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# Parts Per Million question!!! help really needed!! watch

1. A halogenoalkane, bromomethane, CH3Br, is a toxic gas used to protect plants against insects.

Health and Safety advice states that concentrations above 5 parts per million (ppm) by volume of this gas are harmful.

A research laboratory contains 2.5 × 105 dm3 of air. Calculate the maximum volume of bromomethane, in dm3, allowed in the laboratory to comply with the advice given.

Thanks.
2. (Original post by malteser12345)
A halogenoalkane, bromomethane, CH3Br, is a toxic gas used to protect plants against insects.

Health and Safety advice states that concentrations above 5 parts per million (ppm) by volume of this gas are harmful.

A research laboratory contains 2.5 × 105 dm3 of air. Calculate the maximum volume of bromomethane, in dm3, allowed in the laboratory to comply with the advice given.

Thnaks.
Say you had a million dm^3 of air in the lab. The maximum permissible volume would be 5dm^3. Can you scale down from there?
3. well ppm is usually the percentage x 10000, as the percentage is out of 100 and 100 x 10000 gives 1000000 (a million) so if you work backwards you are given the ppm of 5 therefore 5/10000 = 0.0005% is the amount and you have the amount of air in the room so its just 0.0005% of that
4. (Original post by teeth1234)
well ppm is usually the percentage x 10000, as the percentage is out of 100 and 100 x 10000 gives 1000000 (a million) so if you work backwards you are given the ppm of 5 therefore 5/10000 = 0.0005% is the amount and you have the amount of air in the room so its just 0.0005% of that
Thanks for the help! I think i get it now.
5. (Original post by teeth1234)
well ppm is usually the percentage x 10000, as the percentage is out of 100 and 100 x 10000 gives 1000000 (a million) so if you work backwards you are given the ppm of 5 therefore 5/10000 = 0.0005% is the amount and you have the amount of air in the room so its just 0.0005% of that
That's a better way than the way I do it, ignore me
6. (Original post by Revd. Mike)
That's a better way than the way I do it, ignore me
lol, i think it still gives the same answer i was taught the way you said but found it too long so thought of this way my chem teacher doesnt like it tho for some reason and insists on teaching the other way haha
7. (Original post by malteser12345)
Thanks for the help! I think i get it now.

are u sitting salters unit 2 again today?

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