### All AP Chemistry Resources

## Example Questions

### Example Question #1 : Other Solution Concepts

A solution on NaCl has a denisty of 1.075 g/mL. If there are 0.475 L of solution present, what is the mass?

**Possible Answers:**

**Correct answer:**510.6 g

1.075 g / **mL** * 0.475 **L**

First, convert to mL

1.075 g / **mL** * **475 mL** = 510.6 g

### Example Question #2 : Other Solution Concepts

5L of 0.1M NaCl and 10L of 0.2M NaI are combined in a single vessel.

What is the final concentration of sodium ions in solution?

**Possible Answers:**

**Correct answer:**

NaCl and NaI are both highly soluble; thus both solutions can be treated as containing separate ions of sodium, chloride, and iodide.The final concentration can be found by finding the total number of moles of sodium ions and the total volume from both solutions.

We can find the moles of sodium ions from each solution by multiplying the volume by the molar concentration.

The total moles of sodium ions is:

Divide this by the total solution volume to find the final concentration:

### Example Question #3 : Other Solution Concepts

Given that the pKa of acetic acid is 4.76, what is the percentage of the protonated form of acetic acid in a solution where the pH is 6?

**Possible Answers:**

There is not enough information given

**Correct answer:**

In order to solve this problem, we first must use the Henderson-Hasselbalch equation:

Since we are given the pH of the solution and the pKa of acetic acid, we are able to solve for the ratio of conjugate base to acid:

Now that we have the ratio of conjugate base to acid, we need to calculate the percentage of the acid, or protonated form, in solution. To do this, it's important to realize that for every 17.38 moles of conjugate base, there is 1 mol of acid. Therefore, the total amount of acetic acid + acetate is equal to 18.38.

### Example Question #4 : Other Solution Concepts

Suppose that two containers, and , contain equal amounts of water. If 5 moles of is added to solution and 5 moles of glucose is added to solution , which solution will experience a greater increase in boiling point?

**Possible Answers:**

Both solutions will exhibit the same change in boiling point

Neither solution will experience a change in boiling point

Solution , because glucose has a greater molar mass than

Solution , because is able to dissociate into and ions, thus resulting in a greater amount of particles dissolved in solution

There is not enough information to answer the question

**Correct answer:**

Solution , because is able to dissociate into and ions, thus resulting in a greater amount of particles dissolved in solution

In the question stem, we are told that equal molar amounts of and glucose are added to containers and , respectively. The change in boiling point of water is a colligative property that is dependent on the number of dissolved solute particles, regardless of their identity. The addition of 5 moles of will result in approximately 10 moles of dissolved solute, since each mol of can dissociate into two ions, according to the following reaction:

Glucose, on the other hand, does not dissociate and simply remains as intact molecules. Thus, the addition of 5 moles of glucose to container results in 5 moles of dissolved solute. Since solution contains approximately twice as many dissolved solute particles as does solution , it will experience a greater increase in the boiling point of water.

### Example Question #5 : Other Solution Concepts

Approximately what is the pH of a solution of at ?

**Possible Answers:**

There is insufficient information to answer the question

**Correct answer:**

We are given the concentration of in solution and asked to find the pH. To do this, we must make use of the following equation:

It is also important to realize that is a strong base and will thus dissociate completey according to the following reaction:

Thus, for every one mol of that reacts, an equal number of moles of will be produced. And since there are to begin with, then will be produced.

Remember that this calculated value so far is the pOH, not the pH! To calculate the pH, it is vital to remember that at . Thus,

### Example Question #6 : Other Solution Concepts

What volume of water must be added to 750mL of 0.050M sodium chloride () in order to achieve a final concentration of 0.015M?

**Possible Answers:**

**Correct answer:**

For a solution of known volume and concentration (molarity in this case), the volume needed to dilute the solution to a desired concentration may be found using the formula:

Where and are the initial and final concentrations, and and are the initial and final volumes. So, for 750mL (0.750L) of a 0.050M solution diluted to 0.015M:

Solving for :

Now that we know the *total *volume needed, we may find the volume that must be *added* by subtracting the initial volume () from the final volume ():

1.75L of water must be added to 750mL of 0.050M in order to achieve a final concentration of 0.015M

### Example Question #7 : Other Solution Concepts

What is the pH of a 0.025M solution of hydrochloric acid ()?

**Possible Answers:**

**Correct answer:**

Since is a strong acid, calculations should be carried out assuming that the compound dissociates completely:

and are produced in a 1:1 ratio to total dissolved , so the concentration of in solution is the same as the concentration of :

pH is related to the concentration of :

### Example Question #8 : Other Solution Concepts

What is the osmotic pressure of a 5.0M solution of at ?

**Possible Answers:**

**Correct answer:**

Osmotic pressure is represented by:

Where Van’t hoff factor, , gas constant , temperature in . The Van’t hoff factor is a unitless number that represents the amount of ionic species that the compound will dissociate in solution. is part of a large group of molecules classified as hydrocarbons which normally do not dissociate at all in solution. Therefore, .

Plug in known values and solve.

### Example Question #1 : Other Solution Concepts

A solution was prepared by dissolving 22.0 grams of in water to give a 110mL solution. What is the concentration in molarity of this solution?

**Possible Answers:**

**Correct answer:**

In order to calculate the concentration, we must use molarity formula:

We must use the molecular weight of to calculate the moles of solute:

### Example Question #1 : Other Solution Concepts

A solution was prepared by dissolving 40.0 grams of in water to give a 50mL solution. What is the concentration in molarity of this solution?

**Possible Answers:**

**Correct answer:**

In order to calculate the concentration, we must use molarity formula:

We must use the molecular weight of to calculate the moles of solute:

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