Indirect Measurement
TEACHER NOTES
COS Objectives:
Standard 1: Bullet 1 - Distinguishing between intensive and extensive properties of matter.
Lab Time: This depends on how you group the students. Students can work in small groups and indirectly determine one or more assigned quantities especially if time is limited. All of the problems take about the same amount of time to determine except for #3 involving evaporation of water. This one takes longer. This one might be required by all groups, or eliminated so that all students finish in approximately the same amount of time.
Preparation Time: Approximately 10 minutes to set everything out.
Considerations: The directions for students are deliberately vague to provide an opportunity for students to develop their own methods. It might be interesting to compare data collected by using different methods to determine the same quantity. Some suggested methods are included below in case the students need help.
Answers to Questions:
1. Mass of drop of water
Method 1: Mass added
a. Place a small container on a balance.
b. Zero the balance.
c. Add from a pipet a definite number of drops (at least 10).
d. Determine the total mass of the drops.
e. Divide to find the mass of one drop of water.
Method 2: Mass removed
a. Place a light weight container which large enough to hold a pipet horizontally on the balance.
b. Fill a pipet with water.
c. Place the pipet on the container.
d. Weigh container and filled pipet.
e. Remove a definite number of drops from the pipet (at least 10).
f. Reweigh the container and partially filled pipet.
g. Subtract the weights and calculate the average mass of one drop of water.
2.Volume of drop of water
a. Place an exact amount of water in a graduated cylinder.
b. Fill a pipet with water.
c. Add water dropwise to the graduated cylinder counting the drops until exactly one milliliter has been added.
d. Calculate milliliter per drop by dividing 1 mL by the number of drops added.
3. Evaporation mass change
a. Mass a clean, dry crucible.
b. Add water to the crucible until it is ½ full.
c. Reweigh.
d. Heat strongly for 2 minutes.
e. Allow to cool.
f. Reweigh.
g. Calculate grams of water lost and percent mass lost.
4. Thickness of paper
a. Measure the thickness of a known number of pieces of paper and divide. It is best if the paper has never been separated.
5. Diameter of copper wire
a. Look up the density of copper.
b. Weigh the piece of copper.
c. Calculate the volume of copper using D=m/v
d. Calculate the radius by using V=πr2
e. Determine the diameter using d=2r
*Note the volume of copper can also be determined using water displacement.
6. Diameter of lead shot.
a. Any type shot can be used as long as the pieces are uniform in shape.
b. Crease a piece of paper.
c. Place a known number of pieces of shot on the crease. Make sure they are touching, but in a single line.
d. Mark the ends of the line of shot on the paper.
e. Measure the length of the line and divide by the number of pieces of shot.
7. Number of kernels of popcorn (or grains of rice)
a. DO NOT OPEN THE CLOSED BAG! The mass contained in the bag should be printed on it.
b. Weigh a known number of kernels (or grains).
c. Calculate kernels/g by dividing the number of kernels by their mass.
d. Calculate the number of kernels in the bag by multiplying the mass of bag in grams by the kernels / g.