Instructor's Manual: Mahaffey, Laboratory Experiments for General Organic and Biochemistry 1e 2027, 9781535883870; Experiment 1: Measurements in the
Laboratory
Instructor's Manual
MAHAFFEY, LABORATORY EXPERIMENTS FOR GENERAL ORGANIC AND BIOCHEMISTRY 1E 2027,
9781535883870; EXPERIMENT 1: MEASUREMENTS IN THE LABORATORY
EXPERIMENT 1
PRELAB EXERCISES: MEASUREMENT IN THE
LABORATORY
1. Define the difference between precision and accuracy. Give an example of each concept; the examples
should be different from the examples given in the Introduction.
Answer: Precision is the ability to reproduce data multiple times. Accuracy is the ability to find or
calculate the “true” value. An example of both is the calculation of monthly gas mileage over the
course of a year, and getting the correct calculated value (accuracy) each time (precision).
2. A student used a 500-mL graduated cylinder to measure the volume of water in a 1-cup measure. Three
trials of the measurement gave volumes of 240 mL, 242 mL, and 235 mL. What is the average of the three
measurements? Were the measurements precise? Were they accurate? You may wish to refer to conversion
factor tables to decide this. Justify your answers.
Answer: The average of the three trials is calculated as follows:
(240 mL + 242 mL + 235 mL)/ 3 = 239 mL.
Although each trial is not necessarily accurate, it is precise, as all three are reasonably close to the
average value (see Figure 1.3).
3. A student used a standard laboratory thermometer to measure the temperature of boiling water. On the lab
report sheet, the student recorded the boiling temperature as “94.” There are several problems with this
record. Describe two, and explain what the student should have written instead.
Answer: The student failed to record the temperature up to the tenths place for accuracy. The student
also failed to record the unit in degrees Celsius, as in 94⁰C. Standard laboratory thermometers decline
in accuracy over time. If the thermometer contains mercury, this is a possible hazard if it breaks open.
4. The mass of ten paper clips was found to be 10.135 g. What is the average mass of a paper clip in this
sample?
Answer: The average mass of a paper clip is calculated as follows:
10.135/10 = 1.0135 g
The numerical value of “1.0135” contains five (5) significant figures because the total mass of these
ten (10) paper clips was determined to be 10.135 g. The divisor “10” is used here to calculate the
average of the ten (10) paper clips; as such, it is an “exact number” and is considered to be a
significantly “infinite” number. Let’s combine these laws of measurements: We find that the numerical
dividend of 10.135 has five (5) significant figures and is divided by a divisor with an infinite number of
significant figures, and this results in a quotient of five significant figures (1.0135).
© 2027 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly 1
accessible website, in whole or in part.
,Instructor's Manual: Mahaffey, Laboratory Experiments for General Organic and Biochemistry 1e 2027, 9781535883870; Experiment 1: Measurements in the
Laboratory
5. In the laboratory, a student performed an experiment in which the final length of a piece of wire was a
significant measurement. In three separate experiments, the student found the length of the wire after the
experiment to be 23.50 mm, 25.0 mm, and 35 mm. Find the average of the three trials to the correct number
of significant figures, and decide if these measurements gave an accurate result.
Answer:
The average length of the piece of wire is calculated as follows:
(23.50 mm + 25.0 mm + 35 mm)/3 = 84 mm/3 = 28 mm
Refer students to significant figures rules for ADDITION, to see why there are 2 s.f.s for this response.
CHEMISTRY-N- MEDICINE
1. How many tablets of Xanax 0.25 mg should Mr. Jackson’s CNA give him?
a. 0.5 a tablet
b. 1.5 tablets
c. 2.0 tablets
d. None of the above
Answer: c.
2. How many tablets of digoxin 0.125 mg should the nurse administer to the patient?
a. 0.5 a tablet
b. 1.5 tablets
c. 2.0 tablets
d. None of the above
Answer: c.
© 2027 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly 2
accessible website, in whole or in part.
