Alain12345
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Practice Questions?
I have a test on Monday, and I need to find some questions on the internet for practice. My chemistry textbook has some, but it's not enough. I need
questions related to concentrations of solutions... %V/V, %W/V, %W/W, PPM, PPB, PPT, and molar concentration.
Thanks.
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runlabrun
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google search, there are plenty of universities and schools that put their tests on open access web servers.
-rlr
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The_Davster
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This was the third google result, I believe it is what you are looking for, most of the sites that came up with the google search will provide better
practice questions than we could.
http://www.oaklandcc.edu/iic/iicah/ah_www_che_sol.htm
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12AX7
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Come up with your own. 
May not get the convienient rounded answers the carefully crafted textbook Q's get, but identifying and creating problems is as instructive as solving
them.
Tim
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Alain12345
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| Quote: | Originally posted by rogue chemist
This was the third google result, I believe it is what you are looking for, most of the sites that came up with the google search will provide better
practice questions than we could.
http://www.oaklandcc.edu/iic/iicah/ah_www_che_sol.htm |
Thanks for the link, but I need help with something. There are a lot of questions that have "M". I don't know what that is.
One question says: What volume of 0.86 M table sugar (C12H23O12) has 50 grams of sugar in it?
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The_Davster
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M is just molarity, the lazy way of writing mol/L
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Alain12345
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Oh, okay thanks. There's this one question from my textbook, and it says "If a 500-L indoor air sample with a mass of 0.59 kg contained 3.2 mg of
formaldehyde, this would be considered a dangerous level. What would be the concentration in ppm?"
I know that that answer is 5.4 ppm, but this is because my teacher told me that the 500-L is there to confuse you. How would I know this? PPM
questions can have mass and volume in them, right?
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Darkblade48
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| Quote: | Originally posted by Alain12345
Oh, okay thanks. There's this one question from my textbook, and it says "If a 500-L indoor air sample with a mass of 0.59 kg contained 3.2 mg of
formaldehyde, this would be considered a dangerous level. What would be the concentration in ppm?"
I know that that answer is 5.4 ppm, but this is because my teacher told me that the 500-L is there to confuse you. How would I know this? PPM
questions can have mass and volume in them, right? |
The 500 L isn't there to "confuse" you per se, it's just a piece of information that is not used at all.
I did the following:
Convert 3.2 mg to kg = 3.2 / 1 000 000 and then / 0.59 (mass of air)
This gives us the ratio of formaldehyde to air
which gives us 5.42 * 10^-6 or 5.42 ppm.
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unionised
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ppm for gases usually refers to ppm by volume. In this case about 5.12 ppm
3.2 mg =3.2/30.03 milimoles
each milimole is about 24 mililiters so you have 2.56 ml of formaldehyde in 500 Litres of air
1000000* 2.56/500000 =5.12 ppm
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mick
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I was going to reply to the concentration and molecular weight of sugar.
Another interesting question is, if you work at a university and someone drops a winchester of ether when should you recommend evacuation.
My calculations keep coming up with about 34 cubic meters of easily ignited vapours.
mick
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