Q: What is the percent yield if the theoretical yield of CO2 is 10.0 g and the actual yield is 7.5 g?

$$\dfrac{7.5}{10.0} \times 100\% = 75\%$$

Q: What is the mass percent of nitrogen in NO2? (Atomic masses: N = 14.01, O = 16.00)

$$\dfrac{14.01}{46.01} \times 100\% = 30.45\%$$

Q: Which of the following is the correct formula for calculating mass percent?

$$\dfrac{\text{mass of element in 1 mol of compound}}{\text{mass of 1 mol of compound}} \times 100\%$$

Question 1

Which of the following best describes the difference between an empirical formula and a molecular formula?

Accepted Answer

The empirical formula shows the simplest whole-number ratio of atoms in a compound, while the molecular formula shows the actual number of atoms of each element in a molecule.

Question 2

A compound is found to contain 57.47% sodium, 40.01% oxygen, and 2.52% hydrogen by mass. What is the empirical formula of this compound? (Atomic masses: Na = 22.99, O = 16.00, H = 1.01)

Accepted Answer

$$\mathrm{Na_2OH}$$

Question 3

Which step is NOT part of the process for determining an empirical formula from percent composition?

Accepted Answer

Divide each mole value by the smallest mole value to get whole numbers.

Question 4

Ibuprofen has a molar mass of 206.3 g/mol and a percent composition of 75.70% C, 8.80% H, and 15.50% O. If its empirical formula is $$\mathrm{C$$_{13}$$H_{18}O_2$}$$, what is the n-factor used to determine the molecular formula?

Accepted Answer

$$n = \dfrac{206.3}{206.3}$$

Question 5

A 4.30 g sample of a compound containing only C, H, and O produces 8.59 g CO2 and 3.52 g H2O upon combustion. If the molar mass is 176.22 g/mol, what is the molecular formula of the compound?

Accepted Answer

$$\mathrm{C_8H_8O_4}$$

Question 6

In a combustion analysis, what is the first step after measuring the mass of CO2 and H2O produced?

Accepted Answer

Convert the grams of CO2 to grams of carbon.

Question 7

Given the following data from a combustion apparatus: Mass of CO2 absorber before combustion = 75.30 g, after combustion = 78.15 g; Mass of H2O absorber before combustion = 49.14 g, after combustion = 50.11 g. What is the mass of CO2 produced?

Accepted Answer

$$2.85\ \mathrm{g}$$

Question 8

Which of the following is the correct balanced equation for the combustion of ethanol ($$\mathrm{C_2H_6O}) in $$air?

Accepted Answer

$$\mathrm{C_2H_6O + 3\ O_2$ \rightarrow 2\ CO_2$ + 3\ H_2O}$$

Question 9

How many moles of hydrazine ($$\mathrm{N_2H_4}) $$are formed when 25.7 g of ammonia reacts with excess nitrogen gas? (Molar mass of NH3 = 17.03 g/mol)

Accepted Answer

$$1.13\ \mathrm{mol}$$

Question 10

A reaction between FeTiO3, Cl2, and C produces TiCl4. If 18.0 g FeTiO3, 30.0 g Cl2, and 40.0 g C are reacted, what is the limiting reagent?

Accepted Answer

FeTiO3

Question 11

What is the percent yield if the theoretical yield of CO2 is 10.0 g and the actual yield is 7.5 g?

Accepted Answer

$$\dfrac{7.5}{10.0} 	imes 100\% = 75\%$$

Question 12

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

Accepted Answer

The reactant that is completely consumed and determines the maximum amount of product formed.

Question 13

What is the mass percent of nitrogen in NO2? (Atomic masses: N = 14.01, O = 16.00)

Accepted Answer

$$\dfrac{14.01}{46.01} 	imes 100\% = 30.45\%$$

Question 14

Which of the following is a functional group that contains a carbonyl group?

Accepted Answer

Aldehyde

Question 15

A chemist isolates 10.0 g of NH3 from a reaction with a 79.3% yield. What was the theoretical yield?

Accepted Answer

$$\dfrac{10.0}{0.793} = 12.6\ \mathrm{g}$$

Question 16

Which of the following is the correct formula for calculating mass percent?

Accepted Answer

$$\dfrac{	ext{mass of element in 1 mol of compound}}{	ext{mass of 1 mol of compound}} 	imes 100\%$$

Chapter 4 Chemical Reactions and Chemical Quantities: Empirical & Molecular Formulas, Combustion Analysis, Stoichiometry, and Functional Groups

Study Guide - Practice Questions

Study Guide - Flashcards