,Instructor's Manual: Mahaffey, Laboratory Experiments for General Organic and Biochemistry 1e 2027, 9781535883870; Experiment 2: density OF solids and liquids
Instructor's Manual
MAHAFFEY, LABORATORY EXPERIMENTS FOR GENERAL ORGANIC AND BIOCHEMISTRY 1E 2027,
9781535883870; EXPERIMENT 2: DENSITY OF SOLIDS AND LIQUIDS
EXPERIMENT 2
PRELAB EXERCISES: DENSITY OF SOLIDS AND LIQUIDS
1. A student measured the density of ethanol four times and obtained densities of 0.789, 0.810, 0.775, and
0.790.
a. What were the units for these measurements?
Answer: The most likely units of density were g/mL or g/cm3.
b. What was the average density obtained in the four trials?
Answer: The average density calculation is as follows:
(0.789 + 0.810 + 0.775 + 0.790)/4 = 0.7910 g/cm3
c. Were the results accurate and/or precise? Why or why not?
Answer: The density calculations for the four ethanol trials are -0.02, +0.02, -0.16, and +0.001 from
the average. Meaning the precision is all within range.
2. Chloroform (CHCl3) is a liquid that is not soluble in water. It has a density of 1.498 g/mL. A student
mixed a sample of chloroform with a sample of water and observed the result. Sketch what the
student saw, and identify all components of the drawing. For the container, draw a test tube.
Answer: The sample will have two distinct layers, water on top and chloroform on the bottom, due to
its higher density.
3. A 50.0-mL sample of ethylene glycol had a mass of 55.505 g. Find the density of ethylene glycol.
55.05 g
Answer: d = = 1.10 g / mL
50.0 mL
4. A sample of aluminum had a mass of 27.00 g. Since it was irregular in shape, the volume was obtained by
displacement of water. A 100-mL graduated cylinder of water was loaded with 50.00 mL of water, and the
aluminum piece was placed inside the cylinder. The water level rose to 60.05 mL. What was the density of
the aluminum block?
mass 27.00 g
Answer: d = = = 2.686 g / mL
V 2 - V 1 ( 60.05 - 50.00 mL )
PART D. EXERCISES
1. How precise is your data for the determination of the density of a liquid? Justify your answer.
Answer: Tip: Students may gauge the precision of their data by how closely the experimental data sets
agree with each other.
© 2027 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly 1
accessible website, in whole or in part.
, Instructor's Manual: Mahaffey, Laboratory Experiments for General Organic and Biochemistry 1e 2027, 9781535883870; Experiment 2: density OF solids and liquids
2. How precise is your data for the determination of the density of a solid? Justify your answer.
Answer: Tip: Students may gauge the precision of their data by how closely the expeirmental data sets
agree with each other.
3. Use the Internet to determine which naturally occurring element is the densest. Cite your source using APA
format. Which is it, and what is its density?
Answer: Osmium (elemental symbol: Os) has the higher density, at 22.59 g/cm3. Citations may vary,
4. Devise a flow chart for the determination of the density of a solid ball that floats on water. If your
experiment works, and you find that the volume of water displaced by adding the ball is 15.2 mL and the
mass of the ball is 12.1 mL, what is the density?
Answer: Student responses may vary.
5. Given that the average density of fat is about 0.9 g/cm3 and the average density of muscle is about 1.10
g/cm3, why might individuals with a higher-than-average fat composition find it easier to float than
individuals with higher-than-average muscle mass?
Answer: Given the density of fat is 0.9 g/cm3 and that of muscle is on average 1.10 g/cm3, we return
to the topic of “buoyancy” (the ability of a person or object to float on water). Therefore, fat floats and
muscle sinks when you consider that 0.9 g/cm3 (fat) is less than 1.00 g/cm3 (the density of water)
and 1.10 g/cm3 (muscle) is greater than 1.00 g/mL. The same idea may be applied to the floating
capabilities of the individuals discussed in this question: one with a higher-than-average body fat
percentage may float more so than someone with a higher-than-average muscle mass.
CHEMISTRY-N- MEDICINE
1. Darren Miller, a 57-year-old patient, received the results from his recent DEXA scan: T-score = -2.1.
Which of the following is the most likely diagnosis?
a. Healthy bones
b. Osteopenia
c. Osteoporosis
d. None of the above
Answer: b.
2. Keisha Miller, his 59-year-old wife, also received the results from her recent DEXA scan: T-score = -2.9.
What is the most likely diagnosis?
a. Healthy bones
b. Osteopenia
c. Osteoporosis
d. None of the above
Answer: c.
