Mole Concept and Relative Mass

Introduction:

The relative mass of an object is how many times more massive that object is than some defined standard object. The atomic masses of the elements are all relative masses. The standard for atomic mass is 1/12 the mass of a carbon-12 nuclide. This mass, 1 amu., is roughly the mass of a hydrogen atom. Even though the standard for the atomic mass unit is based on Carbon-12, it is often more convenient for us to think of relative masses in terms of the smallest element, hydrogen. In this activity you will work with beans to develop the concept of relative masses. This should help you better understand the concept of the mole and of relative masses.

Objectives:

Develop an understanding of the mole concept and the concept of relative masses.

Calculate relative mass and the number of atoms in one relative mass.

Materials/Equipment:

Plastic cup / Zip top bags 1 each of lentils
Balance / chick peas
pinto beans
kidney beans

Safety Considerations:

·  Always wear goggles in the lab.

Procedure:

Part A

1.  Determine the mass of exactly 100 beans of each type by weighing them in a cup of known mass. Do not use any bean that differs greatly from the average bean (broken, misshapen).

2.  Record these masses as they are measured.

3.  Calculate (DO NOT WEIGH) the mass of one bean of each type. Record these values.

4.  Use the following formula to determine the relative mass of each type of bean:

Relative Mass =

5.  Calculate the number of beans in one relative mass of each bean by dividing the average mass of one bean into the relative mass.

Number of beans in 1 relative mass =

6.  Check your calculated results by adding beans to a cup of known mass until the total mass of the beans in the cup is equal to the sum of the mass of the cup and the relative mass of that type of beans. If you can tare your balance, just tare the cup and add beans until the mass is that of one relative mass for that type of beans.

7.  Count the beans. Record this as the measured number of beans in one relative mass.

8.  Pour the beans out into a separate pile so that you will be able to answer questions about them later.

9.  Repeat this for each type of beans.


Name ______

Partner’s Name(s) ______

Period ______Date______

Data:

Mass of empty cup before activity
Mass of empty cup after activity
Bean 1 / Bean 2 / Bean 3 / Bean 4
Name (type)
Mass of 100 beans plus cup
Mass of 100 beans
Average mass of one bean
Relative Mass of beans
Calculated # beans in one relative mass
Measured # beans in one relative mass

Questions:

1.  What did you discover about the number of beans in one relative mass? How did your calculated values compare to your measured values?

2.  How many times larger is the chick pea relative mass than the lentil bean relative mass? How does this relate to the number of beans in the relative mass?

3.  Explain why there are always the same numbers of beans in one relative mass.

4.  Are the volumes of the relative mass piles the same? Why or why not?

5.  What is the average mass of the lightest bean? What is the relative mass of the lightest bean?

6.  Among the elements, hydrogen has the least massive atoms-an atom of hydrogen has an average mass of 1.66 x 10-24 g. This is very small, but it is the mass of only ONE ATOM. What is the relative mass of hydrogen if it is the least massive element?

Name ______

Partner’s Name(s) ______

Period ______Date______

Part B

Average masses of individual atoms are reported in the chart below. Calculate the relative mass of each element and record it in the chart. Then look up the molar mass of each element on the Periodic Table and record that in the chart.

Atom
/ Mass of
one atom (g) / Mass relative to H / Atomic Mass
(look up) / # atoms in a relative mass
Hydrogen (H) / 1.66 x 10-24
Carbon / 2.00 x 10-23
Iron / 9.30 x 10-23
Aluminum / 4.49 x 10-23
Zinc / 1.08 x 10-22
Lead / 3.44 x 10-22
Copper / 1.05 x 10-22

Although this calculation works with a relative mass of hydrogen of 1.00 as its basis, atomic masses are actually calculated relative to a particular type of carbon atom viewed as exactly 12.00.

Questions:

1.  How do the atomic masses found on the Periodic Table compare to the relative masses you calculated?

2.  What are atomic masses and how are they determined?

3.  What did you discover about the number of atoms of each element in one relative mass?

4.  One atomic mass unit (amu) is the approximate mass of a proton or neutron. This mass is equal to 1.66 x 10-24 grams. How many atomic mass units are in one gram?

ASIM Mole Concept and Relative Mass p. 1

Revised: 2/06