Q: If you have $$6.52 \times 10$$^{23}$$ molecules of $$\mathrm{H}_2\mathrm{O}$$, how many moles of $$\mathrm{H}_2\mathrm{O}$$ do you have?

$$1.08$$ moles$$\ (\text{using}\ \frac{6.52 \times 10$$^{23}$$}{6.022 \times 10$$^{23}$$})$$

Question 1

Which of the following best describes the concept of stoichiometry in chemistry?

Accepted Answer

It deals with the numerical relationship between compounds in a balanced chemical equation.

Question 2

Given the balanced equation $$2 \mathrm{H}_2 (g) + 1 \mathrm{O}_2 (g) \rightarrow 2 \mathrm{H}_2\mathrm{O} (g)$$, how many moles of water are produced from 4 moles of hydrogen gas?

Accepted Answer

4 moles of hydrogen produce 4 moles of water, according to the 2:2 ratio in the equation.

Question 3

In the reaction $$4 \mathrm{Cr} (s) + 3 \mathrm{O}_2 (g) \rightarrow 2 \mathrm{Cr}_2\mathrm{O}_3 (s)$$, how many moles of $$\mathrm{Cr}_2\mathrm{O}_3$$ are produced from 8 moles of chromium?

Accepted Answer

4 moles

Question 4

If you start with 12.3 g of $$\mathrm{H}_2 in $$the reaction $$2 \mathrm{H}_2 (g) + 1 \mathrm{O}_2 (g) \rightarrow 2 \mathrm{H}_2\mathrm{O} (g)$$, what is the first step in determining the mass of water produced?

Accepted Answer

Convert grams of $$\mathrm{H}_2 to $$moles of $$\mathrm{H}_2.$$

Question 5

A student reacts 5.0 g of $$\mathrm{KClO}_3$$ with excess $$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$$ according to the equation $$6 \mathrm{KClO}_3 + \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 \rightarrow 6 \mathrm{KCl} + 6 \mathrm{CO}_2 + 6 \mathrm{H}_2\mathrm{O}. $$What is the limiting reactant?

Accepted Answer

$$\mathrm{KClO}_3$$

Question 6

In a stoichiometry problem, after converting grams of the given substance to moles, what is the next step?

Accepted Answer

Use the mole ratio from the balanced equation to find moles of the unknown.

Question 7

If the density of ethanol ($$\mathrm{CH}_3\mathrm{CH}_2\mathrm{OH}) is$$ $$0.789 \mathrm{g/mL}$$, how many milliliters are needed to produce $$4.0 \mathrm{g} of$$ $$\mathrm{H}_2\mathrm{O} in $$the reaction $$\mathrm{CH}_3\mathrm{CH}_2\mathrm{OH} + 3 \mathrm{O}_2 \rightarrow 3 \mathrm{H}_2\mathrm{O} + 2 \mathrm{CO}_2$$?

Accepted Answer

5.1 mL

Question 8

Which of the following is the correct mole ratio for $$\mathrm{O}_2 to$$ $$\mathrm{H}_2\mathrm{O} in $$the reaction $$2 \mathrm{H}_2 (g) + 1 \mathrm{O}_2 (g) \rightarrow 2 \mathrm{H}_2\mathrm{O} (g)$$?

Accepted Answer

1:2

Question 9

A chemical reaction produces $$8.34$$ mol of $$\mathrm{Cr}_2\mathrm{O}_3$$ from chromium and oxygen. If you started with $$34.8 g of$$ $$\mathrm{Cr}$$, what is the molar mass of $$\mathrm{Cr}$$ used in the calculation?

Accepted Answer

$$52.0 \mathrm{g/mol}$$

Question 10

In the reaction $$6 \mathrm{KClO}_3 + \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 ightarrow 6 \mathrm{KCl} + 6 \mathrm{CO}_2 + 6 \mathrm{H}_2\mathrm{O}$$, how many moles of $$\mathrm{CO}_2$$ are produced from $$2.3 	imes 10^2$ formula units of $$\mathrm{KClO}_3$$?

Accepted Answer

First convert formula units to moles, then use the 1:1 ratio to get moles of $$\mathrm{CO}_2.$$

Question 11

Which step in a stoichiometry problem involves using the coefficients from the balanced equation?

Accepted Answer

Mole to mole comparison

Question 12

A reaction produces $$12 \mathrm{CO}_2$$ and $$11 \mathrm{H}_2\mathrm{O}$$ from $$8 \mathrm{KClO}_3$$ and $$1 \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6. $$What is the total number of moles of products formed?

Accepted Answer

23 moles

Question 13

If you have $$6.52 	imes 10$$^{23}$$ molecules of $$\mathrm{H}_2\mathrm{O}$$, how many moles of $$\mathrm{H}_2\mathrm{O}$$ do you have?

Accepted Answer

$$1.08$$ moles$$\ (	ext{using}\ \frac{6.52 	imes 10$$^{23}$$}{6.022 	imes 10$$^{23}$$})$$

Question 14

Which of the following is NOT a necessary step in solving a stoichiometry problem?

Accepted Answer

Balancing the equation after calculations are complete

Question 15

A student needs to produce $$10.0 g of$$ $$\mathrm{H}_2\mathrm{O}$$ using $$\mathrm{H}_2$$ and $$\mathrm{O}_2. $$What is the minimum mass of $$\mathrm{O}_2$$ required?

Accepted Answer

First, convert $$10.0 g$$ $$\mathrm{H}_2\mathrm{O} to $$moles, then use the 1:2 ratio to find moles of $$\mathrm{O}_2$$, and finally convert to grams.

Stoichiometry and Mole-to-Mole Calculations in Chemical Reactions

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