abundance of Isotope $B$ ($64.93$ u) is $(1-x)$. $$63.55 = 62.93(x) + 64.93(1-x)$$ $$63.55 = 62.93x + 64.93 - 64.93x$$ $$63.55 - 64.93 = -2x$$ $$-1.38 = -2x \implies x = 0.69$$ Percentage abundance = $69.0\%$.

Question 2

2. A mixture of $2.0$ moles of $SO_2$ and $1.5$ moles of $O_2$ is reacted in a closed vessel to form $SO_3$. After the reaction reaches completion, how many moles of total gas molecules are present in the vessel?

A) $2.0$ moles

B) $2.5$ moles

C) $3.5$ moles

D) $1.5$ moles

Answer

Correct Answer: B

Reaction: $2SO_2 + O_2 \rightarrow 2SO_3$. Stoichiometric ratio of $SO_2 : O_2$ is $2:1$. Given: $2.0$ mol $SO_2$ and $1.5$ mol $O_2$. $SO_2$ is the limiting reagent (requires $1.0$ mol $O_2$). Moles of $O_2$ used = $1.0$ mol; Excess $O_2 = 1.5 - 1.0 = 0.5$ mol. Moles of $SO_3$ formed = $2.0$ mol. Total moles = Excess $O_2$ + Product $SO_3 = 0.5 + 2.0 = 2.5$ moles.

Question 3

3. An organic compound contains $40\%$ Carbon, $6.67\%$ Hydrogen, and the rest Oxygen. If the vapor density of the compound is $90$, determine the molecular formula.

A) $C_6H_{12}O_6$

B) $C_3H_6O_3$

C) $CH_2O$

D) $C_2H_4O_2$

Question 4

4. Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is $0.040$ (assume the density of water to be $1$ g/mL and the volume change on mixing is negligible).

A) $1.02$ M

B) $4.00$ M

C) $0.40$ M

D) $2.31$ M

Answer

Correct Answer: D

Mole fraction $X_{et} = \frac{n_{et}}{n_{et} + n_w} = 0.040$. Let total moles be $1$. $n_{et} = 0.04$ mol, $n_w = 0.96$ mol. Mass of water = $0.96 \times 18 = 17.28$ g. Volume of water (approx volume of solution) = $17.28$ mL = $0.01728$ L. Molarity = $\frac{0.04}{0.01728} \approx 2.31$ M.

Question 5

5. $10$ g of $CaCO_3$ is treated with $100$ mL of $0.5$ M $HCl$. What is the volume of $CO_2$ liberated at STP?

A) $0.56$ L

B) $1.12$ L

C) $2.24$ L

D) $22.4$ L

Answer

Correct Answer: A

Reaction: $CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2$. Moles $CaCO_3 = 10/100 = 0.1$ mol. Moles $HCl = 0.5 \times 0.1 = 0.05$ mol. From reaction, $2$ moles $HCl$ react with $1$ mole $CaCO_3$. $0.05$ mol $HCl$ will react with $0.025$ mol $CaCO_3$. $HCl$ is the limiting reagent. Moles of $CO_2$ formed = $1/2 \times \text{moles of } HCl = 0.025$ mol. Volume at STP = $0.025 \times 22.4 = 0.56$ L.

Question 6

6. The density of a $3.0$ M solution of $Na_2S_2O_3$ is $1.25$ g/mL. Calculate the molality of the solution. ($Na=23, S=32, O=16$)

A) $2.40$ m

B) $3.00$ m

C) $3.86$ m

D) $1.25$ m

Answer

Correct Answer: C

Molar mass of $Na_2S_2O_3 = 2(23) + 2(32) + 3(16) = 158$ g/mol. In $1$ L solution: Mass of solute = $3 \times 158 = 474$ g. Mass of solution = $1000 \text{ mL} \times 1.25 \text{ g/mL} = 1250$ g. Mass of solvent = $1250 - 474 = 776$ g = $0.776$ kg. Molality $m = \frac{\text{moles solute}}{\text{mass solvent in kg}} = \frac{3}{0.776} \approx 3.86$ m.

Question 7

7. Which of the following contains the same number of atoms as $12$ g of Magnesium? (At. mass $Mg=24, C=12, Ca=40$)

A) $12$ g of Carbon

B) $20$ g of Calcium

C) $24$ g of Magnesium

D) $1$ mole of Helium

Answer

Correct Answer: B

Moles of $Mg = 12/24 = 0.5$ mol. Number of atoms = $0.5 \times N_A$. A) $12/12 = 1.0$ mol. B) $20/40 = 0.5$ mol. (Matches) C) $24/24 = 1.0$ mol. D) $1.0$ mol.

Question 8

8. A sample of $H_2SO_4$ is $98\%$ by mass and has a density of $1.84$ g/mL. What volume of this acid is required to make $5.0$ L of $0.5$ M $H_2SO_4$?

A) $125$ mL

B) $136$ mL

C) $250$ mL

D) $500$ mL

Answer

Correct Answer: B

Molarity of stock $H_2SO_4 = \frac{\% \times d \times 10}{M.W.} = \frac{98 \times 1.84 \times 10}{98} = 18.4$ M. Using $M_1V_1 = M_2V_2$: $18.4 \times V_1 = 0.5 \times 5000$ mL $V_1 = 2500 / 18.4 \approx 135.87$ mL $\approx 136$ mL.

