[saparama]

The problem is: We have a 20% solution of NaCl and we want to create 3 litres of 1% NaCl solution. Question is how many litres of 20% solution and how many litres of water should we use to create such thing.

It was on my exam and I tried to use c1.V1 = c2.V2    From  equation m1.w1 = m2.w2 i found out that m1 = 0,05.m2  but that is all I got. Can someone please help me? How should I continue? Does this problem have a solution?

[chenbeier]

Use cross rule

20.             1 weight part
          1
0.               19 weight part
______________
                    20 weight part = 3 kg

You need the specific gravity to convert to volume.

If you calculate in mass 3 kg 1% solution  = 20 weight parts

You need 150 g 20% solution ( 1 weight part) and 2,85 kg (19 weight part) of water.

[saparama]

Use cross rule

20.             1 weight part
          1
0.               19 weight part
______________
                    20 weight part = 3 kg

You need the specific gravity to convert to volume.

If you calculate in mass 3 kg 1% solution  = 20 weight parts

You need 150 g 20% solution ( 1 weight part) and 2,85 kg (19 weight part) of water.

Thank you very much for you answer but I have a question. They wanted the answer in volumes. Can I use 0,150 litres and 2,85 litres?

[Borek]

These will be only approximate, density of the 20% NaCl solution is around 1.15 g/mL, so 150 g is quite far from being 150 mL,

If you were not given densities 150 mL is your best bet though.