STATISTICAL EVALUATION OF PENNIES

General Rules for the use of an Analytical Balance

1. Keep the balance and the area around it clean.

2. Never weigh anything heavier than the capacity of your balance (160 g.)

3. Make sure the object being weighed is at the same temperature as the balance.

4. Do not handle the object being weighed with your fingers, and do not rub glass objects with a cloth prior to weighing.

5. Never weigh chemicals directly on the metal weighing pan. We will use the 'weighing by difference' method whenever the analytical balance is used. The mass of sample is determined by the difference between an initial and a final weight.

6. Before using the balance for the first time that day, make sure that you calibrate the balance.

7. Whenever using the balance make sure the doors to the breeze shield are closed.

8. When you have finished weighing, make sure: a) The weight is recorded in your lab notebook; b) The balance is clean; c) Nothing is left on the pan; and d) The balance is off.

9. If the balance does not behave properly tell the instructor as soon as possible.

Procedure After a demonstration of the proper use of the analytical balance weigh by difference 10 pennies to the nearest 0.1 mg (0.0001 g), recording each mass in your laboratory notebook. Calculate the mass of each penny, and determine if any of the masses should be rejected by using the Q test. For the remaining data set calculate the mean, standard deviation (s), RSD in ppt, and the confidence interval for the mean at the 90% confidence level. Values for the Q test and the confidence interval can be found in your textbook.

Report Report all results on the form provided. Remember to show sample calculations on the back of your report.

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