Question 1

1. A sample of 10.0 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 g. What is the value of x? (Atomic masses: Ba = 137, Cl = 35.5, H = 1, O = 16)

A) 1B) 3C) 2D) 4

Answer

✓ Correct Answer: Option C

Explanation: Mass of water lost = 10.0 - 8.525 = 1.475g. Moles of $BaCl_2 = \frac{8.525}{137 + (2 \times 35.5)} = \frac{8.525}{208} \approx 0.041 mol$. Moles of $H_2O = \frac{1.475}{18} \approx 0.082 mol$. 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)$If 170 g ofNH_3and 320 g ofO_2are reacted, and the actual yield ofNOis 120 g, what is the percentage yield? (Molar masses:NH_3=17, O_2=32, NO=30$)

60%

Question 3

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

A) 125.5 mLB) 62.4 mLC) 150.0 mLD) 136.0 mL

Answer

✓ Correct Answer: Option D

Explanation: Molarity of stock $H_2SO_4 = \frac{% \times d \times 10}{M_w} = \frac{98 \times 1.84 \times 10}{98} = 18.4m$. Using $M_1V_1 = M_2V_2$: $18.4 \times V_1 = 0.5 \times 5000$ $V_1 = \frac{2500}{18.4} \approx 135.87 mL \approx 136.0 mL$. Correct Answer: 136.0 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_2B) CH_2OC) C_3H_6O_3D) C_2H_2O_4

Answer

✓ Correct Answer: Option A

Explanation: 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 = $2 \times Vapor Density = 2 \times 30 = 60$. 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 M solution of NaCl with a density of 1.25 g/mL? (Molar mass of NaCl = 58.5 g/mol)

A) 2.40 mB) 3.00 mC) 2.79 mD) 3.25 m

Answer

✓ Correct Answer: Option C

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

Question 6

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

A) NaCl and NaBrB) CO and CO_2C) H_2O and D_2OD) MgO and Mg(OH)_2

Answer

✓ Correct Answer: Option B

Explanation: 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 m is x and in $4.50 \times 10^3m$ is y, then x+y is:

A) 4B) 5C) 7D) 6

Answer

✓ Correct Answer: Option D

Explanation: 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 moles of $H_2$ and 1.0 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 molesB) 3.0 molesC) 1.5 molesD) 2.5 moles

Answer

✓ Correct Answer: Option A

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

Question 9

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

A) 500B) 1000C) 1500D) 2000

Answer

✓ Correct Answer: Option B

Explanation: Atomic mass of $X = Mass of 1 atom \times N_A = 6.644 \times 10^{-23} \times 6.022 \times 10^{23} \approx 40 g/mol$. Number of gram-atoms (moles) = $\frac{Total mass}{Atomic mass} = \frac{40000g}{40 g/mol} = 1000$. 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) 12B) 24C) 36D) 48

Answer

✓ Correct Answer: Option A

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

Accepted Answer

✓ Correct Answer: Option B

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

Grade 11 Chemistry Quiz - Basic Concepts Set 9

1. A sample of 10.0 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 g. What is the value of x? (Atomic masses: Ba = 137, Cl = 35.5, H = 1, O = 16)

2. In a process for producing nitric acid, ammonia is oxidized: $$4NH_3(g) + 5O_2(g) \rightarrow 4NO(g) + 6H_2O(g)$If 170 g ofNH_3and 320 g ofO_2are reacted, and the actual yield ofNOis 120 g, what is the percentage yield? (Molar masses:NH_3=17, O_2=32, NO=30$)

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

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?

5. What is the molality of a 3.0 M solution of NaCl with a density of 1.25 g/mL? (Molar mass of NaCl = 58.5 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 m is x and in $4.50 \times 10^3m$ is y, then x+y is:

8. A mixture of 2.0 moles of $H_2$ and 1.0 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 $6.644 \times 10^{-23}g$. Calculate the number of gram-atoms in 40 kg of this element.

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