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Alain12345
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[*] posted on 8-12-2005 at 13:36
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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[*] posted on 8-12-2005 at 14:40


google search, there are plenty of universities and schools that put their tests on open access web servers.

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The_Davster
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[*] posted on 8-12-2005 at 15:23


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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[*] posted on 8-12-2005 at 19:18


Come up with your own. :P

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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[*] posted on 9-12-2005 at 11:25


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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[*] posted on 9-12-2005 at 11:29


M is just molarity, the lazy way of writing mol/L:P



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Alain12345
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[*] posted on 9-12-2005 at 11:52


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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[*] posted on 9-12-2005 at 14:10


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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[*] posted on 10-12-2005 at 13:56


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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[*] posted on 12-12-2005 at 16:28


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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