SOLUTION: Given a stock solution of 5.0% sodium chloride (NaCl), how would you prepare 20 ml of a 2.0% sodium chloride solution? (I have tried many of the examples you give others but I can'

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Question 498280: Given a stock solution of 5.0% sodium chloride (NaCl), how would you prepare 20 ml of a 2.0% sodium chloride solution? (I have tried many of the examples you give others but I can't work it out for some reason.)
Answer by josmiceli(19441) (Show Source):
You can put this solution on YOUR website!
In words:
(ml of NaCl you end up with) / (ml of total solution you end up with) = 2%
They are not telling you how many ml of the stock solution you start with.
They only say you end up with 20 ml of solution.
In order to get down from 5% to 2% you must add water ( or whatever the solvent is)
They should have mentioned that
Let = ml of the 5% solution you need
Let = ml of water to add
given:
= NaCl in the 5% solution
(1)
---------------
(2)
(2)
(2)
and, since
(1)
(1)
(1)
You need 8 ml of the 5% solution
and 12 ml of water
check:
(2)
(2)
(2)
(2)
OK