Friday, September 30, 2011
Monday, September 26, 2011
Homework Help Gas Collection Problems
Consider the following problem:
A 500 mL sample of oxygen was collected over water at 23°C
and 760 torr pressure. What volume will the dry oxygen occupy at 23°C and 760
torr? The vapor pressure of water at 23°C is 21.1 torr.
What are we solving for? V2
Plan: 1 - Use Dalton's Law to find P02
2 - Use Combined Gas Law to solve for V2
PTOTAL =
POXYGEN - PWATER
POXYGEN
= 760 torr – 21.1 torr
POXYGEN
= 738.9 torr
Given: V1
= 500 mL V2 = ? (No change in T)
P1 = 738.9 torr P2
= 760 torr
V2
= P1V1 T2
(Temperature can cancel as there is
no change.)
P2
T1
V2
= (500 mL) (739 torr) = 486 mL dry O2
(760
torr)
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