# Dilutions!Watch

#1
Although this will probaly seem like I'm stupid...
...I can't work out what factor I need to multiply my final value for to work back througha series of dilutions - I'll try to explain.

I start off with an iron tablet. I dissolve it a 250ml flask wihich is made up to the mark with distilled water. I then take 5ml of this solution and add it to a 100ml flask. Thsi flask is made up to the mark. I then take 10ml from the 100ml flask and use it for colorimetric analysis. After comparing the absorbance to a graph for the iron ions I have a concentration of - lets say for simplicity - 0.1mol/l. Using n =c*v, with c as 0.1 mol/l and v as 0.01l (10ml).
This means n =0.001 for my 10ml solution.
What factor do I multiply n by to get the number of moles of Fe in original tablet?

Any help v.much appreciated
0
9 years ago
#2
(Original post by dogjam91)
Although this will probaly seem like I'm stupid...
...I can't work out what factor I need to multiply my final value for to work back througha series of dilutions - I'll try to explain.

I start off with an iron tablet. I dissolve it a 250ml flask wihich is made up to the mark with distilled water. I then take 5ml of this solution and add it to a 100ml flask. Thsi flask is made up to the mark. I then take 10ml from the 100ml flask and use it for colorimetric analysis. After comparing the absorbance to a graph for the iron ions I have a concentration of - lets say for simplicity - 0.1mol/l. Using n =c*v, with c as 0.1 mol/l and v as 0.01l (10ml).
This means n =0.001 for my 10ml solution.
What factor do I multiply n by to get the number of moles of Fe in original tablet?

Any help v.much appreciated
What you react was the number of moles of Fe in that 10 ml of further diluted original solution, so you need to multiply by 10 to get the total number of moles in the 100ml. However, this 100 ml is further diluted 20 times from 5 ml, so you need to multiply further by 20 to get true number of moles of Fe in that 5 ml, then to get the total in the 250ml(diluted by 50 times), multiply by 50,

in total, multiply by 10 x 20 x 50 = 10^4

Think that should be right.
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