Experiment 1 – Measurements Name __________________Lab Section __________________

Experiment 1 – Measurements

Introduction

Measurements are made on a daily basis, many times without thinking about it. How tall are you? How much orange juice is in that glass? How hot was it yesterday? How much does this backpack full of books weigh? How long until lab the pasta is ready? All of these questions are answered by measuring a quantity. In the aforementioned cases, length, volume, temperature, mass, and time were being measured. Depending on how well the measurement device is, a better or worse value can be reported.

In science the metric system is used for measuring these quantities. It is a simple and effective measurement system based on powers of ten and uses five base measurements to quantify physical properties. These five base measurements are length, volume, temperature, mass, and time. They are represented by the quantities meter (m) or centimeter (cm), liter (L) or milliliter (mL), temperature (°C or K), gram (g) or kilogram (kg), and seconds(s), respectively.

Though measurement tools become better and better all the time, there is still some uncertainty in any measurement that is made. As you will see in this lab, depending on what measurement tool you use, the precision to which you can report the value will change. Some numbers will be very precise, others not as much. How good the measurement too is will be reflected in the amount of significant figures you can report in the value.

Every measuring device has a given uncertainty in its measurement. A centimeter ruler is only valid out to the nearest ±0.1cm, while the millimeter ruler is valid out to the nearest ±0.05 cm. A graduated cylinder is valid to the nearest ±0.5 mL, and a thermometer has an uncertainty of ±0.5°C. Each of the measuring devices listed above involve a human estimation of equipment, that is to say a judgment call of “just where the end or meniscus lay” is involved. The balance is the only measurement tool where the estimation has been done by the machine, and the number reported requires no estimation. What is reported by the balance is what you record. In the case of the milligram balance, the error is ±0.001 g. Below you will find examples of each of these measurements.

After all base measurements have been made; compound units can be derived from these. Units such as speed (length per time), density (mass per volume), and volume derived from lengths (e.g. cm3) can be calculated and their values reported. This utilizes the rules for determining significant figures, and your number should be reported as such.

Experiment 1 – Measurements Name __________________Lab Section __________________

Examples

Measuring with Ruler

Centimeter Ruler

Since the markings on the centimeter ruler are only every integer, the object can only be read to within ±0.1 cm.

5.3 cm

Millimeter Ruler

There are finer gradations on the millimeter ruler, allowing for a more precise measurement of the object. Here the tenths measurements are clearly marked, and the estimation of the measurement can be made out to ±0.05 cm.

5.35 cm

Experiment 1 – Measurements Name __________________Lab Section __________________

Measuring with a Graduated Cylinder

When liquid is placed into a graduated cylinder a meniscus is formed. A meniscus (from the Greek meniskos, meaning “lunar crescent”) is a concave formation of the water in the tube. Measurements are made from the bottom of the meniscus. Due to how the gradations are marked on the cylinder, a measurement of only ±0.5 mL can be reported,

60.0 mL 46.5 mL

Measuring with a Thermometer

Due to the gradations on the thermometer, it is only possible to record temperatures to ±0.5°C.

26.5°C 20.0°C

Experiment 1 – Measurements Name __________________Lab Section __________________

Reading a Buret

Just like a graduated cylinder, a buret has a meniscus and much be read in a similar fashion. The error on a buret, however, is ±0.05 mL.

31.65 mL

Calculating Volumes from Length Measurements

Centimeter Ruler

A rectangular solid was measured using a centimeter ruler. It measured 2.5 cm by 1.2 cm by 11.1 cm. What is the volume of the solid?

(2.5cm ) (1.2cm ) (11.1cm )=33.3cm3→33cm3

Note: the least amount of significant figures in the original data is two. Following the rules for significant figures, the volume should only be reported to two significant figures.

Millimeter Ruler

A rectangular solid was measured using a centimeter ruler. It measured 2.55 cm by 1.20 cm by 11.15 cm. What is the volume of the solid?

(2.55 cm ) (1.20 cm ) (11.15cm )=34.119 cm3→34.1cm3

Note: the least amount of significant figures in the original data is three. Following the rules for significant figures, the volume should only be reported to three significant figures.

Experiment 1 – Measurements Name __________________Lab Section __________________

Procedure

Mass Measurements

For all mass measurements, perform the following procedure. Tare (zero) the balance and wait until it reads 0.000 g. Place the indicated item on the balance and record its mass. The three items to weigh are: a pencil, an Erlenmeyer flask, and a 100 mL beaker.

