Question

What percent concentration of KCl would be isotonic?

Answer 1

Isotonic with what?

Explanation:

A 1.1 % (m/m) solution of KCl would be isotonic with blood.

Two solutions are isotonic if they have the same osmotic pressure or osmolality.

The normal osmolality of blood is about `"290 mOsmol/kg"` or `"0.29 Osmol/kg"`.

`"KCl" → "K"^+ + "Cl"^-`

∴ `"1 mol KCl" = "2 Osmol"`

`(0.29 color(red)(cancel(color(black)("Osmol"))))/"1 kg" × (1 color(red)(cancel(color(black)("mol KCl"))))/(2 color(red)(cancel(color(black)("Osmol")))) × "74.55 g KCl"/(1 color(red)(cancel(color(black)("mol KCl")))) = "11 g KCl/kg"`

So there are `"11 g KCl"` in `"1000 g H"_2"O"`.

`"% KCl" = (11 color(red)(cancel(color(black)("g"))))/(1011 color(red)(cancel(color(black)("g")))) × "100 %" = "1.1 %"`