Q: What is the correct formula to determine the multiple $$x$$ for a molecular formula from an empirical formula?

$$x = \dfrac{\text{molar mass}}{\text{empirical molar mass}}$$

Q: How do you calculate the mass of excess reactant remaining after a reaction?

$$\text{excess mass} = \text{given mass} - \text{mass (reacted)}$$

Question 1

A compound has an empirical formula of CH and a molar mass of 78 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_6$$

Question 2

Given a compound containing 1.52 g of nitrogen and 3.47 g of oxygen, with a molar mass of 92 g/mol, what is its molecular formula?

Accepted Answer

$$\mathrm{N}_2\mathrm{O}_4$$

Question 3

Which of the following best describes the limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed first, limiting the amount of product formed

Question 4

In the reaction $$2\mathrm{Al} + \mathrm{Fe}_2\mathrm{O}_3 \rightarrow \mathrm{Al}_2\mathrm{O}_3 + 2\mathrm{Fe}$$, if 124 g of Al and 601 g of $$\mathrm{Fe}_2\mathrm{O}_3$$ are reacted, what is the mass of $$\mathrm{Al}_2\mathrm{O}_3$$ formed?

Accepted Answer

$$234\ \mathrm{g}$$

Question 5

What is the correct formula to determine the multiple $$x$$ for a molecular formula from an empirical formula?

Accepted Answer

$$x = \dfrac{	ext{molar mass}}{	ext{empirical molar mass}}$$

Question 6

If 1.00 g of glucose ($$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6) is $$completely combusted, how many grams of water are produced? (Molar mass of glucose = 180.0 g/mol)

Accepted Answer

$$0.600\ \mathrm{g}$$

Question 7

Which step is NOT part of the limiting reactant calculation method?

Accepted Answer

Use the excess reactant in all calculations

Question 8

How do you calculate the mass of excess reactant remaining after a reaction?

Accepted Answer

$$	ext{excess mass} = 	ext{given mass} - 	ext{mass (reacted)}$$

Question 9

A student mixes 10.0 g of hydrogen ($$\mathrm{H}_2) $$with 80.0 g of oxygen ($$\mathrm{O}_2) to $$produce water. Which is the limiting reactant?

Accepted Answer

$$\mathrm{H}_2$$

Question 10

What is the percent yield if the theoretical yield of a reaction is 50 g and the actual yield is 40 g?

Accepted Answer

$$80\%$$

Question 11

In a reaction, the actual yield is always:

Accepted Answer

Less than or equal to the theoretical yield

Question 12

Which of the following is true about stoichiometric calculations?

Accepted Answer

They use coefficients from the balanced equation to relate amounts of substances

Question 13

If you start with 124 g of Al and 601 g of $$\mathrm{Fe}_2\mathrm{O}_3 in $$the reaction $$2\mathrm{Al} + \mathrm{Fe}_2\mathrm{O}_3 \rightarrow \mathrm{Al}_2\mathrm{O}_3 + 2\mathrm{Fe}$$, which reactant is in excess?

Accepted Answer

$$\mathrm{Fe}_2\mathrm{O}_3$$

Question 14

A reaction has a theoretical yield of 100 g, but only 60 g of product is obtained. What is the percent yield?

Accepted Answer

$$60\%$$

Question 15

Which of the following is the correct sequence for a stoichiometric calculation involving grams of reactant and grams of product?

Accepted Answer

Grams of reactant $$\rightarrow$$ moles of reactant $$\rightarrow$$ moles of product $$\rightarrow$$ grams of product

Question 16

In the reaction $$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2 \rightarrow 6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O}$$, how many moles of water are produced from 1 mole of glucose?

Accepted Answer

6 moles

Question 17

If a reaction has two reactants, A and B, and you calculate that A produces 5 moles of product while B produces 3 moles, which is the limiting reactant?

Accepted Answer

B

Question 18

Which of the following is NOT a reason for a percent yield less than 100%?

Accepted Answer

All reactants are pure and react completely

Question 19

In a balanced chemical equation $$aA + bB \rightarrow cC + dD$$, what do the coefficients $$a$$, $$b$$, $$c$$, and $$d$$ represent?

Accepted Answer

The number of moles of each substance involved in the reaction

Chemical Reactions and Reaction Stoichiometry: Molecular Formulas, Limiting Reactants, and Stoichiometric Calculations

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