Stoichiometry Trivia Test: MCQ Quiz!

1. Which reactant is the excess reactant?

Ammonia

Copper(II) oxide

In a chemical reaction, the excess reactant is the reactant that is present in a greater amount than required for the reaction to proceed to completion. In this case, ammonia is the excess reactant because it is mentioned first in the list of reactants. This implies that there is an excess amount of ammonia compared to copper(II) oxide, indicating that ammonia is present in a greater quantity than necessary for the reaction.

Explanation

In a chemical reaction, the excess reactant is the reactant that is present in a greater amount than required for the reaction to proceed to completion. In this case, ammonia is the excess reactant because it is mentioned first in the list of reactants. This implies that there is an excess amount of ammonia compared to copper(II) oxide, indicating that ammonia is present in a greater quantity than necessary for the reaction.

2. When copper(II) oxide is heated with hydrogen gas, water and copper metal is produced. What mass of copper can be obtained if 32.0g of copper(II) oxide is used?

24.3g

25.5g

27.6g

When copper(II) oxide is heated with hydrogen gas, a chemical reaction occurs and water and copper metal are produced. The balanced chemical equation for this reaction is: CuO + H2 → Cu + H2O. According to the equation, 1 mole of copper(II) oxide (CuO) reacts to produce 1 mole of copper (Cu). To find the mass of copper that can be obtained, we need to convert the mass of copper(II) oxide (32.0g) to moles using its molar mass (79.55g/mol), and then use the mole ratio from the balanced equation to find the mass of copper produced. The calculation gives us a mass of approximately 25.5g of copper.

Explanation

When copper(II) oxide is heated with hydrogen gas, a chemical reaction occurs and water and copper metal are produced. The balanced chemical equation for this reaction is: CuO + H2 → Cu + H2O. According to the equation, 1 mole of copper(II) oxide (CuO) reacts to produce 1 mole of copper (Cu). To find the mass of copper that can be obtained, we need to convert the mass of copper(II) oxide (32.0g) to moles using its molar mass (79.55g/mol), and then use the mole ratio from the balanced equation to find the mass of copper produced. The calculation gives us a mass of approximately 25.5g of copper.

3. If 40g of ammonia reacts with 80.0g copper (II) oxide, determine the limiting reactant. Use nitrogen gas as your unknown.

Ammonia

Copper(II) oxide

In order to determine the limiting reactant, we need to compare the amount of ammonia and copper (II) oxide used in the reaction. The molar mass of ammonia (NH3) is 17.03 g/mol, so 40g of ammonia is approximately 2.35 moles. The molar mass of copper (II) oxide (CuO) is 79.55 g/mol, so 80.0g of copper (II) oxide is approximately 1.00 mole. Since the molar ratio between ammonia and copper (II) oxide is 2:1, we can see that there are more moles of ammonia than copper (II) oxide. Therefore, copper (II) oxide is the limiting reactant in this reaction.

Explanation

In order to determine the limiting reactant, we need to compare the amount of ammonia and copper (II) oxide used in the reaction. The molar mass of ammonia (NH3) is 17.03 g/mol, so 40g of ammonia is approximately 2.35 moles. The molar mass of copper (II) oxide (CuO) is 79.55 g/mol, so 80.0g of copper (II) oxide is approximately 1.00 mole. Since the molar ratio between ammonia and copper (II) oxide is 2:1, we can see that there are more moles of ammonia than copper (II) oxide. Therefore, copper (II) oxide is the limiting reactant in this reaction.

4. Nitrogen monoxide reacts with oxygen gas to produce nitrogen dioxide. What are the coefficients that balance the equation?

2,1,2

1,2,1

2,1,1

The coefficients that balance the equation are 2, 1, 2. This means that 2 molecules of nitrogen monoxide react with 1 molecule of oxygen gas to produce 2 molecules of nitrogen dioxide. The balanced equation is 2NO + O2 -> 2NO2.

