Question

What Is the mass of water absorbed by a mixture containing 2 g of `"CaCl"_2` and 2.5 g of `"K"_2"CO"_3`?

Answer 1

The total amount of water absorbed is 2 g.

Explanation:

Calcium chloride and potassium carbonate are hygroscopic — they absorb water from the atmosphere and form hydrates.

In fact, they are so hygroscopic that they dissolve in their own water of hydration (deliquesce).

The equations for their formation are

CaCl₂ + 6H₂O → CaCl₂·6H₂O

K₂CO₃ + 1.5H₂O → K₂CO₃·1.5H₂O

We can calculate the mass of water absorbed by each compound.

From CaCl₂:

`"Mass of water" = 2 cancel("g CaCl₂") × (1 cancel("mol CaCl₂"))/(110.98 cancel("g CaCl₂")) × (6 cancel("mol H₂O"))/(1 cancel("mol CaCl₂")) ×"18.02 g H₂O"/(1 cancel("mol H₂O")) = "2 g H₂O"`

From Na₂CO₃:

`"Mass of water" = 2.5 cancel("g K₂CO₃") × (1 cancel("mol K₂CO₃"))/(138.21 cancel("g K₂CO₃")) × (1.5 cancel("mol H₂O"))/(1 cancel("mol K₂CO₃")) × "18.02 g H₂O"/(1 cancel("mol H₂O")) = "0.49 g H₂O"`

If you have both together, the total mass of water absorbed is

`"(2 + 0.49) g H₂O" = "2 g H₂O"`

Note: The answer can have only one significant figure because that is all you gave for the mass of the CaCl₂.