### All College Chemistry Resources

## Example Questions

### Example Question #1 : Molarity, Molality, Normality

A solution is prepared by dissolving in of water. The final volume of the solution is . Find the concentration of the solution in units of molality.

**Possible Answers:**

**Correct answer:**

Recall how to find the molality of a solution:

First, start by finding the moles of glucose that we have. The molar mass of glucose is .

Next, convert the grams of water into kilograms.

Now, plug in the moles of glucose and kilograms of water into the equation for molality.

### Example Question #1 : Molarity, Molality, Normality

A solution of hydrogen peroxide is by mass. What is the molarity of the solution? Assume that the solution has a density of .

**Possible Answers:**

**Correct answer:**

Start by assuming that we have of this solution. Recall that hydrogen peroxide has a molecular formula of .

Use the given density to find the mass of the solution.

Next, find the mass of the hydrogen peroxide present in the solution.

Convert the mass of hydrogen peroxide into moles of hydrogen peroxide.

Recall how to find the molarity of a solution:

Since we have of solution, the molarity is .

### Example Question #1 : Molarity, Molality, Normality

What is the molarity of a solution in which sodium hydrogen carbonate is dissolved in a solution?

**Possible Answers:**

**Correct answer:**

sodium hydrogen carbonate dissolved in a solution has .

The first step is to calculate how many moles of are present.

We calculate molarity with the following equation:

### Example Question #1 : Molarity, Molality, Normality

How many milliliters of a solution are needed to prepare of ?

**Possible Answers:**

**Correct answer:**

of solution are needed to prepare of .

We can use the formula

Therefore,

### Example Question #1 : Molarity, Molality, Normality

What are the concentrations of aluminum and sulfate in a 3.0 M solution of aluminum sulfate?

**Possible Answers:**

**Correct answer:**

The relative concentrations of aluminum sulfate are

### Example Question #1 : Molarity, Molality, Normality

Which of the following choices is characteristic of molality?

**Possible Answers:**

Equivalents per liter

Useful in experiments without significant temperature changes

Moles of solute per liter of solution

Useful in experiments with significant temperature changes

**Correct answer:**

Useful in experiments with significant temperature changes

Molarity, molality, and normality are all units of concentration in chemistry. Molarity () is defined as the number of moles of solute per liter of solution. Molality () is defined as the number of moles of solute per kilogram of solvent. Normality () is defined as the number of equivalents per liter of solution. Molality, as compared to molarity, is also more convenient to use in experiments with significant temperature changes. This is because the volume of a solution increases with temperature, and heating causes molarity to decrease; however, since molality is based on masses rather than volumes, molality remains unchanged.

### Example Question #1 : Molarity, Molality, Normality

What is the molality of a solution made by adding of to of water?

**Possible Answers:**

**Correct answer:**

Molality () is defined as moles of solute per kg of solvent.

is the solute (it is what is being dissolved) and water is the solvent (what is doing the dissolving).

Let’s start converting of to moles by dividing by its molecular weight using scientific notion through the entire molality calculations as necessary to simplify calculations.

Now we must convert the of water to then divide by it to get the molality:

Molality of solution:

=

### Example Question #1 : Molarity, Molality, Normality

What is the molarity of a solution containing of solution containing of ?

**Possible Answers:**

**Correct answer:**

Molarity moles of solute per liter of solution.

We are given that there are of and of solution.

First lets convert the of solution to liters. It is easiest to use scientific notion in all calculations for easy simplification:

=

Now we must convert of to moles to get moles of solute per liter of solution.

This is done by dividing by its molecular weight which is . Once again we can use scientific notion to simplify calculations:

Now we can divide by solution to get the molarity.

### Example Question #1 : Molarity, Molality, Normality

How many of water are needed to dilute to ?

**Possible Answers:**

**Correct answer:**

In order to solve for the volume of water needed we must use this equation:

solve for since we are looking for the final volume of water needed to dilute the existing solution: