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A-Level Biology Dilution Question

Hey,

So I'm just doing some revision and I don't get how to work out the answer to the question below.
dilution.PNG

I tried converting 1 g dm-3 to 0.001 g cm-3 and 1ppt to 1000ppm (but I really don't think that was necessary lol).

I'd really appreciate any guidance. Thanks.
(edited 3 years ago)
I'm not sure if I'm right what did you get - i got 0.04cm3 and 39.96 cm3 of water.
Where did you get this question from? (good qs)
Original post by replaythat
I'm not sure if I'm right what did you get - i got 0.04cm3 and 39.96 cm3 of water.
Where did you get this question from? (good qs)

Hey. My teacher gave us the question and we marked it in class today but I don't get it (and I didn't say :P )
The answer is 0.4 and 39.6.
The method you used to get 39.96 (40 - 0.04, I'm assuming) is the same method used to get 39.6 (40 - 0.4 = 39.6) but I don't know how to get to the 0.4
Basically i used the formula C1V1 = C2V2
C1 = Total concentration of the solution = 1 ppt
V1 = Total volume of the solution = 40cm3
C2 = Concentration of the added solution = 10ppm (since they are in different units we need to convert) so i converted to ppt by doing (10/1000) = 0.01
V2 = Volume of stock solution and his is what your trying to find out
So then you rearrange the formula (C1×V1)÷C2 =V2
Therefore (0.01×40)/10 = 0.04 cm3 this is the volume in the stock solution
To find out how much water there is you always take the total volume away from the volume in the stock solution

Hope this helps xx
Original post by replaythat
Basically i used the formula C1V1 = C2V2
C1 = Total concentration of the solution = 1 ppt
V1 = Total volume of the solution = 40cm3
C2 = Concentration of the added solution = 10ppm (since they are in different units we need to convert) so i converted to ppt by doing (10/1000) = 0.01
V2 = Volume of stock solution and his is what your trying to find out
So then you rearrange the formula (C1×V1)÷C2 =V2
Therefore (0.01×40)/10 = 0.04 cm3 this is the volume in the stock solution
To find out how much water there is you always take the total volume away from the volume in the stock solution

Hope this helps xx


Got it!
C1 = 10 ppm
V1 = 40cm³
C2 = 1 ppt = 1000 ppm
V2 = ?

V2 = (C1 × V1) ÷ C2 = (10 × 40) ÷ 1000 = 400 ÷ 1000 = 0.4cm³

So volume of water added = 40cm³ - 0.4cm³ = 39.6 cm³
Original post by SapphirePhoenix1
Got it!
C1 = 10 ppm
V1 = 40cm³
C2 = 1 ppt = 1000 ppm
V2 = ?

V2 = (C1 × V1) ÷ C2 = (10 × 40) ÷ 1000 = 400 ÷ 1000 = 0.4cm³

So volume of water added = 40cm³ - 0.4cm³ = 39.6 cm³

yup exactly
Original post by SapphirePhoenix1
Got it!
C1 = 10 ppm
V1 = 40cm³
C2 = 1 ppt = 1000 ppm
V2 = ?

V2 = (C1 × V1) ÷ C2 = (10 × 40) ÷ 1000 = 400 ÷ 1000 = 0.4cm³

So volume of water added = 40cm³ - 0.4cm³ = 39.6 cm³

Do you by any chance know which exam board this qs is from?
Original post by replaythat
Do you by any chance know which exam board this qs is from?


AQA maybe? Since that's my exam board.

Then again, my bio teacher likes to use questions from other exam boards too :/
Original post by SapphirePhoenix1
AQA maybe? Since that's my exam board.

Then again, my bio teacher likes to use questions from other exam boards too :/

Ahhh thanks much appreciated xx
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Avatar for spsb123
spsb123
10
Original post by replaythat
Do you by any chance know which exam board this qs is from?

AQA 2019 Biology Paper 2 - Not available online yet
Original post by spsb123
AQA 2019 Biology Paper 2 - Not available online yet

Ahhh thanks so much we only did half of that paper

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