Name: ______________________________
Counting by Weighing Pre-Lab Date: ________________ Class: _________
1.
What is the basic atomic difference between isotopes of the same element?
2.
If there are 100 navy beans, 27 pinto beans, and 173 black eye peas in a container, what is the percent composition of the container by bean?
3.
If your chemistry grade is broken down so that 70% of it is based on exams, 20% on lab reports, and 10% on homework, and your average scores (out of 100 points in each area) are:
Exams – 85, labs – 75, and homework – 96
What would your weighted average be?

Name: ______________________________
Counting by Weighing Lab Date: ________________ Class: _________
1.
Count 40 whole peas. Record their total mass. This is one “batch.”
1 batch = 4.01g
2.
Calculate the mass that you would expect 200 peas to have (using factor-label):
3.
Place peas on the balance until their mass is equal to your answer in #2. Then count the peas and record the amount: 205 peas
4.
Using 200 peas as the accepted value and your answer to #3 as your experimental value, calculate the percent error.
5.
Count 40 whole beans. Record their total mass. This is one “batch.”
6.
Calculate the mass that you would expect 200 beans to have (using factor-label):
1 batch = 8.09g
7.
Place beans on the balance until their mass is equal to your answer in #6. Then count the beans and record the amount: 210 beans
8.
Using 200 beans as the accepted value and your answer to #7 as your experimental value, calculate the percent error.

Fill in the following box with YOUR DATA to define the mass of a “batch” of peas or beans:
_____40_______peas = 1 batch peas = _____4.01______ g
_____40______beans = 1 batch beans = _______8.09_____ g
Perform the following calculations using sig figs. Show all work and use the
1.
What is the mass of 0.88 batches of peas?
2.
How many peas would be present in 175 g of peas?
3.
How many beans are there in 1.72 batches of beans?
4.
What would be the mass of 828 beans?
5.
64.0 g of beans is how many batches?
6.
How many batches are contained in 1040 peas?
7.
How many grams would be needed to obtain 40,000 peas?
8.
How many grams are needed to obtain 40,000 beans?