Chemistry 151
Lab 2: Measurements & Chemical Changes
Last Updated: Dec. 2013
Introduction
This lab will serve as an introduction to some of the basic techniques and skills you’ll be using in this course (and
most of your future science courses). It will also introduce you to the idea of measuring and recording in the correct
number of significant figures, which were discussed in Chapter 1.
In lecture, you’re usually presented with data measured or recorded by someone else (usually in the form of a word
problem) and you have to determine how many significant figures are present in each value. During lab, however,
you are the one making the measurements, so it’s your responsibility to record them in the correct number of
significant figures. The number of significant figures will be determined by the instrument you use to make a given
measurement. For example, a balance that can measure out to milligrams (0.001 g) would allow you to record
masses with more accuracy —and therefore more significant figures—than one that only goes out to the first
decimal place (0.1 g).
We will also explore the concept of physical and chemical changes, which was also discussed in Chapter 1. You’re
not expected to know the details of any chemical reactions you might observe during this week’s lab. That’ll happen
later in the semester.
Procedure
PART I: Accuracy & Precision
A. Pipettes vs. Graduated Cylinders
1. Use a volumetric pipette (the good ones, not the smaller, disposable ones) to measure 10 mL of water. The fill line
will be a small line above the fat section of the pipette. You may use a rubber bulb or plastic pump (see me if you’re
unsure how to use either).
2. Transfer the water to a 25 mL graduated cylinder.
3. Measure a second 10 mL of water with your volumetric pipette and transfer it to the graduated cylinder, adding it
to your initial measurement (giving you a total of 20 mL).
4. Repeat steps 1-3 twice, for a total of three trials (empty your graduated cylinder between each trial).
5. Repeat steps 1-4 using 20 mL water and a 100 mL graduated cylinder.
B. Graduated Cylinders vs. Beakers
1. Use a 25 or 50 mL graduated cylinder to transfer 50 mL to a 250 mL beaker.
2. Transfer another 50 mL (giving you a total of 100 mL)
3. Repeat step 2 again (giving you a total of 150 mL and ) then once more (for a total of 200 mL)
4. Repeat steps 1-3 twice, for a total of three trials (empty your beaker between each trial).
5. Repeat steps 1-3, this time using a 100 mL graduated cylinder to transfer a total of 400 mL to a 600 mL beaker.
PART II: Combining Volumes
A. Combining liquids
1. Using a volumetric pipette, measure 20 mL of water and transfer it to a 50 mL graduated cylinder.
2. Measure 20 mL of isopropanol (2-propanol) with a volumetric pipette and add it to the graduated cylinder. Gently
swirl to mix.
3. Repeat steps 1 and 2 for a second trial.
B. Combining a solid with a liquids
1. Measure approximately 5 g of sodium chloride and add it to beaker (100-250 mL).
2. Measure 20 mL of water using a graduated cylinder and add it to the beaker.
3. Mix well and transfer the solution to the graduated cylinder.
4. Repeat steps 1-3.
PART III: Chemical & Physical Changes
A. Reactions with sodium hydroxide
1. Add a small amount of copper (II) sulfate to a small test tube (enough to cover the very bottom of the tube should
do). Dissolve the solid by adding enough water to fill the tube ½ to ¾ full). Gently shake to mix
2. Repeat step 1 in a second test tube, this time using baking soda (sodium bicarbonate).
3. Add a few drops of 6 M sodium hydroxide to each test tube (you’ll learn what the “6 M” means later in the
semester).
B. Reactions with zinc
1. Repeat steps 1 and 2 of Part A
2. Add a small amount of zinc powder to each test tube, and let stand for 5-10 minutes to see if a reaction occurs.
C. Reactions with acetic acid
1. Repeat steps 1 and 2 of Part A
2. Add a few drops of vinegar to each test tube.
Wastes Disposal.
Water and solutions from Parts I and II can go down the drain with running water. Waste from Part III will be
disposed of in the waste hood.
Name: _____________________________
Section: ________
Data
PART I: Accuracy & Precision
A. Pipettes vs. Graduated Cylinders
10 mL pipette:
Accuracy of instrument:
(listed near top)
±________
Range of actual measurement
(based on accuracy)
_________ to _________
Volume measured, ml
(in correct significant figures)
_________
Trial 1
Trial 2
Trial 3
Volume according to graduated cylinder, mL
(first 10 mL)
_______
_______
_______
Volume after second 10 mL addition, mL
_______
_______
_______
20 mL pipette:
Accuracy of instrument:
(listed near top)
±________
Range of actual measurement
(based on accuracy)
_________ to _________
Volume measured, ml
(in correct significant figures)
_________
Trial 1
Trial 2
Trial 3
Volume according to graduated cylinder, mL
(first 20 mL)
_______
_______
_______
Volume after second 20 mL addition, mL
_______
_______
_______
B. Graduated Cylinders vs. Beakers
50 mL graduated cylinder/250 mL beaker:
Volume
(graduated cylinder)
Volume (according to beaker)
Trial 1
Trial 2
Trial 3
50 mL
_______
_______
_______
100 mL
_______
_______
_______
150 mL
_______
_______
_______
200 mL
_______
_______
_______
100 mL graduated cylinder/600 mL beaker:
Volume
(graduated cylinder)
Volume (according to beaker)
Trial 1
Trial 2
Trial 3
100 mL
_______
_______
_______
200 mL
_______
_______
_______
300 mL
_______
_______
_______
400 mL
_______
_______
_______
What is the accuracy range given for each beaker (if none is given, assume ±5%)?
250 mL: __________
600 mL: __________
What is the range of the actual measurement in each case?
250 mL: __________ to __________
600 mL: __________ to __________
PART II: Combining Volumes
A. Pipettes vs. Graduated Cylinders
Trial 1
Trial 2
Volume of water added, mL
(according to pipette)
_______
_______
Volume of isopropanol added, mL
(according to pipette)
_______
_______
_______
_______
Trial 1
Trial 2
Mass of sodium chloride, g
_______
_______
Volume of sodium chloride, mL
(d = 2.17 g/mL)
_______
_______
Volume of water, mL
_______
_______
Volume of solution, mL
_______
_______
Total volume, mL
(according to graduated cylinder)
B. Combining a solid with a liquids
PART III: Chemical & Physical Changes
A. Reactions with sodium hydroxide
Observations:
B. Reactions with zinc
Obersvations:
C. Reactions with acetic acid
Observations:
Name: _____________________________
Section: ________
Post-lab questions
1.Rank the accuracy of the three instruments you used to measure volumes, from least accurate to most.
2. Given your results, explain what people mean when they say that volumes aren’t “additive.”
3. In Part III, when you dissolved the copper (II) sulfate and sodium bicarbonate in water, were they undergoing a
physical or chemical change? Explain.
4. Which compound from Part III appeared to undergo a chemical change when combined with each of the
following? In each case, explain your answer.
a) sodium hydroxide?
b) zinc?
c) acetic acid?
Name: _____________________________
Section: ________
Pre-lab questions
1. Define the following
a) chemical change
b) physical change
c) accuracy
d) precision
2. How many significant figures are in each of the following measurements (assuming none are exact)?
a) 5.010 grams
_____ b) 10.0 mL _____ c) 75 ft _____
3. Record the volume shown below in the correct number of significant figures? _______ mL
4. Watch the following video on using volumetric pipettes: http://youtu.be/qorl6rKLmRs
a) How do you get rid of any liquid in the tip that could potential contaminate your sample?
b) How many rinses do they recommend? _______
c) Why should you not do what they recommend at the 2:23 mark during today’s lab?