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

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. 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.
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 60.08 g of SiO₂. How many moles is this?
   
   
   
   
   How many molecules of SiO₂ do you have?

4. 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.

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.

6. Now that you have done the calculations, which sample had the largest number of atoms/molecules? Why?
7. Now that you have done the calculations, which sample had the smallest number of atoms/molecules? Why?
8. Which sample has a greater number of moles: 100. g of sodium hydroxide (NaOH) or 100. g of krypton gas (Kr)?
9. You have the same mass of both chemicals in the previous question. Why didn’t you get the same number of moles?
10. 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).