Im taking 11U chem and my exam is coming up. Ive run into a few problems while ive been studying and I just cant solve them.

Question 1:

Rutherford proved that alpha particles...blah blah random question [censored]...In an experiment 1.806 x 10¹⁷ alpha particles were counted using a Geiger counter. The resulting helium gas occupied a volume of 7.34 x 10^-3 mL at 99.3 kPa and 19^oC (292^oK) Use this information to calculate Avogadro number.

Ive gotten close using the Ideal gas law (PV=NRT) but not close enough. No matter what I do I cant get it to equal 6.02 x 10²³

Question 2:

The total pressure of He and CO is 90.0 kPa. If there is twice as much CO as He what is the partial pressure for both gasses.

I know this one is easy but I haven't done since near the beginning of the year and I cant find my notes on partial pressure.


Thanks

Holy [censored]. Less than a year ago I could have told you exactly what you are looking for.

Now I can't. At all.

Welcome to the education system, my friend. It is a wonderful place where useless information you'll never use or remember will be crammed down your throat.

I'm in the same position as Defaulted on this one.

For the first one, you need to use the ideal gas law, and set it so that n = PV/RT. Make sure you keep note of the terms involved, especially with R, or you will get this incorrect. Once you have n, divide it by the number of alpha particles you have there, and it should be within significant figures to round up to Avogadro's number, depending on how serious you treat significant figures.

For the second one, mass doesn't matter, just the number of molecules. You have 2, CO and He. For every 1 He atom, there are 2 CO molecules. With this knowledge, you can easily find what the partial molar volume is. Using that, calculate the partial pressures of the gasses by plugging in xi = Pi/Pt, where xi is the partial molar volume of a given gave, Pi is the partial pressure of a given gas, and Pt is total pressure.

And no, I will not tell you the answers.

Hellmouth is correct for the first one, thanks for reminding me how to do it.

I'm not familular with the Canadian educational system, so what's 11U to grades in the US? Would that be equivalent to 11th grade to the US (3rd year in high school)?

Thanks a lot, I was able to get the first one actually. Calculator wasn't set correctly :brokencomputer: And yeah that makes sense for number two. SCH 11U is Grade 11 University (Academic) Chemistry, so yes.

well it better be correct, or I have failed miserably as a recent graduate of chemistry at my college.

~ (11U = 11th grade honors course)

12U courses are mandatory to get into a Canadian uni.