Parents and students: Please read these instructions and make sure that anyone performing experiments works with adequate supervision and care. I expect everyone to show up next week with all skin and digits intact!
Goal: Develop basic chemistry lab skills.
Equipment: (If you are substituting equipment, please see the chemistry lab list for appropriate substitutes).
Read the safety rules. Be sure that you understand them.
If necessary, reassemble your equal arm scale. If your scale is strong enough, use it for all of the following exercises. If not, use a postal scale or diet scale for the exercises involving larger masses.
Add a nickel (standard 5gm mass!) to each side of the scale.
Joggle one side of the scale slightly, and watch the swing range of your pointer against the grid. How far does it swing to the left? [WRITE IT DOWN!] How far to the right? If the swings are equal, you are well-balanced. If not, adjust your arm slide to make the swings equal. Repeat the test at least twice.
Place a known mass on the scale, of sufficient weight to read 20% of the scale range. For example, if you have a 100g scale, put something which is at least 20g (4 nickels would do it) on it.
Joggle the scale, and watch it come back to equilibrium. Does it read correctly? If not, adjust the scale so that it reads properly. Then repeat the test 2 more times.
Be sure to record all your measurements for the exercise below.
|Trial||Dry tube/stopper||Dry beaker||volume of water||Mass of Tube + water||Mass of tube + beaker||Mass of water|
Dry all your equipment. Recalibrate your scale and repeat ALL your measurements two more times.
Estimate the amount of error in your measurements and suggest how you might reduce it.
If your water looks muddy, filter it again.
Examine your filter paper.
If you have heat-resistant glass, you may want to try evaporating your filtered salt solution.
Why didn't we just boil the salt water in the beaker above the flame?
POURING AND DECANTING
This technique is commonly used for pouring from large-mouthed vessels into smalle ones. It takes some practice, so be prepared for spills.
With practice, you can do this quickly and without spills. So practice!
Lab report: Please send me your table for the mass measurements with your scale, along with your recommendations for how you could improve the accuracy of your mass measurements.
If you are seriously interested in doing much home chemistry, I highly recommend the book Explorations in Chemistry by Charles A Gray.
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