Kaplan gen chem question...help dat in 1 week

[hillrei]

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Hey guys i need some help, im going through the gases part of the gen chem section of the kaplan blue book and im having some trouble. I thought i knew how to do these problems easy buy the kaplan answers are really confusing and i cannot figure out what or how there doing these... how would you guys answer these problems:
(CH.7, problems 8,9,12,15 from kaplan blue book)

1. Problem number 8 in kaplan bb: What is the density of a gas at 76 torr and 37 C (MM = 25g/mol)

2. problem number 9 in kaplan bb: H2+Cl2 = 2HCL, what many grams of chlorine gas are needed to produce 3L of HCL at a pressure of 2atm and 19C?

3. Problem 12 from kaplan bb: a 1.74g sample of gas is found to occupy 1 L at 10C and 2 atm What is MM of gas?

4. problem 15 from kaplan bb: N2 + 2O2 = 2 NO2, what volume of NO2 is produced from 7g of ntrogen gas at 27C and .9atm?

Thanks so much for you guys help with this!

 

[tsitneD]

Hey guys i need some help, im going through the gases part of the gen chem section of the kaplan blue book and im having some trouble. I thought i knew how to do these problems easy buy the kaplan answers are really confusing and i cannot figure out what or how there doing these... how would you guys answer these problems:
(CH.7, problems 8,9,12,15 from kaplan blue book)

1. Problem number 8 in kaplan bb: What is the density of a gas at 76 torr and 37 C (MM = 25g/mol)

2. problem number 9 in kaplan bb: H2+Cl2 = 2HCL, what many grams of chlorine gas are needed to produce 3L of HCL at a pressure of 2atm and 19C?

3. Problem 12 from kaplan bb: a 1.74g sample of gas is found to occupy 1 L at 10C and 2 atm What is MM of gas?

4. problem 15 from kaplan bb: N2 + 2O2 = 2 NO2, what volume of NO2 is produced from 7g of ntrogen gas at 27C and .9atm?

Thanks so much for you guys help with this!

1) P(MW)= DRT .... remember this. for sure showing up on test day.

2) use PV=nRT for HCL to get moles then use reaction to find chlorine gas moles. After im sure you can figure out the mass.

3) P(MW) = DRT... again use this rmr Density = Mass/ Vol.

4) Same as question #2

 

[tsitneD]

make sure right units are used

R= .08 or ~.1 then make sure you use pressure in atm, volume in L, temp in Kelvin (T).

Also when it says nitrogen gas. Its N2 so take 28 MW and not 14 MW.

 

[tsitneD]

i did really fast calc with lots of rounding off and the answers are:

1) D~ 1/12
2) 7 grams
3) MW ~ 28
4) V = 15 L

I used my above mentioned method of approach. let me know right or wrong?

 

[nze82]

Hey guys i need some help, im going through the gases part of the gen chem section of the kaplan blue book and im having some trouble. I thought i knew how to do these problems easy buy the kaplan answers are really confusing and i cannot figure out what or how there doing these... how would you guys answer these problems:
(CH.7, problems 8,9,12,15 from kaplan blue book)

1. Problem number 8 in kaplan bb: What is the density of a gas at 76 torr and 37 C (MM = 25g/mol)
1atm = 760torr-->76torr = 0.1atm
K = 37 + 273 = 310K
Density = (MM)P/RT = (25)(0.1)/(0.082)(310) = 0.098

2. problem number 9 in kaplan bb: H2+Cl2 = 2HCL, what many grams of chlorine gas are needed to produce 3L of HCL at a pressure of 2atm and 19C?
Find the # of moles of HCl via the following formula:
PV = nRT--> n = PV/RT = (2)(3)/(0.082)(292) = 0.25 mole of HCl
K = 19 + 273 = 292
Now find the # of moles of Cl2:
0.25mole of HCl x (1mole Cl2)/(2mole HCl) = 0.125 mole Cl2
Finally go ahead and find the # of gr:
0.125mole Cl2 x (71g/1mole Cl2) = 8.9gr of Cl2

3. Problem 12 from kaplan bb: a 1.74g sample of gas is found to occupy 1 L at 10C and 2 atm What is MM of gas?
D = (MM)P/RT
So:
MM = D(RT)/P
D = m/V = (1.74)/(1L) = 1.74 g/L
MM = (1.74)(0.082)(283K)/2 = 20.2g/mole
K = 10 + 273 = 283K

4. problem 15 from kaplan bb: N2 + 2O2 = 2 NO2, what volume of NO2 is produced from 7g of ntrogen gas at 27C and .9atm?
7gr N2 x (1mole N2)/(28g) x (2mole NO2)/(1mole N2) = 0.5mole NO2
PV = nRT
V = nRT/P = (0.5)(0.082)(300)/(0.9) = 13.7L
K = 27 + 273 = 300K

Thanks so much for you guys help with this!

The general solutions are correct. If you see discrepancies in the answers, check the math!

Hope this helped!

 

[tsitneD]

^^ better explained with good calc.

 

[hillrei]

Thanks so much guys. That helps out a ton. I really appreciate it.

 

[anteater85]

The general solutions are correct. If you see discrepancies in the answers, check the math!

Hope this helped!

thi really helped because i was using the Kaplan's method and everytime i was confused where to use the 22.4 for V or when 1 atm is for P1 or P2...thx a lot with the P(mw)=DRT equation 🙂