Lab 1: Measurement

Introduction

In this lab, you are asked to make a series of mass, volume and temperature measurements and record the number of significant figures and units in each measurement.

Mass measurement involves determining the mass of the sand in a vial.

Three stations will be set up in the laboratory. Each station is set up for you to determine the two volume measurements and a temperature measurement. The measuring instruments at the three stations are:

1.  a graduated cylinder for volume measurement

2.  a buret for volume measurement

3.  a temperature for temperature measurement

Volume measurements can be made with various types of glasswares. The glassware that is used determines the accuracy of the measurement.

In all the measurement determination, it is important that you pay attention to:

1.  the determination of the value of the measurement,

2.  the unit that is associated with the measurement,

3.  the proper number of significant figures that is associated with the measurement.

Introduction to the Analytical Balance

Weighing a sample is often the first step in many quantitative analytical methods. An analytical balance measures masses to within 0.0001 g. Balances are sensitive to drafts, changes in temperature, or the vibrations caused by moving people. The balances are stored in a separate room to minimize these variables and are placed on concrete tables. Balances are very expensive and are sensitive to attack by corrosive chemicals. Do not take liquid into the balance room. When possible, chemicals should be added to the weighing container outside of the balance chamber. It is important that you clean up all chemical spills.

In this experiment, you will learn to use the balance properly and be aware of the common errors.

Introduction to Volumetric Glassware

When performing a chemistry lab, the procedure may include using various types of glassware for volume measurements. In order to accurately perform the lab procedures, an understanding of the different types of glassware is required. Each piece of glassware is made to certain specifications. That is, there is a maximum measurement error associated with the glassware known as the tolerance. For example, a flask which holds 5.00 mL of liquid has a tolerance of ±0.02 mL (or ±0.4 %). This means that the actual volume that the flask holding is in the range of 4.98 to 5.02 mL. In order to avoid introducing a significant error to the analytical result, the tolerance specifications of each piece of volumetric glassware must match the required accuracy of the procedure.

The following is a summary of the various types of glassware and their tolerance.

Accuracy of the Various Types of Graduated Glasswares

Type of Glassware / Accuracy / Target Volume / Accuracy Range
Graduated Erlenmeyer flask / ± 10% / 100 mL / 100 mL ± 10 mL
roughly accurate
Graduated beaker / ± 5% / 100 mL / 100 mL ± 5 mL
roughly accurate
Graduated cylinder / ± 0.5% / 100 mL / 100 mL ± 0.5 mL
accurate
Volumetric flask / ± 0.1% / 100 mL / 100 mL ± 0.1 mL
very accurate
Volumetric pipet / ± 0.05% / 100 mL / 100 mL ± 0.05 mL
very accurate
Buret / ± 0.01% / 100 mL / 100 mL ± 0.01 mL
very accurate

Volume Measurements – Graduated Cylinder

In any volume measurement we need to approach the measuring instrument at proper eye position, at eye level. When we are up close to the liquid level at eye level, we will observe that the surface of the liquid forms a "lens-shaped". This is called the meniscus. In taking the measurement, we always read the bottom of the meniscus. Below is an example of a reading taken of a liquid in a graduated cylinder. The diagram shows an expanded view of the portion of the cylinder near the surface of the liquid.

/ Let's analyze this measurement:
1.  Upon inspection of the graduated cylinder, we observe that the finest division is a 1mL division.
2.  We can always make an estimate of a reading to within the finest division. Therefore, to the best of my judgement, I conclude that this particular graduated cylinder is able to provide a reading accuracy to ± 0.2 mL. (Note: A plus or minus 0.2 mL reading accuracy means that a volume measurement using this graduated cylinder will contain uncertainty in the first decimal place.)
3.  The bottom of the meniscus lines up with the 4th finest division above the 10 mL mark.
4.  The volume reading is determined to be 14.0mL. This volume reading has 3 significant figures. (Note: the '0' in this measurement is an uncertain figure. This measurement is accurate to 14.0 ± 0.2 mL. It means that using this graduated cylinder, the accuracy of the volume of the liquid is between 13.8 mL to 14.2 mL.)


Volume Measurements – Buret

In any volume measurement we need to approach the measuring instrument at proper eye position, at eye level. When we are up close to the liquid level at eye level, we will observe that the surface of the liquid forms a "lens-shaped". This is called the meniscus. In taking the measurement, we always read the bottom of the meniscus. Below is an example of a reading taken of a liquid in a buret. The diagram shows an expanded view of the portion of the buret near the surface of the liquid.

/ Let's analyze this measurement:
1.  Upon inspection of the buret, we observe that the finest division is a 0.1 mL division.
2.  We can always make an estimate of a reading to within the finest division. Therefore, to the best of my judgement, I conclude that this particular buret is able to provide a reading accuracy to ± 0.02 mL. (Note: A plus or minus 0.02 mL reading accuracy means that a volume measurement using this buret will contain uncertainty in the second decimal place.)
3.  The bottom of the meniscus lines up with the 6th finest division below the 34 mL mark.
4.  The volume reading is determined to be 34.60 mL. This volume reading has 4 significant figures. (Note: the '0' in this measurement is an uncertain figure. This measurement is accurate to 34.60±0.02mL. It means that using this buret, the accuracy of the volume of the liquid which has been dispensed is between 34.58 mL to 34.62 mL.)


Temperature Measurements – Thermometer

In any temperature measurement we need to approach the measuring instrument at proper eye position, at eye level. When we are up close to the mercury level at eye level, we will observe that the surface of the mercury forms a "lens-shaped" that bulges upward. This is called the meniscus. Unlike the meniscus that we observe with a liquid like water, the mercury forms a positive meniscus. In taking the measurement, we always read the top of the positive meniscus. Below is an example of a temperature reading. The diagram shows an expanded view of the portion of the thermometer near the surface of the mercury.

/ Let's analyze this measurement:
1.  Upon inspection of the thermometer, we observe that the finest division is a 1 oC division.
2.  We can always make an estimate of a reading to within the finest division. Therefore, to the best of my judgement, I conclude that this particular thermometer is able to provide a reading accuracy to ±0.2 oC. (Note: A plus or minus 0.2oC reading accuracy means that a temperature measurement using this thermometer will contain uncertainty in the first decimal place.)
3.  The top of the positive meniscus almost lines up with the 30 oC mark.
4.  The temperature reading is determined to be 29.8 oC. This temperature reading has 3 significant figures. (Note: the '8' in this measurement is an uncertain figure. This measurement is accurate to 29.8 ±0.2 oC. It means that using this thermometer, the accuracy of the temperature is between the range 29.6 oC to 30.0oC.)


Procedure

Note: Parts A, B, and C can be done in any order.

Part A: Mass measurement

1.  Place an empty weighing boat on the analytical balance and zero the balance.

2.  Obtain a vial of sand and carefully empty the content of the vial on the weighing boat.

3.  Record the mass of the sand and the unit of the measurement on the data sheet and determine the number of significant figures of the recorded measurement.

Part B: Volume measurements

Three stations are set up in the laboratory. At each station take:

1.  the volume reading of the buret

2.  the volume measurement of the graduated cylinder

3.  Record the volume measurements and the units of the measurements on the data sheet and determine the number of significant figures of the recorded measurements.

At the end of Part B, you should have recorded 6 volume measurements:

§  3 buret readings

§  3 volume measurements of the graduated cylinders

Part C: Temperature measurements

Three stations are set up in the laboratory. At each station take:

1.  the temperature reading of the thermometer

2.  Record the temperature measurements and the units of the measurements on the data sheet and determine the number of significant figures of the recorded measurements.

At the end of Part C, you should have recorded 3 temperature measurements.


Experiment 1 - Measurement

Name:______Date______

Data:

Part A: Mass measurement

Vial Number / Mass / Number of Significant Figures
Recorded in the Measurement

Part B: Volume measurements

Graduated Cylinder Measurement / Volume / Number of Significant Figures
Recorded in the Measurement
Station A
Station B
Station C
Buret Reading / Volume / Number of Significant Figures
in the Volume Dispensed
Station A / Final Reading:
Initial Reading: 3.55 mL
Volume Dispensed:
Station B / Final Reading:
Initial Reading: 0.80 mL
Volume Dispensed:
Station C / Final Reading:
Initial Reading: 1.00 mL
Volume Dispensed:

Part C: Temperature measurements

Thermometer Reading / Temperature (°C) / Temperature (K) / Number of Significant Figures
for the Temperature in Kelvin
Station A
Station B
Station C

Measurement.doc 9/19/2012 1-9