Length Measurements

Measure the length of a credit card, small test tube, and a watchglass using both the centimeter and millimeter rulers. It is easiest to measure the diameter of the watchglass by placing it “hump up” on the ruler. Be sure to keep the correct precision of each ruler in your data (i.e. one decimal place for the centimeter ruler, two for the millimeter ruler).

Temperature Measurements

Read the temperature of a thermometer sitting at room temperature.

Read the temperature of a thermometer sitting in an ice bath. Note, you may need to stir the batch to remove any temperature gradients. If so, wait until the mark is stable and record the temperature.

Read the temperature of a thermometer in boiling water

Note: all temperature measurements can be made to within ± 0.5°C

Experiment 1 – Measurements Name __________________Lab Section __________________

Volume Measurements

Partially fill a 100 mL beaker with water. Record the volume of water you put into the beaker. Note: you should not be able to indicate anything more than precision in the tens place.

Fill a 100 mL graduated cylinder to nearly ¾ full. Record this volume. Pour out some water and rerecord the volume. Pour out yet more water and rerecord the volume. Note: a graduate cylinder can be read to within ± 0.5 mL.

Read the volume on the partially filled buret provided to you by your instructor. If the bottom of the meniscus is difficult to read, place your hand behind the buret, or use a reading card. Note: the buret can be read to within ± 0.05 mL

Unknown Solid

Obtain an unknown solid from your instructor.

Record its mass and measure its length, width, and height dimensions using both the centimeter and millimeter rulers.

Calculate the volumes you obtain from the different ruler measurements of the solid’s dimensions. Be sure to use significant figures.

Equipment Needed:

PencilErlenmeyer flask100 mL beaker

Credit card/I.D. cardSmall test tubeWatchglass

Graduated CylinderUnknown sample

Experiment 1 – Scientific Measurements Name __________________Lab Section __________________

Prelaboratory Questions

What are the five base measurements and their units?

What is meant by “uncertainty”? Please give an example.

What are the uncertainties of all quantities you will measure in this lab?

In the figures below, please indicate the value that would be reported.

Experiment 1 – Scientific Measurements Name __________________Lab Section __________________

Data Table

Mass Measurements

Mass of a pencil

Mass of an Erlenmeyer flask

Mass of a 100 mL beaker

Length Measurements

Length of credit card

Centimeter ruler

Millimeter ruler

Length of small test tube

Centimeter ruler

Millimeter ruler

Diameter of watchglass

Centimeter ruler

Millimeter Ruler

Temperature Measurement

Room Temperature

Ice Water Bath

Boiling Water

_________________ g

_________________ g

_________________ g

_______________ cm

_______________ cm

_______________ cm

_______________ cm

_______________ cm

_______________ cm

_______________ °C

_______________ °C

_______________ °C

Experiment 1 – Scientific Measurements Name __________________Lab Section __________________

Volume Measurement

Volume inside 100 mL beaker

Volume inside graduated cylinder

- Minus first pour

- Minus second pour

Volume inside buret

Unknown Solid

Mass of solid

Volume of solid

Length of solid – centimeter ruler

Width of solid – centimeter ruler

Height of solid – centimeter ruler

Volume of solid – show calculation

Volume of solid

Length of solid – millimeter ruler

Width of solid – millimeter ruler

Height of solid – millimeter ruler

Volume of solid – show calculation

_______________ mL

_______________ mL

_______________ mL

_______________ mL

_______________ mL

________________ g

_______________ cm

_______________ cm

_______________ cm

_______________ cm3

_______________ cm

_______________ cm

_______________ cm

_______________ cm3

Experiment 1 – Scientific Measurements Name __________________Lab Section __________________

Postlaboratory Questions

1) Please indicate how many significant figures are in the following numbers:

152 __________ 0.0031 __________ 100.0 __________

1001 __________ 0.120 __________ 1500.08 __________

15000 __________ 0.03040 __________ 105000 __________

2) Perform the following calculations and report the answer in correct significant figures:

157.231 g 149.735 g 1500 cm 950 mL+ 43.51 g - 31.1 g + 10 cm - 10 mL

(0.55 cm)(10.1 cm) 149.175 g (48.25 cm)(19.1 cm)(0.50 cm) 25.5 mL

3) The ball of iron below weighs 55.265 g and measures 3.00 cm in diameter. What is the

density of the iron ball? (V= 43r 3, where r is the radius)