# Molar Masses

BACKGROUND

Here is an example of how to make up a W/V solution, to give you an idea about the steps for the next exercise.

Using the salt provided to you, you can make a 50 ml of 5% (W/V) NaCl solution.

*Steps:

1. Get a clean 250ml-beaker ready;

2. Add about 35 ml dH2O to above beaker;

3. Weigh _______ grams of salt using an electronic balance;

4. Place weighted salt into a 50mL beaker and mix till the is dissolved completely;

5. Transfer all the salt solution to a 100mL graduated cylinder;

6. Adjust the volume to 50 ml by adding dH2O. Be sure to add distilled water a little by little and not more than the volume of 50 ml.

EXERCISE:

*Please help me with the following tasks, using the steps above to help you.

1. How many grams of EDTA (FW=292.25) are needed to make 0.5M solution? Describe how you will make the solution.

2. The formula weight of boric acid is 61.83, how many grams are needed to make 100mL of 0.6M solution? Describe how you will make the solution.

3. To make 10% (w/v) of ammonium persulfate solution, how many grams are required? (The formula weight of ammonium persulfate is 228.2). Describe how you will make the solution.

https://brainmass.com/chemistry/acids-and-bases/molar-masses-500062

#### Solution Preview

1. How many grams of EDTA (FW=292.25) are needed to make 0.5M solution? Describe how you will make the solution?

Useful Equations:

a. Solve for the mole of solute needed.

Use the equation:

Molarity = M = mole solute / volume of solution in liter

Hence,

Mole solute = Molarity x volume of solution in liter

b. Compute for the mass in gram of the solute needed.

Mass of solute in gram = mole solute x molar mass of the solute

Computation:

Assuming a volume of 100 mL for the solution:

Mole EDTA = 0.5 mole/L (0.1 L)

Mole EDTA = 0.05

Mass of EDTA = 0.05 mole (292.25 g/mole EDTA)

Mass of EDTA = 14.61 g

How to Prepare the Solution:

a. In a small beaker, weigh 14.61 g of EDTA using a chemical balance.

b. ...

#### Solution Summary

This solution helps answer various questions involving molar masses.