© 2027 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly 2
accessible website, in whole or in part.
Laboratory
Instructor's Manual
MAHAFFEY, LABORATORY EXPERIMENTS FOR GENERAL ORGANIC AND BIOCHEMISTRY 1E 2027,
9781535883870; EXPERIMENT 1: MEASUREMENTS IN THE LABORATORY
EXPERIMENT 1
PRELAB EXERCISES: MEASUREMENT IN THE
LABORATORY
1. Define the difference between precision and accuracy. Give an example of each concept; the examples
should be different from the examples given in the Introduction.
Answer: Precision is the ability to reproduce data multiple times. Accuracy is the ability to find or
calculate the “true” value. An example of both is the calculation of monthly gas mileage over the
course of a year, and getting the correct calculated value (accuracy) each time (precision).
2. A student used a 500-mL graduated cylinder to measure the volume of water in a 1-cup measure. Three
trials of the measurement gave volumes of 240 mL, 242 mL, and 235 mL. What is the average of the three
measurements? Were the measurements precise? Were they accurate? You may wish to refer to conversion
factor tables to decide this. Justify your answers.
Answer: The average of the three trials is calculated as follows:
(240 mL + 242 mL + 235 mL)/ 3 = 239 mL.
Although each trial is not necessarily accurate, it is precise, as all three are reasonably close to the
average value (see Figure 1.3).
3. A student used a standard laboratory thermometer to measure the temperature of boiling water. On the lab
report sheet, the student recorded the boiling temperature as “94.” There are several problems with this
record. Describe two, and explain what the student should have written instead.
Answer: The student failed to record the temperature up to the tenths place for accuracy. The student
also failed to record the unit in degrees Celsius, as in 94⁰C. Standard laboratory thermometers decline
in accuracy over time. If the thermometer contains mercury, this is a possible hazard if it breaks open.
4. The mass of ten paper clips was found to be 10.135 g. What is the average mass of a paper clip in this
sample?
Answer: The average mass of a paper clip is calculated as follows:
10.135/10 = 1.0135 g
The numerical value of “1.0135” contains five (5) significant figures because the total mass of these
ten (10) paper clips was determined to be 10.135 g. The divisor “10” is used here to calculate the
average of the ten (10) paper clips; as such, it is an “exact number” and is considered to be a
significantly “infinite” number. Let’s combine these laws of measurements: We find that the numerical
dividend of 10.135 has five (5) significant figures and is divided by a divisor with an infinite number of
significant figures, and this results in a quotient of five significant figures (1.0135).
© 2027 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly 1
accessible website, in whole or in part.
,Instructor's Manual: Mahaffey, Laboratory Experiments for General Organic and Biochemistry 1e 2027, 9781535883870; Experiment 1: Measurements in the
Laboratory
5. In the laboratory, a student performed an experiment in which the final length of a piece of wire was a
significant measurement. In three separate experiments, the student found the length of the wire after the
experiment to be 23.50 mm, 25.0 mm, and 35 mm. Find the average of the three trials to the correct number
of significant figures, and decide if these measurements gave an accurate result.
Answer:
The average length of the piece of wire is calculated as follows:
(23.50 mm + 25.0 mm + 35 mm)/3 = 84 mm/3 = 28 mm
Refer students to significant figures rules for ADDITION, to see why there are 2 s.f.s for this response.
CHEMISTRY-N- MEDICINE
1. How many tablets of Xanax 0.25 mg should Mr. Jackson’s CNA give him?
a. 0.5 a tablet
b. 1.5 tablets
c. 2.0 tablets
d. None of the above
Answer: c.
2. How many tablets of digoxin 0.125 mg should the nurse administer to the patient?
a. 0.5 a tablet
b. 1.5 tablets
c. 2.0 tablets
d. None of the above
Answer: c.
© 2027 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly 2
accessible website, in whole or in part.
,Instructor's Manual: Mahaffey, Laboratory Experiments for General Organic and Biochemistry 1e 2027, 9781535883870; Experiment 2: density OF solids and liquids
Instructor's Manual
MAHAFFEY, LABORATORY EXPERIMENTS FOR GENERAL ORGANIC AND BIOCHEMISTRY 1E 2027,
9781535883870; EXPERIMENT 2: DENSITY OF SOLIDS AND LIQUIDS
EXPERIMENT 2
PRELAB EXERCISES: DENSITY OF SOLIDS AND LIQUIDS
1. A student measured the density of ethanol four times and obtained densities of 0.789, 0.810, 0.775, and
0.790.
a. What were the units for these measurements?
