Question

Question #b082f

Answer 1

You must add 80 g of `"CaCl"_2·6"H"_2"O"`.

Explanation:

Step 1. Calculate the masses of `"Na"_2"CO"_3` and of water in the solution

`"Mass of soln" = 47 color(red)(cancel(color(black)("mL solution"))) × "1.08 g solution"/(1 color(red)(cancel(color(black)("mL solution")))) = "50.8 g solution"`

`"Mass of Na"_2"CO"_3 = 50.8 color(red)(cancel(color(black)("g solution"))) × ("25 g Na"_2"CO"_3)/(100 color(red)(cancel(color(black)("g solution")))) = "12.7 g Na"_2"CO"_3`

Step 2 Calculate the mass of `"CaCl"_2·6"H"_2"O"` to be added

Let `x = "mass of CaCl"_2·6"H"_2"O"`. Then

`"Total mass" = (47 + x)color(white)(l)"g"`

`12.7/(47 + x) = 0.10`

`12.7 = 0.10(47 + x) = 4.7 + 0.10x`

`0.10x = 8.0`

`x = 8.0/0.10 = "80 g"`

You must add 80 g of `"CaCl"_2·6"H"_2"O"` to the solution.