5 Steps to a 5 AP Chemistry

Question 6.

(a) Beaker B has the lowest pH. The NH 4 +ion is the conjugate acid of a weak base, and as an acid (weak)

it will lower the pH.

You get 1 point for the correct beaker. You get 1 point for the explanation.

(b) Solutions A and B produce a gas with a characteristic odor when mixed. The reaction is:

NH 4 +(aq) +OH–(aq) →NH 3 (g) +H 2 O(1)

or

(NH 4 ) 2 SO 4 (aq) +Ba(OH) 2 (aq) →2 NH 3 (g) +2 H 2 O(1) +BaSO 4 (s)

You get 1 point for the correct two solutions, and you get 1 point for either of the balanced equations.

(c) Solution C has the lowest freezing-point depression. This solution is the only nonelectrolyte present.

The electrolytes depress the freezing point to a greater extent.

You get 1 point for the correct solution, and 1 point for the explanation.

(d) Solutions A and D. You get 1 point for each of these you get correct.

(e) Solution C will give no precipitate. Beaker B gives BaSO 4. Beaker D gives Ba 3 (PO 4 ) 2. Beaker E gives

Fe(OH) 2 and BaSO 4.

You get 1 point for choosing solution C. You get 1 point for listing the other precipitates or explaining

that beaker C contains a nonelectrolyte that will not react with either barium ions or hydroxide ions.

Total your points for the different parts. There are 10 possible points.

TOTAL SCORE:

Question 1 ————

Question 2 ————

Question 3 ————

Question 4 ————

Question 5 ————

Question 6 ————

AP Chemistry Practice Exam 2  343