Question 9

9. If $6.3$ g of $NaHCO_3$ are added to $15.0$ g of $CH_3COOH$ solution, the residue is found to weigh $18.0$ g. What is the mass of $CO_2$ released in the reaction?

A) $4.2$ g

B) $1.5$ g

C) $2.1$ g

D) $3.3$ g

Answer

Correct Answer: D

According to the Law of Conservation of Mass: Total mass of reactants = Total mass of products Mass of ($NaHCO_3 + CH_3COOH$) = Mass of (Residue + $CO_2$) $6.3 + 15.0 = 18.0 + \text{mass of } CO_2$ $21.3 = 18.0 + x$ $x = 3.3$ g.

Question 10

10. A gaseous hydrocarbon gives upon combustion $0.72$ g of water and $3.08$ g of $CO_2$. The empirical formula of the hydrocarbon is:

A) $CH_4$

B) $C_2H_4$

C) $C_7H_8$

D) $C_3H_4$

Answer

Correct Answer: C

Moles of $CO_2 = 3.08 / 44 = 0.07$ mol. Moles of $C = 0.07$ mol. Moles of $H_2O = 0.72 / 18 = 0.04$ mol. Moles of $H = 2 \times 0.04 = 0.08$ mol. Ratio $C:H = 0.07 : 0.08 = 7 : 8$. Empirical Formula = $C_7H_8$.

Accepted Answer

Correct Answer: A

Carbon: $40/12 = 3.33$. Hydrogen: $6.67/1 = 6.67$. Oxygen: $(100-46.67)/16 = 3.33$. Ratio: $C:H:O = 1:2:1$. Empirical Formula = $CH_2O$. Empirical Formula Mass = $12 + 2 + 16 = 30$. Molecular Mass = $2 \times \text{Vapor Density} = 2 \times 90 = 180$. $n = 180/30 = 6$. Molecular Formula = $6 \times (CH_2O) = C_6H_{12}O_6$.

Grade 11 : Chemistry - Basic Concepts (Set 8) | Concept of Maths

Grade 11 : Chemistry - Basic Concepts (Set 8) | Concept of Maths

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4. Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is $0.040$ (assume the density of water to be $1$ g/mL and the volume change on mixing is negligible).

5. $10$ g of $CaCO_3$ is treated with $100$ mL of $0.5$ M $HCl$. What is the volume of $CO_2$ liberated at STP?

6. The density of a $3.0$ M solution of $Na_2S_2O_3$ is $1.25$ g/mL. Calculate the molality of the solution. ($Na=23, S=32, O=16$)

7. Which of the following contains the same number of atoms as $12$ g of Magnesium? (At. mass $Mg=24, C=12, Ca=40$)

8. A sample of $H_2SO_4$ is $98\%$ by mass and has a density of $1.84$ g/mL. What volume of this acid is required to make $5.0$ L of $0.5$ M $H_2SO_4$?

9. If $6.3$ g of $NaHCO_3$ are added to $15.0$ g of $CH_3COOH$ solution, the residue is found to weigh $18.0$ g. What is the mass of $CO_2$ released in the reaction?

10. A gaseous hydrocarbon gives upon combustion $0.72$ g of water and $3.08$ g of $CO_2$. The empirical formula of the hydrocarbon is:

Hard Grade 11 Chemistry Quiz: Basic Concepts | Set 8

1. An unknown element $X$ has two naturally occurring isotopes. Isotope $A$ has a mass of $62.93$ u and Isotope $B$ has a mass of $64.93$ u. If the average atomic mass of $X$ is $63.55$ u, what is the percentage abundance of the lighter isotope?

2. A mixture of $2.0$ moles of $SO_2$ and $1.5$ moles of $O_2$ is reacted in a closed vessel to form $SO_3$. After the reaction reaches completion, how many moles of total gas molecules are present in the vessel?

3. An organic compound contains $40\%$ Carbon, $6.67\%$ Hydrogen, and the rest Oxygen. If the vapor density of the compound is $90$, determine the molecular formula.

Grade 11 : Chemistry - Basic Concepts (Set 8) | Concept of Maths

Grade 11 : Chemistry - Basic Concepts (Set 8) | Concept of Maths

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4. Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is $0.040$ (assume the density of water to be $1$ g/mL and the volume change on mixing is negligible).

5. $10$ g of $CaCO_3$ is treated with $100$ mL of $0.5$ M $HCl$. What is the volume of $CO_2$ liberated at STP?

6. The density of a $3.0$ M solution of $Na_2S_2O_3$ is $1.25$ g/mL. Calculate the molality of the solution. ($Na=23, S=32, O=16$)

7. Which of the following contains the same number of atoms as $12$ g of Magnesium? (At. mass $Mg=24, C=12, Ca=40$)

8. A sample of $H_2SO_4$ is $98\%$ by mass and has a density of $1.84$ g/mL. What volume of this acid is required to make $5.0$ L of $0.5$ M $H_2SO_4$?

9. If $6.3$ g of $NaHCO_3$ are added to $15.0$ g of $CH_3COOH$ solution, the residue is found to weigh $18.0$ g. What is the mass of $CO_2$ released in the reaction?

10. A gaseous hydrocarbon gives upon combustion $0.72$ g of water and $3.08$ g of $CO_2$. The empirical formula of the hydrocarbon is: