Chemistry-Lab

Measurement:

Glassware, Techniques, and Measurement

Purpose

The purpose of this experiment is to learn how to identify and select appropriate laboratory equipment to make

measurements of length, temperature, volume, and mass.

Learning Objectives

Name and identify the purposes of common laboratory equipment.

Select appropriate equipment based on the precision, accuracy, and capacity of the measurement

needed.

Select the appropriate equipment to measure temperature, volume, and mass.

Explain proper safety measures used for handling common laboratory glassware and equipment.

Calculate the density of a liquid or solid from measured masses and volumes.

Calculate a range of experimental values.

Evaluate the accuracy of measurements by calculating percent error of an average of experimental

values from a literature value.

Evaluate precision of measurements by calculating the standard deviation of sets of measurements.

Laboratory Skills

Use an open analytical balance (digital balance).

Use graduated cylinders, pipets, and burets.

Use rulers and/or calipers.

Use thermometers.

Estimate the uncertain digit when recording measurements.

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Glassware, Techniques, and Measurement

Equipment 1 digital scale (500 g

capacity)

1 100 mL beaker

1 250 mL beaker

Ring stand

1 buret

1 10 mL graduated

cylinder

Thermometer

60 mL of unknown

solution

1 50 mL graduated

cylinder

Chemicals 30% NaCl(aq)

Introduction

Measurement in the Lab

There are a variety of instruments used to measure quantities such as temperature, volume, and mass in the

chemistry laboratory. The appropriate instrument or glassware is chosen based on the type of measurements

required for a particular experiment.

Measuring devices display a scale indicated by lines (on glassware) or a certain number of decimal places (on

balances). It is important to read and interpret these scales accurately. All values recorded from laboratory mea-

suring devices must reflect the precision and accuracy of the equipment being used. This is done by recording

the proper number of significant figures. Always consider significant figures when making measurements. Be

mindful that there are always uncertainties involved when making measurements.

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Glassware, Techniques, and Measurement

Measuring Temperature

Figure GM.1: Using Thermometers.

Thermometers are instruments calibrated to measure the tem-

perature of whatever surrounds the bulb or probe. Commonly,

thermometers are glass tubes filled with mercury or colored al-

cohol. They operate on the principal that the liquid inside them

will expand as it heats up and contract as it cools, thus providing

a measure of the temperature of its surroundings. Always record

one more digit than there are lines on a thermometer. For the

thermometer shown in Figure GM.1, the temperature should be

reported as 44.5∘C.

Measuring Volume

A variety of glassware is used to contain or deliver liquids in the

laboratory. Themost common types of glassware used in the gen-

eral chemistry laboratory are beakers, graduated cylinders, and Erlenmeyer flasks. General glassware, such as

beakers and Erlenmeyer flasks, provide only an approximate measure of volume and cannot be used when pre-

cision and accuracy are a concern.

Figure GM.2: The position of meniscus must al- ways be measured at eye level.

Volumetric laboratory glassware, which includes pipets,

burets, and volumetric flasks, is calibrated by theman-

ufacturer and used to measure volumes in the labora-

tory. Whenever recording volumes from volumetric

glassware, it is important to read the value correctly.

A characteristic of liquids in glass containers is that

they curve at the edges. This curvature is referred to

as themeniscus. When aqueous liquids are in glass

container, the meniscus will curve up at the edges and

down in the center. To read the volume correctly, your

eye must be level with the top of the liquid and you

must record the volume at the bottom of the menis-

cus, as shown in Figure GM.2.

Graduated cylinders are designed to contain a range of volumes of a liquid. They are marked with a vertical scale

along their length and measure volume by measuring the height of a column of liquid. A graduated cylinder

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Glassware, Techniques, and Measurement

with a small diameter is more accurate than one with a large diameter. Pipets and burets are glass tubes that are

calibrated “to deliver” (TD) a very precisely known amount of liquid at a given temperature. They are usually

marked with the amount, the precision with which they can deliver that amount, and the temperature at which

the pipet or buret was calibrated. Various types of glassware are illustrated in Figure GM.3. Volumetric glassware

is designed to measure one specific volume of liquid.

a b c d e

Figure GM.3: Volumetric glassware: a) graduated cylinder b) volumetric pipet c) graduated pipet d) buret e) volumetric flask.

Density – A Physical Property of Matter

Why do some objects sink, and other objects float when they are tossed into water? The answer to this question

can be explained by the concept of density. Density is a physical property, and it is an important intrinsic quantity

that is often used to help identify substances in the chemistry laboratory. The formal definition of density is the

ratio of an object’s mass per unit volume, as shown in Equation GM.1:

density = mass volume (Equation GM.1)

Water has a density of ~ 1.0 g/mL. An object with a density less than water ( < 1.0 g/mL) will float, and an object

with a density greater than water ( > 1.0 g/mL) will sink.

The density of a solid is normally expressed in grams per cubic centimeter (g/cm3), the density of a liquid in

grams per cubic centimeter or grams per milliliter (g/mL), and the density of a gas in grams per liter (g/L). To

determine the density of a substance, measure both the mass and volume of a sample and divide the mass by the

volume, as indicated in Equation GM.1.

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Glassware, Techniques, and Measurement

Figure GM.4: A digital laboratory balance.

Mass measurements are performed using a variety of balances, chosen for the pre-

cision and capacity required for the procedure. A common type of laboratory bal-

ance, a digital balance, is shown in Figure GM.4.

The mass of a sample or object can be determined directly or by difference. In

direct weighing, the sample or object is placed directly on the balance pan and the

mass is recorded. To determine the mass by difference, first measure and record

themass of an empty container. Then add the sample or object to the container and

record the combined mass. Subtract the initial mass (the empty container) from

the final mass (container + sample) to obtain the mass of the sample or object.

Percent Error

In this laboratory, you will make measurements to determine the density of a known substance. The density of a

pure substance is an intensive property of matter because it does not depend on the amount of substance being

measured. However, measurements in the laboratory always include some uncertainty and, thus, there is always

some amount of error in measurements and values calculated from those measurements.

You will compare your calculated density with the known density for the substance by calculating the percent

error in your determination. Percent error is defined Equation GM.2:

Percent Error = |Experimental Value − Accepted Value|

Accepted Value × 100% (Equation GM.2)

Recall that vertical lines in an equation specify the absolute value of the number within

them.

Because the difference between the experimental and accepted value is expressed as an absolute value, percent

error is always a positive quantity.

Procedure

Part I Density of Unknown Liquid

1. Obtain a 100 mL beaker and put about 60 mL of unknown solution into it.

2. Weigh a clean dry 10mL graduated cylinder on an analytical balance. Record themass using the appropriate

number of significant figures and units. (Use the same balance for future weighing to ensure accuracy in

mass recordings.)

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Glassware, Techniques, and Measurement

3. Pour 10 mL of solution into the 10 mL graduated cylinder and weigh it on the same analytical balance used

previously. Record the mass using the appropriate units and number of significant figures. Make sure to

look at the volume reading and record your observation.

4. Empty and dry the graduated cylinder. Repeat this process four more times for a total of five trials.

Part II Density of Water

1. Inspect the equipment provided at your bench and identify the buret, beaker, and balance.

Figure GM.5: Buret clamped to a ring stand.

2. Properly prepare and fill the buret with deionized

water (DI water) (Figure GM.5).

3. Look at the lines on your buret. Note that the

markings on the buret start with 0.00 mL at the

top! Read the volume to one-hundredth if a

milliliter, which is two places past the decimal:

for example, 1.01 mL. Record this initial volume.

4. Record the mass of an empty 100 mL beaker.

5. Dispense a small volume of DI water into your

pre-weighed beaker. Youmay choose any volume

of to dispense between 3 and 5mL. Read themass

of the beaker +water on an analytical balance. Record themass using the appropriate number of significant

figures and units.

6. Record the final volume in the buret, to two decimal places.

7. Empty the beaker and measure the mass of the empty beaker.

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Glassware, Techniques, and Measurement

8. Add a new sample of water (3 – 5 mL) into the beaker and record the volume dispensed.

9. Measure the mass of the beaker + water and record it in the data table.

10. Dispense three more samples of water as described for a total of five separate volume and mass measure-

ments.

11. Pour about 50 mL of DI water into the beaker. Measure and record the temperature of the water.

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Glassware, Techniques, and Measurement

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Report Sheet:

Glassware, Techniques, and Measurement

Name:

Section: Date:

Part I Density of Unknown Liquid Mass of empty graduated cylinder (g)

Report Table GM.1: Graduated Cylinder Measurements

Trial 1 Trial 2 Trial 3 Trial 4 Trial 5

Mass of graduated cylinder and liquid (g)

Mass of liquid (g)

Volume of liquid (mL)

Density (g/mL)

Part II Density of Water Mass of empty beaker (g)

Report Table GM.2: Buret Measurements

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5

Initial volume of buret (mL)

Final volume of buret (mL)

Volume of water dispensed (mL)

Mass of beaker and water (g)

Mass of water dispensed (g)

Density (g/mL)

Temperature of DI water (°C)

Catalyst Education OER Labs are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 license. To access our full list of experiments visit https://links.labflow.com/OER. Lab Version GM Release 3.28. GM.1