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Chemistry |
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MEASURING MASS
There are various types of laboratory balances. The triple beam beam balance you use may look somewhat different from the one in the Figure below, however all beam balances have some common features.
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Carrying the Balance
1. Be sure all riders are back to the zero point.
2. Place one hand under the balance and the other hand on the support (arm) to carry the balance.
Using the Balance
1. Zero the balance before you determine the mass of any substance.
a) Slide all of the riders
back to the zero point.
b) Check to see that the pointer swings freely along the
scale.
c) Use the
adjustment screw to obtain an equal swing of the beams, if necessary. You do not have to wait for the pointer to stop at the zero point. The
beam should swing an equal distance above and below the zero point.
2. Never put a hot object directly on the balance pan. Any dry chemical that is to be massed should be placed on paper or in a container. Never pour chemicals directly on the balance pan. Remember to mass the paper or container before adding the substance.
3. Once you have placed the object to be massed on the pan, move the riders along the beams beginning with the largest mass first. If the beams are notched, make sure all riders are in a notch before you take a reading. Remember; the pointer does not have to stop swinging, but the swing should be an equal distance above and below the zero point on the scale.
Lab Instructions
1. Zero the balance.
2. Obtain 15 pennies and find their collective mass to the nearest thousandth of a gram
(xx.xxx).
3. Record the data properly.
4. Calculate an average mass keeping the measurement to the nearest thousandth
of a gram. Show your work.