AP Chemistry : AP Chemistry

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #411 : Ap Chemistry

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:

Explanation:

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 #51 : Solutions

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

Possible Answers:

Correct answer:

Explanation:

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 #97 : Solutions And States Of Matter

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

Possible Answers:

Correct answer:

Explanation:

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 #98 : Solutions And States Of Matter

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:

Explanation:

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 #411 : Ap Chemistry

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:

Explanation:

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 #91 : Solutions And States Of Matter

How many milliliters of solution is needed to dissolve 5 grams of  to prepare a solution of concentration 10M?

Possible Answers:

Correct answer:

Explanation:

In order to calculate the number of milliliters, we must first determine the number of moles in 5 grams of  using its molecular weight as a conversion factor:

Using the concentration units as a conversion factor and the number of moles calculated, the number of milliliters can be calculated:

Example Question #11 : Other Solution Concepts

A solution was prepared by diluting 10mL of a 0.500M salt solution to 20mL. What would be the final concentration of this solution?

Possible Answers:

Correct answer:

Explanation:

Use the dilution formula:

Rearranging this equation gives:

Plugging in the values gives:

Therefore, after diluting the solution to 20mL, the solution concentration would be lowered from 0.50M to 0.25M.

Example Question #412 : Ap Chemistry

Which of the following is a weak electrolyte?

Possible Answers:

Correct answer:

Explanation:

Solutes that dissociate completely in a solution are called strong electrolytes. Weak electrolytes stay paired to some extent in solutions. As a result, strong electrolytes include ionic compounds and strong acid and bases.

Example Question #13 : Other Solution Concepts

Which of the following definitions is false?

Possible Answers:

Solubility product, , is the product of ion concentrations at equilibrium in a supersaturated solution of salt.

Ion-product constant of water, , is the product of equilibrium concentration of  and  ions in an aqueous solution at .

Molality is the number of moles of solute in a solution divided by the number of kilogram of solvent.

The van't Hoff factor, i, is the number of ions that a compound produces in a solution.

Correct answer:

Solubility product, , is the product of ion concentrations at equilibrium in a supersaturated solution of salt.

Explanation:

Solubility product, , is the product of ion concentrations at equilibrium in a saturated solution of salt. All other definitions are true.

Example Question #413 : Ap Chemistry

Balance the following equation:

NaOH + H2SO4 → H2O + Na2SO4

Possible Answers:

2 NaOH + H2SO4 → H2O + Na2SO4

2 NaOH + H2SO4 → 2 H2O + Na2SO4

NaOH + H2SO4 → H2O + Na2SO4

4 NaOH + 2 H2SO4 → 4 H2O + 2 Na2SO4

4 NaOH + H2SO4 → 2 H2O + 2 Na2SO4

Correct answer:

2 NaOH + H2SO4 → 2 H2O + Na2SO4

Explanation:

Balancing equations:

there is 1 NaOH and 1 H2SO4 in the reactants; and 1 H2O and 1 Na2SO4 in the products

steps:

1) balance the Na first; get 2 NaOH

2) balance H next; get 1 H2SO4, 2 H2O

3) check to make sure that O and S balance

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