Metric Measurements

Exercise 3:  Measurements of Mass and Temperature 

The basic metric unit for weight is a gram (g), which is equal to 0.03 of an ounce. One thousand grams equals a kilogram (kg), which is equal to 2.2 pounds. There are many types of scales and balances used in labs, the most common being the digital scale.

Kelvin is the SI unit for temperature used in chemistry and physics. Biology generally uses degrees Celsius (°C). Refer to Table 1 for the equations needed to convert degrees Celsius and Kelvin.

Table 1 – Temperature conversion equations

Some common temperatures to remember in Celsius are:

• Ambient temperature 23°C
• Human body temperature 37°C
• Freezing point of water at standard conditions for temperature and pressure (STP) 0°C
• Boiling point of water at STP 100°C.

PROCEDURE 

Digital Scale 

1.      To use the digital scale, first turn the scale on.

2.      Tare the scale.

NOTE: Taring is the process of re-zeroing the scale.

4.      Place a pen on the scale. Record the mass in Data Table 2.

5.      Place a piece of paper on the scale that can cover the entire tray of the scale.. Record the mass of the paper in Data Table 2.

Data Table 2 – Mass of objects

6.      Tare the scale so the mass of the paper is not counted along with the substance to be measured.

7.      Weigh out 2 g of sugar or salt onto the weigh paper and record the mass in Data Table 2.

8.      Weigh three additional objects of choice and record their masses in Data Table 2.

Thermometer 

NOTE: Follow these rules when working with a thermometer:

·        Be sure that the thermometer is placed in a secure area within the lab table so that it does not roll.

·        Never stir with the thermometer.

9.      Set out three small coffee cups or heat resistant cups.

10.      Label the cups hot, room temperature, and ice.

11.      To one cup, add very hot water from the faucet, until the cup is ½ full. Place the thermometer into this cup.

12.      Add room temperature water to the remaining two cups, until the cups are ½ full.

13.      To the third cup, add ice cubes.

14.      After five minutes read the temperature of the hot water using the Celsius scale. Record the temperature in Data Table 3.

15.      Place the thermometer into the cup of water at room temperature. Let it equilibrate for five minutes, then record the temperature in Celsius in Data Table 3.

16.      Move the thermometer to the ice cup. Allow it to equilibrate for five minutes. Record the temperature in Data Table 3.

Data Table 3 – Water temperatures