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Measuring Mass

 

Purpose:

Practice the various techniques of measuring masses using the lab balance.  Gain experience in the techniques of handling laboratory materials and equipment.

 

Procedure:

            Part I Measuring Mass Directly

  1. Check your balance to make sure that the pointer is properly “zeroed”.  In an adjustment is necessary, consult your teacher.
  2. Place a penny on the balance pan.  Move the rider(s) until the pointer is balanced.  Record the mass of the penny
  3. Repeat step 2 for the objects listed below.  Record the mass of each object
    1. A nickel
    2. A watch glass
    3. A 150-ml beaker
    4. A 100-ml graduated cylinder

Part II Measuring Out a Substance

  1. Place a dry 50-ml beaker on the balance pan.  Move the riders until the pointer is balanced.  Record this reading
  2. Move the riders until they read exactly 22.0g more than the reading you obtained in step 4.  Record this setting
  3. In a 100-ml graduated cylinder, obtain exactly 30.0ml of cold tap water.  Slowly and carefully pour the water from the graduated cylinder into the beaker on the balance pan until the pointer is balanced.  Avoid splashing water onto the pan.  Note and record the volume of water remaining in the graduated cylinder.  Discard the water and dry the beaker.

Part III Determining Mass by Difference

  1. Measure and record the mass of a watch glass
  2. Using the procedure described by your teacher, obtain 20-25 crystals of calcium chloride (CaCl­2) n a piece of paper.  Carefully transfer the crystals to the watch glass.
  3. Measure and record the combined mass of the watch glass and calcium chloride.  Note and record the time of this measurement.
  4. Using your micro-spatula spread the crystals out on the watch glass.  Study the crystals and record your observations.  Set the watch glass and crystals aside to be reexamined later.
  5. Inflate a balloon and tie off the open end so that no gas can escape.  Measure and record the mass of the inflated balloon.
  6. Puncture the balloon and allow all the gas to escape.  Measure and record the mass of the deflated balloon.  Discard the balloon.
  7. Reexamine the calcium chloride crystals on the watch glass that you set aside earlier.  Record your observations.
  8. Measure and record the combined mass of the watch glass and its contents.  Note and record the time of this measurement.  Discard the calcium chloride and clean dry the watch glass.

 

Data / Observations:

            Part I

1) Mass of penny

2.50 g

2) Mass of nickel

5.02 g

3) Mass of a watch glass

24.68 g

4) Mass of 150-ml beaker

67.95 g

5) Mass of 100-ml graduated cylinder

46.34 g

Part II

6) Mass of 50-ml beaker

29.71 g

7) New setting (50-ml beaker  + 22.0g)

51.71 g

8)Volume of water remaining in graduated cylinder

7.0 ml

Part III

9) Mass of watch glass

24.68 g

10) Mass of watch glass + CaCl2

25.65 g

11) Time of measurement 9

1:28 pm - - 13:28

12) Mass of 150-ml beaker

67.95 g

13) Mass of 150-ml beaker + 30 ml of water

96.15 g

14) Mass of inflated balloon

1.60 g

15) Mass of deflated balloon

1.57 g

16) Mass of watch glass +CaCl2 (after sitting)

25.75 g

17) Time of measurement 14

1:48 pm - - 13:48

Calcium Chloride Crystals:

a-      initial examination

25.65g-24.68g=.97g          .97 grams of CaCl2

                        b- later examination

                              25.78g-24.68g=1.10g        1.10 grams of CaCl2

 

Calculations:

1 – Calculate the volume of water added to the beaker in step 6.

            30.0ml – 7.0ml = 23ml

                                                                        23ml of water added to beaker

2 – Calculate the mass of 1ml of water

           

                                                                        1ml of water = 9.40x10-1g

3 – Using the mass by difference calculate the mass of:

            a- CaCl2 crystals added to the watch glass

                        25.65g-24.68g=.97g

                                                                        .97g of CaCl2 crystals added to watch glass

            b- 30ml of tap water

                        96.15g-67.95g-28.20g

                                                                        28.20g=mass of 30ml of tap water

            c- moisture absorbed by CaCl2 crystals

                        25.75g-25.65g=.10g

                                                                        .10g of moisture absorbed by CaCl2 crystals

4 – Calculate the difference in mass between the inflated balloon and the deflated balloon

            1.60g-1.57g=.03g

                                                Difference in mass between inflated/deflated balloon = .03g

5 – Calculate how much time, in minutes, elapsed between the two measurements of the CaCl2.

             1:48pm            =          13:48

            -1:28pm           =          -13:28

             0.20 mins        =          00.20 mins

                                                            20mins elapsed between the two measurements

 

Questions:

1 – The difference between the mass of the balloon when inflated and its mass after being punctured is not an accurate determination of the mass of the gas in the inflated balloon.  Why is this?

This could be because when you inflated the balloon, the moisture from the exhale into the balloon could remain on the interior walls.  That moisture would then cause an inaccurate measure because it would be added to the mass of the balloon.

2 – Suppose you were asked to measure out 5 grams of calcium chloride, describe how you would make this measurement.

I would place the watch glass on a balance, and then zero out the balance with the watch glass placed in the tray.  After the balance is balanced with the watch glass, I would move the weights to represent an added five grams.  I would then slowly add calcium chloride to the watch glass until the balance rebalances or zeroes out.

3 – Suppose that you wanted to know the mass of a quantity of orange juice that was poured into a drinking glass.  Describe how you would determine this mass.

First, you would have to determine the mass of the glass without the juice in it.  Then, you would need to measure the drinking glass with the orange juice added.  In order to determine the mass of the orange juice alone, you would have to then use the mass by difference formula and subtract the mass of the glass from the measurement of the glass with the orange juice.  Your number that you get would be the mass of the orange juice.

4 – A beaker contains a quantity of a liquid.  You want to know the combined mass of the beaker and the liquid.  Describe how you would go about making this determination.

In order to make this measurement, you would just have to place the beaker with the liquid onto the tray of a balance.  The mass the balance reveals is the combined mass of the beaker and the liquid.

Conclusion:

            The measuring of mass can be very useful in finding and performing equations about other characteristics of materials.  Also, you can use the lab balances to mass water and other liquids by the process described in this lab, which is measuring the holding device and then subtracting that from the mass of the holding device and the liquid.  Last, when calcium chloride is exposed to the laboratory environment, the mass of the material will increase due to the fact that it absorbs the gasses and moisture from the environment.