Chemistry 1

INTRODUCTION TO MEASUREMENT

Introduction: In all chemistry experiments it is necessary to make certain measurements. In this exercise you will learn how to use a variety of measuring devices common to the chemistry lab. You will be measuring mass, volume, length and temperature. Each measuring device allows you to read a certain number of digits. If the device does not have a digital readout, you should estimate your measurement to one digit beyond those you can read directly from the scale. This last digit is the uncertain digit in your measurement. The precision of the device is assumed to be plus or minus one ( +1) in this last digit unless the device is labeled otherwise. You should pay careful attention to the precision of each device you use. Every measurement you make in the chemistry lab should reflect the maximum precision of the device.

Procedure: Mass: Your instructor will demonstrate the use of the balances in the lab. Obtain a piece of aluminum rod from the central table. Each rod has a number stamped into one end. Record the number on your data sheet. Choose a balance. Be sure to re-zero the balance before you begin. Determine the mass of the rod to +0.0001 g. Record the mass on your data sheet. Now choose another balance and determine the mass of the rod to +0.0001 g. Record this mass on your data sheet. Have your instructor verify that the mass you measured matches the value recorded on

the master list. You will need the same rod for the measurements in the next section. Determine the mass of the 10 mL graduated cylinder that is in your equipment drawer. Record the mass on your data sheet. Note: 1 mL = 1 cm

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Length: Take the ruler from your equipment drawer. Find the scale on the ruler. You will find large and small lines. What is the change in length between any adjacent small lines on the scale? What is the change in length between the large lines? Record these values on your data sheet. To what precision can you measure length using this device? Measure the length of the aluminum rod. Record this on your data sheet. Obtain a vernier caliper from the central table. Your instructor will show you how to use the caliper. What is the precision of the measurements made with this device? Measure the diameter of the rod in three different places along the length of the rod. Record these data on your data sheet. Calculate and record the average of these values. Replace the rod and caliper on the central table.

Volume: Look at the graduated cylinder. Find the scale on the side. You will find large and small lines. What is the change in volume between any adjacent small lines on the scale? What is the change in volume between the large lines? Record these values on your data sheet. To what precision can you measure volume using this device? Pour between 1 and 10 mL of water or acetone into your graduated cylinder. Determine the volume of liquid and record the volume on the data sheet. Do not empty the cylinder! Determine the mass of your cylinder and liquid. Record this mass on your data sheet.

Temperature: Obtain a temperature probe from the end drawer of your lab bench. Turn it on and observe the display. To what precision can you measure temperature using this device? Determine the temperature of the liquid in your graduated cylinder. Record this temperature on your data sheet. Discard the liquid from your cylinder into the sink.

Calculations: Calculate the density of the aluminum rod and the liquid. Ask your instructor how to locate the accepted values of the densities. Some formulas you will need:

Volume of a cylinder = r 2 h

r = radius of the cylinder h = height or length of the cylinder Density = _mass_ Volume Percent Error = |your answer – accepted answer| X 100% accepted answer

Date ______________ Section _______Name __________________________ Data and Calculations Sheet: Introduction to Measurement Data:

Number on Al rod

Mass Measurements

Mass of Al rod on first balance

Mass of Al rod on second balance

Mass of empty 10 mL graduated cylinder

Mass of 10 mL graduated cylinder with liquid

Length Measurements

Change in length between small lines on ruler

Change in length between large lines on ruler

Precision of ruler

Length of Al rod

Precision of caliper

Diameter of Al rod Measurement 1

Measurement 2

Measurement 3

Volume Measurements

Change in volume between small lines on graduated cylinder

Change in volume between large lines on graduated cylinder

Precision of graduated cylinder

Volume of liquid

Temperature Measurements

Temperature of liquid

Calculations: (You MUST show your work on a separate

sheet)

Average diameter of Al rod

Average radius of Al rod

Volume of Al rod

Density of Al rod

Identity of liquid (also fill in the space in the results section)

Mass of liquid

Density of liquid

Results: (You MUST show your work on a separate sheet)

Density of Al (your value)

Density of Al (accepted value)

Percent error

Density of (your value)

Density of (accepted value)

Percent error

Percent error = | your value – accepted value| X 100%

accepted value

Questions:

1. Was there a difference between the mass of the Al rod on the first balance and

the mass of the Al rod on the second balance? If yes, explain why this difference

might have occurred.

2. Think about the measurements you made today. Think about unavoidable errors

in the design of the experiment or the measuring devices. What are some errors

that may have caused your values of the density to differ from the accepted

value? Do not include mistakes such as misreading the ruler or

mathematics errors.

Date _______ Section ______ Name_________________________

ADVANCED STUDY ASSIGNMENT: Introduction to Measurement

1. State the number of significant figures in each of the following measured quantities.

a. 34.6743 g

b. 1.457 X 10 3 mm

c. 0.00579 cm 3

2. State the rule used to determine the number of significant figures in an expression involving only addition and/or subtraction. 3. State the rule used to determine the number of significant figures in an expression involving only multiplication and/or division.

4. Each of the following expressions contains only measured quantities. Evaluate each expression and report the answer with the correct number of significant digits and the appropriate units. In each case explain how you determined how many significant figures are in the answer. a. 4.5631 g + 3.91 g b. 22.3098 g - 5.9068 g c. 18.90 mL - 15.06 mL d. (22.3098 g -5.9068 g) (18.90 mL -15.06 mL) e. (34.8956 kg - 33.8956 kg) X (345.67 m/s + 4.5690 m/s)

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f. (203.339 g - 25.964 g) (50.00 mL - 26.35 mL)