[plesli]

somebody please help me with this problems:

1. At constant T and n, the pressure on 52.9L of a gas is reduced from 792 torr to 761 torr. what is the new volume?

2. How many ML of a 0.386M KF solution contain 0.234 moles of the solute?

Thank you.

by the way, I did try to do the problem by I can't get it.

for problem #1 I was using formula PV=nRT but I wasn't sure.

for problem #2 0.234moles(1L/0.386moles)(1000ML/1L) this is what I did but I wasn't sure either. Please help. Thank you.

[Borek]

for problem #1 I was using formula PV=nRT but I wasn't sure.

Good starting point, try harder

Note that the same equation can be expressed as V/T=const.

for problem #2 0.234moles(1L/0.386moles)(1000ML/1L) this is what I did but I wasn't sure either.

Seems OK. I just can't see result...

[Skyline]

1. At constant T and n, the pressure on 52.9L of a gas is reduced from 792 torr to 761 torr. what is the new volume?

For the 1st question:
you are correct on the PV=nrT equation
since T and n are held constand and r is a constant itself
now you should consider the variables in the equation: V and P

what are the relationship between V and P??
they are inversely related, meaning as pressure increases, volume decreases
with this information, we can predict that the new volume will be larger.  Do you agree??  

so i set up the equation:
P1V1=P2V2

P1= 792 torr
P2= 761 torr
V1=52.9 L
and we'll let x = V2

so plugging in the #s
we get: x = (52.9L)(792 torr)/(761torr)
and x = 55.1 L

I hope this is making sense to you~~

for Question #2

2. How many ML of a 0.386M KF solution contain 0.234 moles of the solute?

Good Job~!
I agree on the way you work out the problem  

Here is another way that you can work this problem
I applied simliar concept
by saying that we have a 0.386M of solution basically means that we have 0.386mole of KF in 1 liter of solution.  Agree??

the amount of solute should be proportional throughout the soultion
therefore i set up this proportion:
let x be the amount of solute that we are looking for
(0.386 mole)/(1000ml) = (0.234 mole) / (x ml)
by sloving this equation,
i found out that x = 606.2mL
which is the same answer as you got, just a different approach.

I hope you found my explainations are somewhat helpful