Q: A student is preparing a solution by dissolving 10.0 g of NaCl in enough water to make 250 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

$$\frac{10.0\ \text{g}}{58.44\ \text{g/mol}} = 0.171\ \text{mol}$$; $$M = \frac{0.171\ \text{mol}}{0.250\ \text{L}} = 0.684\ \text{M}$$

Q: A solution is prepared by mixing 25.0 mL of ethanol (density = 0.789 g/mL) with 75.0 mL of water. What is the mass percent of ethanol in the solution?

Mass of ethanol = $$25.0\ \text{mL} \times 0.789\ \text{g/mL} = 19.725\ \text{g}$$; Mass of water = $$75.0\ \text{mL} \times 1.00\ \text{g/mL} = 75.0\ \text{g}$$; Total mass = $$19.725 + 75.0 = 94.725\ \text{g}$$; Mass percent ethanol = $$\frac{19.725}{94.725} \times 100\% = 20.8\%$$

Q: A student titrates 25.0 mL of HCl with 0.100 M NaOH. If it takes 30.0 mL of NaOH to reach the endpoint, what is the molarity of the HCl solution?

$$M_1V_1 = M_2V_2$$; $$M_1$$ \times 25.0\ \text{mL} = 0.100\ \text{M} \times 30.0\ \text{mL}$$; M_1$ = \frac{0.100 \times 30.0}{25.0} = 0.120\ \text{M}$$

Q: A student measures the mass of a flask as 250.0 g and then adds 50.0 mL of water. The total mass is now 300.0 g. What is the density of the water added?

Density = $$\frac{300.0\ \text{g} - 250.0\ \text{g}}{50.0\ \text{mL}} = \frac{50.0\ \text{g}}{50.0\ \text{mL}} = 1.00\ \text{g/mL}$$

Q: Which of the following is the correct formula for calculating the number of moles of solute in a solution?

$$\text{moles} = \text{molarity} \times \text{volume (in liters)}$$

Question 1

Which of the following is the best reason for wearing safety goggles at all times in the laboratory?

Accepted Answer

To protect your eyes from accidental chemical splashes and flying debris.

Question 2

A student is preparing a solution by dissolving 10.0 g of NaCl in enough water to make 250 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

Accepted Answer

$$\frac{10.0\ 	ext{g}}{58.44\ 	ext{g/mol}} = 0.171\ 	ext{mol}$$; $$M = \frac{0.171\ 	ext{mol}}{0.250\ 	ext{L}} = 0.684\ 	ext{M}$$

Question 3

Which laboratory safety rule is most directly violated if a student works alone in the lab without supervision?

Accepted Answer

UNSUPERVISED WORK is strictly forbidden.

Question 4

A solution is prepared by mixing 25.0 mL of ethanol (density = 0.789 g/mL) with 75.0 mL of water. What is the mass percent of ethanol in the solution?

Accepted Answer

Mass of ethanol = $$25.0\ 	ext{mL} 	imes 0.789\ 	ext{g/mL} = 19.725\ 	ext{g}$$; Mass of water = $$75.0\ 	ext{mL} 	imes 1.00\ 	ext{g/mL} = 75.0\ 	ext{g}$$; Total mass = $$19.725 + 75.0 = 94.725\ 	ext{g}$$; Mass percent ethanol = $$\frac{19.725}{94.725} 	imes 100\% = 20.8\%$$

Question 5

Which of the following is NOT a recommended practice for maintaining academic integrity in the laboratory?

Accepted Answer

Copying another student's lab report and submitting it as your own.

Question 6

A student titrates 25.0 mL of HCl with 0.100 M NaOH. If it takes 30.0 mL of NaOH to reach the endpoint, what is the molarity of the HCl solution?

Accepted Answer

$$M_1V_1 = M_2V_2$$; $$M_1$$ 	imes 25.0\ 	ext{mL} = 0.100\ 	ext{M} 	imes 30.0\ 	ext{mL}$$; M_1$ = \frac{0.100 	imes 30.0}{25.0} = 0.120\ 	ext{M}$$

Question 7

Which of the following statements about Thin Layer Chromatography (TLC) is correct?

Accepted Answer

TLC separates compounds based on their differing affinities for the stationary and mobile phases.

Question 8

Which metric prefix represents a factor of $$1/1000$$?

Accepted Answer

milli-

Question 9

A student measures the mass of a flask as 250.0 g and then adds 50.0 mL of water. The total mass is now 300.0 g. What is the density of the water added?

Accepted Answer

Density = $$\frac{300.0\ 	ext{g} - 250.0\ 	ext{g}}{50.0\ 	ext{mL}} = \frac{50.0\ 	ext{g}}{50.0\ 	ext{mL}} = 1.00\ 	ext{g/mL}$$

Question 10

Which of the following is a structural feature that distinguishes a carbohydrate from an alcohol?

Accepted Answer

Carbohydrates contain multiple hydroxyl groups and a carbonyl group (aldehyde or ketone), while alcohols contain only a hydroxyl group.

Question 11

During the synthesis of aspirin, which functional group is introduced to salicylic acid?

Accepted Answer

An ester group ($$-COO-)$$

Question 12

Which of the following is the correct formula for calculating the number of moles of solute in a solution?

Accepted Answer

$$	ext{moles} = 	ext{molarity} 	imes 	ext{volume (in liters)}$$

Question 13

A student is asked to determine the specific gravity of a liquid. Which of the following is the correct definition?

Accepted Answer

Specific gravity is the ratio of the density of a substance to the density of water.

Question 14

Which of the following is a common real-world application of neutralization reactions?

Accepted Answer

Using antacids to relieve heartburn by neutralizing excess stomach acid.

Question 15

Which of the following statements about academic integrity is FALSE?

Accepted Answer

It is acceptable to copy another student's report if you change a few words.

Question 16

A student is using a 50 mL graduated cylinder with an uncertainty of $$\pm 0.2 mL. If $$the student records a volume of 37.6 mL, what is the correct way to report the measurement?

Accepted Answer

$$37.6\ 	ext{mL} \pm 0.2\ 	ext{mL}$$

Question 17

Which of the following is a correct safety procedure if a chemical spill occurs in the laboratory?

Accepted Answer

Report the accident to your laboratory instructor immediately.

Question 18

Which of the following best describes the role of the laboratory notebook?

Accepted Answer

It provides a permanent, accurate record of your work in the laboratory.

CHEM 109L Laboratory Safety, Integrity, and Measurement Techniques – Study Notes

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