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.

- lab balance
- lumps of aluminum (Al)
- lumps of zinc (Zn)
- sand (SiO
_{2})

- water (H
_{2}O) - sugar (C
_{12}H_{22}O_{11}) - weighing boat
- 50-mL beaker

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

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.

- 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.
- Say you have 2.5 mol of H
_{2}O. How many grams is this?

How many molecules of H_{2}O do you have? - Say you have 145.54 g of SiO
_{2}. How many moles is this?

How many molecules of SiO_{2}do you have?

- Say you have 2.107 × 10
^{24}molecules of C_{12}H_{22}O_{11}. How many moles is this?

How many grams of C_{12}H_{22}O_{11}do you have?

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.

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.

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.

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

- Before you do any calculations which sample do you think has the largest number of atoms or molecules? Why?
- Before you do any calculations which sample do you think has the smallest number of atoms or molecules? Why?
- Calculate the number of moles of each substance based on the mass you measured.
- Calculate the number of molecules or atoms of each substance based on the number of moles you calculated.
- 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.

- 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?
- 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?
- Which sample has a greater number of moles: 100. g of sodium hydroxide (NaOH) or 100. g of krypton gas (Kr)?
- You have the same mass of both chemicals in the previous question. Why didn’t you get the same number of moles?
- You can count atoms within molecules, too. For example, one molecule of H
_{2}O has two atoms of H and 10 molecules of H_{2}O has 20 atoms of H. Calculate the number of oxygen atoms in:

- one molecule of N
_{2}O_{5} - ten molecules of N
_{2}O_{5}

- a thousand molecules of N
_{2}O_{4} - a mole of molecules of NO
_{2}

- one molecule of N
- 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?

- one mole of N
_{2}O_{5} - ten moles of N
_{2}O

- 1.37 moles of NO
_{2} - 0.75 moles of N
_{2}O_{4}

- one mole of N
- In order to react fully without leaving anything leftover every mole of oxygen gas (O
_{2}) must react with two moles of hydrogen gas (H_{2}):

2H_{2}+ 1O_{2}--> 2H_{2}O

You have 64.00 g of O_{2}and 2.016 g of H_{2}.

Is there enough H_{2}to react with the O_{2}you have?

(Hint: Convert grams to moles before attempting to answer the question).