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# concentration of a substance helpp! Watch

1. hi all, hope you're all having a nice easter holiday! im not ha, doing chemistry coursework.

anyway! I'm quite stuck on how to work out the concentration of a solution that I've diluted.
the substance i'm using is potassium peroxodisulphate of concentration 0.040moldm^-3.

the concentration of 25cm^3 potassium peroxodisulfate with no water would be 0.040moldm^-3.
but what if I diluted it, say 23cm^3 of p.p with 2cm^3 of water, how would I work out the concentration?

thanks for your help!
2. Concentration = moles * volume

Just put in the new volume

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3. (Original post by alexandraa)
Concentration = moles * volume

Just put in the new volume

This was posted from The Student Room's iPhone/iPad App
hey thanks for the reply!
moles? moles of p.p??
4. (Original post by calmpeach)
hey thanks for the reply!
moles? moles of p.p??
Yes you just use the original moles of the p.p.

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5. (Original post by alexandraa)
Yes you just use the original moles of the p.p.

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alright, so the original moles of p.p in 25cm^3 is: 0.040 * 25/1000 = 0.001

then multiply that by the new volume, 23, 0.001x23 = 0.023moldm^-3

is that right??
6. (Original post by calmpeach)
hi all, hope you're all having a nice easter holiday! im not ha, doing chemistry coursework.

anyway! I'm quite stuck on how to work out the concentration of a solution that I've diluted.
the substance i'm using is potassium peroxodisulphate of concentration 0.040moldm^-3.

the concentration of 25cm^3 potassium peroxodisulfate with no water would be 0.040moldm^-3.
but what if I diluted it, say 23cm^3 of p.p with 2cm^3 of water, how would I work out the concentration?

thanks for your help!
Conc = moles * volume

0.04 = 25/1000 * m

Moles in 25 cm 3 is 1.6

1.6/25 is 0.064 moles in every cm3

So there would be 1.472 moles in 23 cm3

Conc = moles * volume
= 1.472 * 23/1000
0.0339 Moldm-3

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7. Oo I see! Thanks a lot!!

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