chem help

[RING12]

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A researcher adds 0.4 kg of CaBr2 (MW=200g/mol) to 10L of water, in which it disolves completely:

How much water would the researcher need to add to the solution in order to decrease the concentration by factor of 4?😱

 

[wizi]

A researcher adds 0.4 kg of CaBr2 (MW=200g/mol) to 10L of water, in which it disolves completely:

How much water would the researcher need to add to the solution in order to decrease the concentration by factor of 4?😱

lol Lets me try...

1st: lets define some variables.

x: amount of water we are looking for.
C2= new molality.
C1 = old molality.
--> C2 = C1/4

2nd: Find C1

C1 = mole (CaBr2)/ kg of water
mole of CaBr2 = 400/200 = 2 moles.
kg of water = 10kg (water has density of 1 --> Litter = kg)
--> C1 = 2/10 = 0.2

3rd: Find C2

C2= C1/4 = 0.2/4 = 0.05

4th: Find x

C2 = mole (CaBr2)/ x(kg) --> x (kg) = C2 / mole (CaBr2) = 0.05 / 2 = 0.025 (kg) = 25 (g)

Answer: 25 (g)

Is it right?

 

[jkb53433]

whats the answer? im getting 30L but i dunno if im on the right track

 

[qkchen]

whats the answer? im getting 30L but i dunno if im on the right track

i got 30 ml of water to add, as well, with V2 = 40 ml

 

[RING12]

the right answer is 30L. thanks every one