[NepisManXem]

Hi all,
I have a problem on how to calculate a solution of some substances. How many liters of water needs to be added in a 30% solution of some substances to get 20% solution of the same substances in 100l of water.

thanks in advance

[Borek]

Dilution is basically based on the mass conservation - start by calculation how much substance will be in the final solution, then find out what volume of the starting solution is necessary to supply this amount.

For highly concentrated solutions (and at 20% and 30% you are in this range) this will be impossible without knowing the solution density.

[NepisManXem]

I understand what you said but I need to make a dilution of tomato sauce for making sardines. Of 100 liters of 30% tomato sauce solution to make 20% tomato sauce solution. How much water do I need to add in 30% solution to make 20% solution of tomato sauce? But I'm not sure if I need to know the density of tomato sauce for that calculation.

[chenbeier]

Mixing Cross by weight.
Take 20 parts of the 30 percentage and Mix it with 10 parts of Water. The result is 30 parts of 20%.

[Vidya]

Truly as Borek said it works on  mass conservation.
Based on that we have one dilution law in terms of molarity and same can be modified for percentage also
according it
 30% X100L = 20% X Volume of diluted solution
V = 30 x100/20 = 150L
so you need to add 50L of water to make 30% to 20%