1.4.1: Mass (Weight)

A. Mass (Weight)

The mass measurements may be performed with a 0.001gram precision balance (milligram balance) or a 0.0001 grams precision balance (analytical balance).

The balance should always be “zeroed” before anything is placed on the balance pan. On an electronic digital balance, this is done with the “tare” or “T” button.

Never place chemicals directly on the balance pan; place them on a porcelain container (evaporating dish) or watch glass outside of the balance prior to mass measurement. Clean up any materials you spill around the balance with a brush.

1.     Note the balance provided, as milligram balance or analytical balance. If the reading is 0.000 g on “tare” then you are using a milligram balance. If the reading in 0.0000 g on “tare”, then you have an analytical balance.

2.     Do the following, recording all the masses in the next three steps to the nearest 0.001 g with a milligram balance or 0.0001 g with an analytical balance. Since you are provided with a digital balance, record your measurements, so that all significant digits are measured.

3.   Request a solid rubber stopper from your instructor. Weigh the dry stopper. Save the stopper for part C of the experiment.

4.  Weigh a small evaporating dish (porcelain dish).

5.   Add approximately 5 g of sodium chloride to the evaporating dish from step 4. Measure to the nearest 0.001 g on a milligram balance or 0.0001 g on an analytical balance.

Note: Add the salt in small quantities with a spoon outside of the balance to reach approximately 5 g. Do not add the salt to the container while it sits in the balance. Clean up any materials you spill around the balance.

6.   Calculate the mass of sodium chloride by difference.

Observations:           

Balance used (Circle one):     Milligram Balance / Analytical Balance

Save the rubber stopper for part C and the salt for part B. Do not dispose.