Question

Partial Pressure question

A student collected 98.3 mL of hydrogen gas at 21 C and 798 torr over water. What mass of zinc did they start with? (vapor pressure of water at 21 C=18.7 torr)

Zn(s)+2HCL(aq)--->H2(g)+ZnCl2(aq)
I need to find the partial pressure of hydrogen, then the number of moles of hydrogen, and lastly the mass of zinc. But I have no idea where to start.

Answer 1

I don't think I can help.. Sorry!! I really wish I could... it may be awhile before you get a reply.. not a lot of people help in Chemistry... sorry! :/

Answer 2

I'll try... hmm it's been awhile since I've done stuff like that.

Answer 3

Dalton's Law of Partial Pressure states the total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of each individual gas.

The total pressure of a mixture of gases can be defined as the sum of the pressures of each individual gas: Ptotal=P1+P2+...+Pn .

The partial pressure of an individual gas is equal to the total pressure multiplied by the mole fraction of that gas.

do you understand that part?

Answer 4

Yes I get that part, just confused about which numbers to use

Answer 5

does that mean I add 798 torr and 18.7 torr?

Answer 6

okay... I'm more accustomed to working with Kelvin and atm.. is that okay? or do you need to stay in Celsius and torr? and hang on.. let me read it one more time.

Answer 7

yes, that's fine with me.

Answer 8

okay.. well hang on. I may be able to do it in torr and C

Answer 9

The mole fraction is a way of expressing the relative proportion of one particular gas within a mixture of gases. We do this by dividing the number of moles of a particular gas i by the total number of moles in the mixture:

xi=number of moles i/total number moles of gas

you need to find the mole fraction first.

Answer 10

The partial pressure of one individual gas within the overall mixtures, pi, can be expressed as follows:

Pi=Ptotalxi

where xi is the mole fraction.

then you can find the partial pressure

Answer 11

still having trouble finding moles, would it look something like 1 mole/something grams?

Answer 12

what do you mean you're having trouble finding moles? the amount moles are the coefficients in your chemical equation.

Answer 13

\[1mol H^2/2mole \times 798 torr\] How about this? Cause I need to find the partial pressure of hydrogen. Also sorry that it takes me a while to type. This website glitches a whole lot.

Answer 14

I know it does XD

Answer 15

I'm glad its not just me, lol

Answer 16

I'm thinking. sorry it's taking so long

Answer 17

so, what I said earlier was really confusing.. maybe this can help better... um, look at this and tell me if you still need help. I'm sorry :/ https://www.chem.wisc.edu/deptfiles/genchem/sstutorial/Text9/Tx96/tx96.html