Explanation

The coefficients that balance the equation are 2, 1, 2. This means that 2 molecules of nitrogen monoxide react with 1 molecule of oxygen gas to produce 2 molecules of nitrogen dioxide. The balanced equation is 2NO + O2 -> 2NO2.

5. Ammonia, , and copper (II) oxide react to form solid copper, water and nitrogen gas. What are the coefficients for the balanced chemical equations.

2,2,2,1,1

1,2,1,2,1

2,3,3,3,1

The balanced chemical equation for the reaction between ammonia, copper (II) oxide, and copper is 2NH3 + 3CuO -> 3Cu + 3H2O + N2. This equation shows that 2 moles of ammonia react with 3 moles of copper (II) oxide to produce 3 moles of copper, 3 moles of water, and 1 mole of nitrogen gas. Therefore, the coefficients for the balanced chemical equation are 2, 3, 3, 3, 1.

Explanation

The balanced chemical equation for the reaction between ammonia, copper (II) oxide, and copper is 2NH3 + 3CuO -> 3Cu + 3H2O + N2. This equation shows that 2 moles of ammonia react with 3 moles of copper (II) oxide to produce 3 moles of copper, 3 moles of water, and 1 mole of nitrogen gas. Therefore, the coefficients for the balanced chemical equation are 2, 3, 3, 3, 1.

6. What is the percent yield of hydrogen gas if 3.80g of hydrogen is collected in the lab?

94%

88%

96%

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Explanation

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7. Determine the mass of nitrogen gas produced in the reaction.

9.4 g

14.0g

28.0 g

The mass of nitrogen gas produced in the reaction is 9.4 g.

Explanation

The mass of nitrogen gas produced in the reaction is 9.4 g.

8. What is the theoretical yield of hydrogen gas if 36.0 g of water decomposes to produce hydrogen gas and oxygen gas?

2.02 g H2

1.01 g H2

4.04 g H2

The theoretical yield of hydrogen gas can be calculated using the stoichiometry of the reaction. The balanced equation for the decomposition of water is 2H2O -> 2H2 + O2. From the equation, we can see that for every 2 moles of water, we get 2 moles of hydrogen gas. The molar mass of water is 18.02 g/mol, so 36.0 g of water is equal to 2 moles. Therefore, the theoretical yield of hydrogen gas is also 2 moles, which is equal to 4.04 g H2.

Explanation

The theoretical yield of hydrogen gas can be calculated using the stoichiometry of the reaction. The balanced equation for the decomposition of water is 2H2O -> 2H2 + O2. From the equation, we can see that for every 2 moles of water, we get 2 moles of hydrogen gas. The molar mass of water is 18.02 g/mol, so 36.0 g of water is equal to 2 moles. Therefore, the theoretical yield of hydrogen gas is also 2 moles, which is equal to 4.04 g H2.

9. How much of the excess reactant remains after the reaction? **Ammonia is the excess reactant, meaning it will not be completely used up in a reaction. In other words, you will not be using all 40g of ammonia given. In order to find out how much is left over after the reaction, do a mass-mass problem. 80g CuO is the given and grams of ammonia is the unknown. This answer is how much ammonia is used up. Now, figure out how much is leftover!

19.8 g

32.4 g

28.6 g

Ammonia is the excess reactant, meaning it will not be completely used up in the reaction. To determine how much is left over, a mass-mass problem can be used. The given mass of copper(II) oxide (CuO) is 80g, and the mass of ammonia is the unknown. The answer, 28.6g, represents the amount of ammonia that is used up in the reaction, while the remaining amount is the excess reactant that remains.

Explanation

Ammonia is the excess reactant, meaning it will not be completely used up in the reaction. To determine how much is left over, a mass-mass problem can be used. The given mass of copper(II) oxide (CuO) is 80g, and the mass of ammonia is the unknown. The answer, 28.6g, represents the amount of ammonia that is used up in the reaction, while the remaining amount is the excess reactant that remains.