How much water must be added to 12 grams of a 90% iodine solution to produce a 25% iodine solution?

Question

3914 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-08-24T23:46:45

You would have to add 31.2 g of water.

Iodine dissolves in water only to 0.03 % concentration, so this is a purely hypothetical question.

90 % iodine means $"90 g iodine"/"100 g solution"$

So in 12 g of 90 % solution:

$"Mass of iodine" = 12 color(red)(cancel(color(black)("g soln"))) × "90 g iodine"/(100 color(red)(cancel(color(black)("g soln")))) = "10.8 g iodine"$

We add $x " g"$ of water to $"12 g"$ of 90 % iodine to get $12+x " g"$ of 25 % iodine.

$10.8/(12+x) = 25/100$

$10.8×100=25(12+x)$

$1080=300+25x$

$25x = 1080-300 = 780$

$x = 780/25$

$x = 31.2$

We have to add 31.2 g of water.

Check:

$10.8/(12+31.2) = 25/100$

$10.8/43.2 = 25/100$

$1/4=1/4$

It checks!