Determining Number Without Counting

Chemists and chemical engineers usually need to control the number of

atoms, molecules, and ions in their reactions carefully. These particles are too small to be seen and too numerous to count, but their numbers can be determined by measuring their masses. Simulate this process by determining the approximate number of small, identical items in a large bag by weighing instead of counting.

PURPOSE: TO DETERMINE THE APPROXIMATE NUMBER OF SMALL, IDENTICAL ITEMS BY WEIGHING.

HYPOTHESIS:

MATERIALS: BEANS, BAGS, PENNIES, BUTTONS, WASHERS, BBS, BALANCE, CALCULATOR

PROCEDURE:

1. Count out a convenient number of items and weigh them. Record the number of items and the mass.

2. Weigh and record the mass of an empty, self-sealing plastic storage bag.

3. Completely fill the bag with items and seal it. (THIS STEP IS DONE FOR YOU)

4. Weigh and record its mass.

5. Develop and carry out a procedure to determine the number of items in the bag without opening it.

6. Repeat for each sample.

OBSERVATIONS:

SAMPLE

STEP 1

STEP 2

STEP 4

STEP 5

# OF ITEMS

ANALYSIS:

1. How many items are in each bag?

2. Explain how you determined that number.