How do you get a 10 percent solution from a 95 percent solution?

Answer 1

If you mean: % by MASS ( %m/m), it's quite easy to do (based on the 'Mass Conservation Law).

1. Measure 10 gram of the 95%m/m original solution, this contains 95% of 10g = 9.5g Solute
2. Then add new solvent up to 95g final solution, so adding (95g - 10g =) 85 gram new solvent, then you'll get:
3. 9.5g Solute (in 10 g of original solution) in 95g (final) solution, thus 9.5g S / 95g = 10%m/m

However if the meaning was: % by Volume ( %v/v) then calculation appears to get very complicated, but not impossible if you know at least the density values of all solutions (original 95%v/v and final 10%v/v) and of the solvent.

(In that case mail me: JoppeDeQuint at answers dot com).

DO NOT ever use: (orig. volume) + (added volume) = final volume.

It's only a rule of thump, an approximation. This is because fluids can contract on mixing at dilution. There is no rule such as: conservation of volume.

Your case: 10 ml + 85 ml (is not equal but) < 95 ml final solution.