Q: A sample contains 3.00 g of carbon and 8.00 g of oxygen. What is the percent composition by mass of carbon in the sample?

$$\frac{3.00}{3.00 + 8.00} \times 100 = 27.3\%$$

Q: A naturally occurring element consists of two isotopes: 70.0% isotope A (mass = 10.0 amu) and 30.0% isotope B (mass = 11.0 amu). What is the atomic weight of the element?

$$0.700 \times 10.0 + 0.300 \times 11.0 = 10.3$$ amu

Q: How many molecules are present in 0.250 mol of water?

$$0.250 \times 6.022 \times 10$$^{23}$$ = 1.51 \times 10$$^{23}$$ molecules

Q: A 5.00 g sample of a compound contains 2.00 g of nitrogen and 3.00 g of oxygen. What is the percent by mass of oxygen?

$$\frac{3.00}{5.00} \times 100 = 60.0\%$$

Question 1

Which of the following best illustrates the Law of Multiple Proportions?

Accepted Answer

Two compounds, NO and NO$$_2$$, contain nitrogen and oxygen in mass ratios of 14:16 and 14:32, respectively.

Question 2

A sample contains 3.00 g of carbon and 8.00 g of oxygen. What is the percent composition by mass of carbon in the sample?

Accepted Answer

$$\frac{3.00}{3.00 + 8.00} 	imes 100 = 27.3\%$$

Question 3

Which statement about subatomic particles is correct?

Accepted Answer

Protons and neutrons have approximately the same mass, while electrons are much less massive.

Question 4

A naturally occurring element consists of two isotopes: 70.0% isotope A (mass = 10.0 amu) and 30.0% isotope B (mass = 11.0 amu). What is the atomic weight of the element?

Accepted Answer

$$0.700 	imes 10.0 + 0.300 	imes 11.0 = 10.3$$ amu

Question 5

Which element is located in Group 2, Period 3 of the periodic table?

Accepted Answer

Magnesium (Mg)

Question 6

How many moles are in 25.0 g of glucose ($$\mathrm{C_6H_{12}O_6$}$$)? (Molar mass = 180.0 g/mol)

Accepted Answer

$$\frac{25.0\ \mathrm{g}}{180.0\ \mathrm{g/mol}} = 0.139\ \mathrm{mol}$$

Question 7

A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

Accepted Answer

CH$$_2O$$

Question 8

Which of the following best describes the Law of Conservation of Mass?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 9

How many significant figures are in the measurement 0.004560?

Accepted Answer

4

Question 10

A student needs to prepare 250.0 mL of 0.100 M NaCl solution from a 1.00 M NaCl stock solution. What volume of stock solution is required?

Accepted Answer

$$M_1V_1 = M_2V_2$$ 
$$V_1$$ = \frac{M_2V_2}{$$M_1$$} = \frac{0.100 	imes 250.0}{1.00} = 25.0\ \mathrm{mL}$$

Question 11

Which of the following is a molecular compound?

Accepted Answer

CO$$_2$$

Question 12

Balance the following equation: 
$$\mathrm{C_2H_6} + \mathrm{O_2$} \rightarrow \mathrm{CO_2$} + \mathrm{H_2O}$$

Accepted Answer

$$2\ \mathrm{C_2H_6} + 7\ \mathrm{O_2$} \rightarrow 4\ \mathrm{CO_2$} + 6\ \mathrm{H_2O}$$

Question 13

How many molecules are present in 0.250 mol of water?

Accepted Answer

$$0.250 	imes 6.022 	imes 10$$^{23}$$ = 1.51 	imes 10$$^{23}$$ molecules

Question 14

A reaction requires 0.500 mol of H$$_2$$ and excess O$$_2. $$How many grams of H$$_2$$ are needed? (Molar mass H$$_2 = 2.02 g/$$mol)

Accepted Answer

$$0.500 	imes 2.02 = 1.01 g$$

Question 15

A 5.00 g sample of a compound contains 2.00 g of nitrogen and 3.00 g of oxygen. What is the percent by mass of oxygen?

Accepted Answer

$$\frac{3.00}{5.00} 	imes 100 = 60.0\%$$

Question 16

Which of the following conversions is set up correctly to convert 25.0 inches to centimeters? (1 inch = 2.54 cm)

Accepted Answer

$$25.0\ \mathrm{in} 	imes \frac{2.54\ \mathrm{cm}}{1\ \mathrm{in}}$$

Question 17

A solution is prepared by diluting 10.0 mL of 6.00 M HCl to a final volume of 100.0 mL. What is the final concentration?

Accepted Answer

$$M_1V_1 = M_2V_2$$ 
$$M_2$$ = \frac{M_1V_1}{$$V_2$$} = \frac{6.00 	imes 10.0}{100.0} = 0.600\ \mathrm{M}$$

Question 18

Which of the following best describes a period on the periodic table?

Accepted Answer

A horizontal row of elements

Question 19

A sample of a compound contains 0.100 mol of C, 0.200 mol of H, and 0.100 mol of O. What is the empirical formula?

Accepted Answer

CH$$_2O$$

General Chemistry Exam 1 Study Guide: Fundamental Concepts and Calculations

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