Questions are below please help I'm having a lot of trouble... Please show work and explanation and answer thank you!

Question

Question #1
An 811 mL sample of hydrogen was selected over water at 21.0 degrees celsius on a day when the barometric pressure was 759 torr. What volume would the dry hydrogen occupy under standard conditions? The vapor pressure of water at 21.0 degrees celsius is 19.0 torr.

Question #2
What is the volume occupied by 5 g of gaseous H2S at 171 degrees celsius and 1086 torr?

Question #3
Two gases are contained in gas bulbs connected by a valve. Gas A is present in a 1 liter bulb at a pressure of 811 torr. Gas B exerts a pressure of 277 in a 1 liter bulb. The valve is opened and the two gases equilibrate. What is partial pressure of gas A expressed after equilibration.

Question #4
A gas at 73 degrees celsius occupies 4.35 L. At what temperature will the volume be 3.89 L, assuming the same pressure?

Answer 1

Hi Laynie

 

For these problems you have to assume ideal gas behavior so you can use the ideal gas law PV = nRT.

It is also important that you remember the following conversions as they may not be given.

 

1 atm = 760 mmHg = 760 torr = 101325 Pa

 

Question 1

First you need to find the partial pressure of hydrogen. To do that you need to use the following equation

P_total = P_hydrogen + P_water

You're given P_total = 759 torr and P_water = 19 torr so you can find P_hydrogen

P_hydrogen = P_total - P_water = 759-19 = 740 torr = 0.9737 atm

To find the volume of hydrogen at standard conditions (1 atm and 25 degrees celsius) you need to use the ideal gas law. First write down which values you're given and which ones are not known.

 

P_1 = 0.9737 atm                           P_2 = 1 atm

T _1= 21 degrees +273 = 294 K      T_2 = 25+273= 298 K

V_1 = 811 mL = 0.811 L                  V_2 = ?

 

From the ideal gas law: PV = nRT you should notice that n and R (universal gas constant) are constants which allows you to write the following:

P_1*V_1/T_1 = P_2*V_2/T_2

Solving for V_2 gives V_2 = (0.9737)(0.811)(298)/(1)(294)= 800 mL

 

Question 2

You first need to find the moles of H2S. 

Molecular weight of H2S (from the periodic table) = 34.09 g/mol

moles of H2S = 0.14667

Write down what information is given to you

P = 1086 torr = 1.4289 atm

T = 171 + 273 = 444 K

n = moles of H2S = 0.14667

R = 0.08206 L.atm/K.mol

V = ?

Then use the ideal gas law to find V

V = nRT/P = (0.14667)(0.08206)( 444)/1.4289 = 3.74 L

 

Question 3

What are the units of pressure of gas b? You need to give me the units of pressure before I can explain you how to answer the question.

 

Question 4

Again make a list of what values are given to you.

T_1 = 73 + 273 = 346 K            T_2 = ?

V_1 = 4.35 L                             V_2 = 3.89 L

The pressure in this question is constant so whe you look at the ideal gas law

PV = nRT you can simplify it to give V/T = k where k a proportionality constant is equal to nR/P. This expression allows you to write the following

V_1/T_1 = V_2/T_2

T_2 = V_2*T_1/V_1 = (3.89)(346)/4.35 = 309 K = 36 degrees

 

Hopefully this answers your problems. Don't be scared of making a list of which are the known and unknown values. Doing this will help you so you won't get overwhelmed. Also don't memorize Boyle's, Charles' and Avagadro's laws. All you need to remember is the ideal gas law as all these laws can be easily derived from it. If you're still confused I suggest that you select a handful of questions from your textbook and try to answer them. The more you practice the easier it will become. 

 

Also please give me the units of pressure of gas b in question 3. Before asking me try to do it on your own now that I've showed how to answer questions 1,2 and 4.