Stoichiometry and Limiting Reactants Quiz

A chemical reaction between hydrogen gas and oxygen gas produces water. If you start with 4 moles of hydrogen and 3 moles of oxygen, which is the limiting reactant?

• Hydrogen

• Oxygen

• Water

• None of the above

Answer explanation

In the reaction 2H2 + O2 -> 2H2O, 4 moles of H2 require 2 moles of O2. Since we have 3 moles of O2, it is in excess. Therefore, oxygen is the limiting reactant.

Tags

NGSS.HS-PS1-7

Calculate the mass of water produced when 2 moles of hydrogen gas react completely with excess oxygen gas. (Molar mass of water = 18 g/mol)

• 18 g

• 36 g

• 54 g

• 72 g

Answer explanation

The reaction of 2 moles of H2 with excess O2 produces 2 moles of H2O. Using the molar mass of water (18 g/mol), the mass is 2 moles x 18 g/mol = 36 g. Thus, the correct answer is 36 g.

Tags

NGSS.HS-PS1-7

In a reaction between nitrogen gas and hydrogen gas to form ammonia, if 28 grams of nitrogen react with 6 grams of hydrogen, what is the percent yield if 30 grams of ammonia are produced? (Molar mass of ammonia = 17 g/mol)

• 50%

• 75%

• 88%

• 100%

Answer explanation

First, calculate the moles of nitrogen (28 g / 28 g/mol = 1 mol) and hydrogen (6 g / 2 g/mol = 3 mol). The limiting reactant is nitrogen. Theoretical yield of ammonia = 1 mol x 17 g/mol = 17 g. Percent yield = (30 g / 17 g) x 100 = 88%.

Tags

NGSS.HS-PS1-7

Plan an investigation to determine the limiting reactant in a reaction between sodium and chlorine gas to form sodium chloride. What would be the first step in your plan?

• Measure the mass of sodium

• Measure the mass of chlorine gas

• Calculate the moles of each reactant

• Mix the reactants and observe the reaction

Answer explanation

To determine the limiting reactant, you first need to know how much of each reactant is present. Calculating the moles of sodium and chlorine gas allows you to compare their ratios and identify which one will be consumed first in the reaction.

If 10 grams of calcium carbonate decompose to form calcium oxide and carbon dioxide, how many grams of calcium oxide are produced? (Molar mass of calcium carbonate = 100 g/mol, calcium oxide = 56 g/mol)

• 5.6 g

• 6.0 g

• 7.2 g

• 8.4 g

Answer explanation

The decomposition of calcium carbonate (CaCO3) produces calcium oxide (CaO) and carbon dioxide (CO2). From 10 g of CaCO3, using molar masses, we find 5.6 g of CaO is produced, confirming the correct answer is 5.6 g.

Tags

NGSS.HS-PS1-7

A reaction between aluminum and iron(III) oxide produces aluminum oxide and iron. If you start with 54 grams of aluminum and 160 grams of iron(III) oxide, which reactant is in excess?

• Aluminum

• Iron(III) oxide

• Aluminum oxide

• Iron

Answer explanation

To determine the excess reactant, calculate moles: Aluminum (54g) = 2 moles; Iron(III) oxide (160g) = 2 moles. The reaction ratio is 2:1, so 2 moles of Al can react with only 1 mole of Fe2O3. Thus, Aluminum is in excess.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

Determine the number of moles of carbon dioxide produced when 44 grams of propane (C₃H₈) combust completely. (Molar mass of propane = 44 g/mol)

• 1 mole

• 2 moles

• 3 moles

• 4 moles

Answer explanation

Combustion of propane (C₃H₈) produces 3 moles of CO₂ per mole of propane. Given 44 grams of propane (1 mole), the reaction yields 3 moles of CO₂. Thus, the correct answer is 3 moles.

In a lab experiment, you react 5 grams of magnesium with 10 grams of hydrochloric acid. How would you determine the limiting reactant?

• Measure the volume of hydrogen gas produced

• Calculate the moles of each reactant

• Measure the temperature change

• Observe the color change

Answer explanation

To determine the limiting reactant, calculate the moles of magnesium and hydrochloric acid. The reactant that produces fewer moles of product is the limiting reactant, as it will be consumed first in the reaction.

Tags

NGSS.HS-PS1-7

Calculate the percent yield if 20 grams of product are obtained from a reaction that theoretically produces 25 grams.

• 60%

• 70%

• 80%

• 90%

Answer explanation

Percent yield is calculated as (actual yield / theoretical yield) x 100. Here, (20 g / 25 g) x 100 = 80%. Therefore, the correct answer is 80%.

Tags

NGSS.HS-PS1-7

In a reaction between sulfur and oxygen to form sulfur dioxide, if 32 grams of sulfur react with 32 grams of oxygen, which is the limiting reactant?

• Sulfur

• Oxygen

• Sulfur dioxide

• None of the above

Answer explanation

In the reaction to form sulfur dioxide (SO2), the balanced equation is S + O2 -> SO2. 32 grams of sulfur (1 mol) requires 32 grams of oxygen (1 mol) to react completely. Since both reactants are present, but sulfur is in excess, sulfur is the limiting reactant.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5