5 Steps to a 5 AP Chemistry

Give yourself 1 point for the correct equation, or for any other correct calculation.

Do not give yourself more than 2 points total for this part.

b. Pwater=25.2 mm Hg/760 mm Hg =0.0332 atm. Tand Vare the same as in part a.

Avogadro’s number =6.022 × 1023 molecules mol−^1 =N

n=PV/RT

=(0.0332 atm ×0.1900 L)/(0.0821 L atm mol−^1 K−^1 ×299 K)

=2.57 × 10 −^4 mol H 2 O)

molecules =(2.57 × 10 −^4 mol) ×(6.022 × 1023 molecules mol−^1 )

=1.55 × 1020 molecules

Give yourself 1 point for the correct answer (no deduction for rounding

differently). You must include allparts of the calculation (including “=”).

Give yourself 1 point for the correct equation, or for any other correct calculation.

Do not give yourself more than 2 points total for this part.

c. (0.00742 mol H 2 ) ×(2.016 g H 2 /mol H 2 ) =0.0150 g H 2

(2.57 × 10 −^4 mol H 2 O) ×(18.02 g H 2 O/mol H 2 O) =0.00463 g H 2 O

total mass =0.0150 g H 2 +0.00463 g H 2 O =0.0196 g

density =0.0196 g/0.1900 L =0.103 g/L

Give yourself 1 point for the correct answer (no deduction for rounding

differently). You must include allparts of the calculation (including “=”).

Give yourself 1 point for the correct equation, or for any other correct calculation.

Do not give yourself more than 2 points total for this part.

d. 0.00742 mol H 2 and 2.57 × 10 −^4 mol H 2 O

total moles =(0.00742 +2.57 × 10 −^4 ) =0.00768 mol

Mole fraction H 2 O =(2.57 × 10 −^4 mol H 2 O)/(0.00768 mol)

=0.0335

Give yourself 1 point for the correct answer (no deduction for rounding

differently). You must include allparts of the calculation (including “=”).

Give yourself 1 point for the correct equation, or for any other correct calculation.

Do not give yourself more than 2 points total for this part.

Total score =sum of parts a–d. If any of the final answers has the incorrect number

of significant figures, subtract one point.

Second Free-Response Question

a. 2 KClO 3 (s) → 2 KCl(s) +3 O 2 (g)

You get 1 point if you have the above equation.

b. (2/3 mole KClO 3 ) (3 moles O 2 /2 moles KClO 3 ) =1 mole O 2

You get 1 point for the correct answer and 1 point for the work. You can get these

points if you correctly use information from an incorrect equation in part a.

c. At STP the volume of 1 mole of O 2 should be 22.4 liters. The volume is greater because

oxygen was not the only gas in the sample. Water vapor was present. The presence of

the additional gas leads to a larger volume.

You get 1 point for discussing STP and 22.4 liters, and 1 point for discussing the

presence of water vapor.

d. There are two acceptable equations; either will get you 1 point. You do not need both

equations.

120  Step 4. Review the Knowledge You Need to Score High