AP Chemistry : Solutions

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #7 : Precipitates And Calculations

The  of  (at 298K) is . What is the molar solubility of the hydroxide ion () in a saturated solution of ?

Possible Answers:

Correct answer:

Explanation:

The dissociation of calcium hydroxide in aqueous solution is:

The  of calcium hydroxide is related to the dissolved concentrations of its counterions:

 and  are produced in a molar ratio of 1:2; for each molecule of calcium hydroxide that dissolves:

Given a  value of , the molar solubilities of each counterion may be determined by setting . It follows that:

Now, we can use basic algebra to solve for :

Since we set , and , multiplying the value of  by two gives the correct answer, which is 0.022M.

 

Example Question #1 : Precipitates And Calculations

What type of reaction is also known as a precipitation reaction?

Possible Answers:

Double replacement

Single replacement

Combustion

Combination

Decomposition

Correct answer:

Double replacement

Explanation:

Double replacement reactions can be further categorized as precipitation reactions since it is possible to make a precipitate (solid) from mixing two liquids. Combustion reactions involve using oxygen to burn another species, and the products are carbon dioxide and water. Combination reactions involve the synthesis of one molecule from two separate ones; decomposition is the opposite. 

Example Question #1 : Solubility And Equilibrium

Calculate the molar solubility of AgBr in 0.050 M AgNO3 at room temperature.  The Ksp of AgBr is 5.4 x 10-13.

Possible Answers:

1.08 M

2.16 M

1.08 x 10-11 M

1.57 x 10-12 M

2.16 x 10-11 M

Correct answer:

1.08 x 10-11 M

Explanation:

Example Question #1 : Solubility And Equilibrium

Would the molar solubility of Cr(OH)3 increase or decrease as the pH is lowered (i.e. made more acidic)?

Possible Answers:

Increase

There is no change

Decrease

Can not be determined

Correct answer:

Increase

Explanation:

Since Cr(OH)3 is a basic salt, decreasing the pH makes it more soluble.

Example Question #2 : Solubility And Equilibrium

Calculate the molar solubility of SrF2 in 0.023M NaF.  The Ksp for SrF2 is 4.3 x 10-9.

Possible Answers:

3.2 x 10-3 M

3.2 x 10-5 M

8.1 x 10-6 M

5.2 x 10-4 M

1.6 x 10-3  M

Correct answer:

8.1 x 10-6 M

Explanation:

Example Question #41 : Solutions

Calculate the molar solubility of Mn(OH)2 at pH 9.5.  The Ksp for Mn(OH)2 is 1.6 x 10-13.

Possible Answers:

2.1 x 10-5 M

1.5 x 10-3 M

1.6 x 10-4 M

2.4 x 10-3 M

3.5 x 10-4 M

Correct answer:

1.6 x 10-4 M

Explanation:

Example Question #42 : Solutions

Calculate the molar solubility of CaF2 (Ksp  = 3.9 x 10-11) in a room temperature solution of 0.010 M Ca(C2H3O2)2.

Possible Answers:

1.6 x 10-2 M

3.2 x 10-2 M

3.1 x 10-5 M

4.2 x 10-4M

3.7 x 10-4 M

Correct answer:

3.1 x 10-5 M

Explanation:

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:
0.510 g
2.263 g
2.2 g
510.6 g
441.9 g
Correct answer: 510.6 g
Explanation:

1.075 g / mL * 0.475 L 

First, convert to mL

1.075 g / mL475 mL = 510.6 g

Example Question #43 : Solutions

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:

Explanation:

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 #1 : 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:

Explanation:

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.

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