5 Steps to a 5 AP Chemistry

Give yourself 1 point for each correct equation. The values 137.33 and 233.34 are

optional.

d. Lead would also precipitate as the sulfate. It would be necessary to remove the lead
before the sulfate was added.
Give yourself 1 point for this answer.
There is a total of 8 points possible.

Second Free-Response Question

a. A sample of sodium hydroxide is weighed and dissolved in deionized water to give a
solution of the approximate concentration desired. (Alternatively, a concentrated
NaOH solution could be diluted.)
Samples of dried KHP are weighed into flasks and dissolved in deionized water.
A few drops of the appropriate acid-base indicator (phenolphthalein) are added to
each sample.
A buret is rinsed with a little of the NaOH solution; then the buret is filled with
NaOH solution.
An initial buret reading is taken.
NaOH solution is titrated into the KHP samples until the first permanent pink color.
A final buret reading is taken.
Using the molar mass of KHP, determine the moles of KHP present. This is equal
to the moles of NaOH.
The difference in the buret readings is the volume of NaOH solution added (convert
this to liters).
The molarity of the NaOH solution is the moles NaOH divided by the liters of
NaOH solution added.
(Repeat the procedure for each sample.)
Give yourself 2 points for this entire list, if the items are in order. If three or more
items are in the wrong order or missing, you get only 1 point. You get 0 points for three
or fewer items.

percentage of barium

mass of barium in sample

=

()

(()

%

ma ss of origina l sa mp le

× 100

Experimental  299

pH 7

pH > 1

Volume Added

Equivalence point at pH < 7

You get 1 point for this graph. You get an additional point for noting that the equivalence

point is greater than 7.

b.