## Lab: Moles, Molecules, and Grams

### Objective

In this lab we will measure the mass of five different chemicals and calculate the number of moles of each one and the number of molecules or atoms. By doing this lab you should get some practice doing the calculations, learn about relative numbers of molecules or atoms in different substances, and begin to see how the chemical unit of the mole can be useful.

### Materials 1. lab balance
2. lumps of aluminum (Al)
3. lumps of zinc (Zn)
4. sand (SiO2)

1. water (H2O)
2. sugar (C12H22O11)
3. weighing boat
4. 50-mL beaker

### Safety

• This lab presents few hazards but usual procedures for safety should be followed

### Pre-lab Questions

Answer the following questions before beginning the lab. Show work with units using calculations written in the form of a dimensional analysis conversion. Have your teacher read your responses and sign off below before moving on to the next section.

1. Find the molar mass of each of the five substances listed in the materials section of this lab. These will be your conversion factors for doing dimensional analysis conversions between the mass of a substance in grams and the number of moles.
2. Say you have 2.5 mol of H2O. How many grams is this?

How many molecules of H2O do you have?
3. Say you have 145.54 g of SiO2. How many moles is this?

How many molecules of SiO2 do you have?

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1. Say you have 2.107 × 1024 molecules of C12H22O11. How many moles is this?

How many grams of C12H22O11 do you have?

#### Check-in ______

When you have completed your work in this section check in with your teacher. This is a required part of the lab and your teacher’s initials are required before you can move on to the next section. Initials will be given for successfully demonstrating that you can perform the required calculations.

### Data Collection

In the space below construct a neat data table with the following headings: Name, Formula, Molar Mass (g/mol), Mass (g). Collect the data by obtaining samples of each substance from your teacher. Weigh each one to the nearest 0.01 g.

#### Check-in ______

When you have completed your work in this section check in with your teacher. This is a required part of the lab and your teacher’s initials are required to get full credit for this section. Initials will be given for successfully collecting all required data.

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### Lab Questions and Calculations

Answer the following questions and perform the following calculations. Answers must be in complete sentences. Show work for calculations.

1. Before you do any calculations which sample do you think has the largest number of atoms or molecules? Why?
2. Before you do any calculations which sample do you think has the smallest number of atoms or molecules? Why?
3. Calculate the number of moles of each substance based on the mass you measured.
4. Calculate the number of molecules or atoms of each substance based on the number of moles you calculated.
5. In the space below make a data table showing the Formula, Mass (g), Moles (mol), and Number of Atoms/Molecules. Put the results of your calculations in the table.

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1. Now that you have done the calculations, which sample had the largest number of atoms/molecules? Why wasn’t it the sample with the largest mass?
2. Now that you have done the calculations, which sample had the smallest number of atoms/molecules? Why wasn’t it the sample with the smallest mass?
3. Which sample has a greater number of moles: 100. g of sodium hydroxide (NaOH) or 100. g of krypton gas (Kr)?
4. You have the same mass of both chemicals in the previous question. Why didn’t you get the same number of moles?
5. You can count atoms within molecules, too. For example, one molecule of H2O has two atoms of H and 10 molecules of H2O has 20 atoms of H. Calculate the number of oxygen atoms in:
1. one molecule of N2O5
2. ten molecules of N2O5
1. a thousand molecules of N2O4
2. a mole of molecules of NO2
6. Moles are counting units. They perform the same function as counting how many items you have. How many moles of oxygen atoms do you have for each of the following?
1. one mole of N2O5
2. ten moles of N2O
1. 1.37 moles of NO2
2. 0.75 moles of N2O4
7. In order to react fully without leaving anything leftover every mole of oxygen gas (O2) must react with two moles of hydrogen gas (H2):
2H2 + 1O2 --> 2H2O

You have 64.00 g of O2 and 2.016 g of H2.

Is there enough H2 to react with the O2 you have?
(Hint: Convert grams to moles before attempting to answer the question).
Last updated: Mar 23, 2023       Home