Quiz 4-26-12

1
Quiz 4-26-12

• Answers

2
2.30 g Na are reacted with 100.0 mL of 0.10 M
phosphoric acid. Calculate the number of liters
of hydrogen gas formed at STP.
6 Na 2H3PO4 ? 3 H2 2 Na3PO4
2.30 g Na
1 mole Na
3 mole H2
22.4 L H2
1.12 L H2
23.0 g Na
6 mole Na
1 mole H2
3
2.30 g Na are reacted with 100.0 mL of 0.10 M
phosphoric acid. Calculate the number of liters
of hydrogen gas formed at STP.
6 Na 2H3PO4 ? 3 H2 2 Na3PO4
0.100 L H3PO4
0.1 mole H3PO4
3 mole H2
22.4 L H2
0.336 L H2
1L H3PO4
2 mole H3PO4
1 mole H2
4
When you actually perform the experiment, you get
0.30 L of H2. What is the percent yield.

• The two values for the volume of H2 were 0.336 L
  and 1.12 L of H2
• 0.336 L is the theoretical yield. 1.12 is just
  wishful thinking.
• 0.30 L is the actual yield.

Actual yield
0.30 L H2
X 100
89
theoretical yield
0.336 L H2
5
A 0.336 L of sample of hydrogen gas at STP is
heated to 23oC at 745 mm Hg.Calculate the volume
of the gas at room temperature.
Identify the variables V1 0.336 L T1 273 K P1
760 mm Hg T2 23 273 296 K P2 745 mm
Hg V2 ?
P1V1 P2V2
T1 T2
P1
V1
T2

V2
T1
P2
(760 mm Hg)
(0.336 L)
(296 K)
0.372 L
(273 K)
(745 mm Hg)