Answer: The most likely units of density were g/mL or g/cm3.
b. What was the average density obtained in the four trials?
Answer: The average density calculation is as follows:
(0.789 + 0.810 + 0.775 + 0.790)/4 = 0.7910 g/cm3
c. Were the results accurate and/or precise? Why or why not?
Answer: The density calculations for the four ethanol trials are -0.02, +0.02, -0.16, and +0.001 from
the average. Meaning the precision is all within range.
2. Chloroform (CHCl3) is a liquid that is not soluble in water. It has a density of 1.498 g/mL. A student
mixed a sample of chloroform with a sample of water and observed the result. Sketch what the
student saw, and identify all components of the drawing. For the container, draw a test tube.
Answer: The sample will have two distinct layers, water on top and chloroform on the bottom, due to
its higher density.
3. A 50.0-mL sample of ethylene glycol had a mass of 55.505 g. Find the density of ethylene glycol.
55.05 g
Answer: d = = 1.10 g / mL
50.0 mL
4. A sample of aluminum had a mass of 27.00 g. Since it was irregular in shape, the volume was obtained by
displacement of water. A 100-mL graduated cylinder of water was loaded with 50.00 mL of water, and the
aluminum piece was placed inside the cylinder. The water level rose to 60.05 mL. What was the density of
the aluminum block?
mass 27.00 g
Answer: d = = = 2.686 g / mL
V 2 - V 1 ( 60.05 - 50.00 mL )
PART D. EXERCISES
1. How precise is your data for the determination of the density of a liquid? Justify your answer.
Answer: Tip: Students may gauge the precision of their data by how closely the experimental data sets
agree with each other.
© 2027 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly 1
accessible website, in whole or in part.
, Instructor's Manual: Mahaffey, Laboratory Experiments for General Organic and Biochemistry 1e 2027, 9781535883870; Experiment 2: density OF solids and liquids
2. How precise is your data for the determination of the density of a solid? Justify your answer.
Answer: Tip: Students may gauge the precision of their data by how closely the expeirmental data sets
agree with each other.
3. Use the Internet to determine which naturally occurring element is the densest. Cite your source using APA
format. Which is it, and what is its density?
Answer: Osmium (elemental symbol: Os) has the higher density, at 22.59 g/cm3. Citations may vary,
4. Devise a flow chart for the determination of the density of a solid ball that floats on water. If your
experiment works, and you find that the volume of water displaced by adding the ball is 15.2 mL and the
mass of the ball is 12.1 mL, what is the density?
Answer: Student responses may vary.
5. Given that the average density of fat is about 0.9 g/cm3 and the average density of muscle is about 1.10
g/cm3, why might individuals with a higher-than-average fat composition find it easier to float than
individuals with higher-than-average muscle mass?
Answer: Given the density of fat is 0.9 g/cm3 and that of muscle is on average 1.10 g/cm3, we return
to the topic of “buoyancy” (the ability of a person or object to float on water). Therefore, fat floats and
muscle sinks when you consider that 0.9 g/cm3 (fat) is less than 1.00 g/cm3 (the density of water)
and 1.10 g/cm3 (muscle) is greater than 1.00 g/mL. The same idea may be applied to the floating
capabilities of the individuals discussed in this question: one with a higher-than-average body fat
percentage may float more so than someone with a higher-than-average muscle mass.
CHEMISTRY-N- MEDICINE
1. Darren Miller, a 57-year-old patient, received the results from his recent DEXA scan: T-score = -2.1.
Which of the following is the most likely diagnosis?
a. Healthy bones
b. Osteopenia
c. Osteoporosis
d. None of the above
Answer: b.
2. Keisha Miller, his 59-year-old wife, also received the results from her recent DEXA scan: T-score = -2.9.
What is the most likely diagnosis?
a. Healthy bones
b. Osteopenia
c. Osteoporosis
d. None of the above
Answer: c.
© 2027 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly 2
accessible website, in whole or in part.
