I need help with Eudiometer problems I dont know how to do them

[spectravoid]

Ok well we are on gas laws. I understand dalton's law of partial pressures, and the ideal gas law, and graham's law

 

but i got to Eudiometer problems, and now i'm stuck. I just dont know what to do. I tried to devise my own formula but most of my answers end up 1/100 of the actual answer. How do you answer these types of questions. Can you solve these questions and say/show how/why

 

 

#1. The volume occupied by oxygen gas collected over water at 25 degrees Celcius and at an atmospheric pressure of 740 mm Hg is 155 mL. What would the volume be if the oxygen gas was separated from the water vapor and then placed in a cylinder at a pressure of 740 mm Hg?

 

Answer: 150 mL (if you get this answer tell me how)

 

#2. If 10.8 Liters of a gas collected over water has a total pressure of 0.97 atm at 24 degrees Celcius, what will be the volume of the dry gas at STP?

 

Answer: 9.34 L

 

#3. 300 mL of a gas is collected in a eudiometer over water at a temperature of 27 degrees Celcius. The barometer reads 775 torr and the water level inside the eudiometer is 7.2 cm higher than the outside level. Determine:

a) The pressure of the wet gas

b) The pressure of the dry gas

C) The volume of the dry gas at STP

 

Answers: 770 torr, 743 torr, 267 mL respectively

 

#4. 4.00 g of CH4 and 11.00g of CO2 are collected in a eudiometer over water at 25 degrees Celcius and a barometric pressure of 740 torr. The water level inside the eudiometer is 136 mm higher than the outside water level. Determine the partial pressures of all gases in the tube

 

Answer: 353 torr CH4, 353 torr CO2, 23.7 torr H2O

 

#5. 35 mL of H2 were collected in a eudiometer over Hg. The Hg level inside the tube was 40 mm higher than the Hg level outside the tube. The temperature was 25 degrees Celcius and the barometric pressure was 740 mm Hg. Correct the volume of the H2 to STP. How many moles of H2 were in the tube?

 

Answer: 29.5 mL, 0.00130 moles

 

Table Values

PH2O at 25 degrees Celcius = 23.76 mm Hg

PH2O at 27 degrees Celcius = 26.74 mm Hg

PH2O at 24 degrees Celcius = 22.38 mm Hg

[John Cuthber]

OK, In the first question the measured pressure is 740mmHg but that's a mixture of water vapour and oxygen.

The table at the end says that the water vapour is 23.76 mm so the true pressure of oxygen is only 740-23.76 ie 716.24 mmHg

So you really only have 155 * 716.24/740 =150 ml of oxygen measured at 740mm.

Does that help?

[CaptainPanic]

About question 2,

What is STP?

 

I can't find the solution which gives the answer 9.34 liters. And I(should) know how to use the ideal gas law, and partial pressures.

 

About question 3 part 1:

10 meter water = 1 bar

7.2 cm water = 720 Pa = 5 mm Hg

(you can also say: the density of Hg is 13.5x the density of water: 7.2/13.5 = 0.5 cm = 5 mm.

So, the pressure is lower because the pressure is higher. This means that the pressure is 775 - 5 = 770.

 

About question 3 part 2:

The partial pressure of water at 27 deg C is 26.74 mm Hg

P(water) = 26.74 mm Hg

P(total) = P(water) + P(dry gas)

P(dry gas) = P(total) - P(water) = 770 - 26.74 = 743.3 mm Hg

 

About question 3 part 3:

Again, I cannot figure it out. What's this STP?