Question

A solution is made up by dissolving 14.8 g Na2CO3 · 10 H2O in 110.5 g of water. What is the molality of Na2CO3 in this solution?

Answer 1

moles Na2CO3.10H2O = grams/molar mass.
Solve for moles.

Then m = moles/kg solvent
solve for m.

Answer 2

Step 1 - molar mass Na2CO3 = 106 g/mol
Step 2 - molar mass Na2CO3 *10 H2O = 106 + ( 18 x 10) = 286 g/mol

Step 3 - moles Na2CO3*10H2O = 14.8 / 286 = 0.0517
Step 4 - moles water = 10 x 0.0517 = 0.517

Step 5 - mass water = 18 x 0.517 = 9.31 g
Step 6 - Total mass water = 110 + 9.31 = 119.31 g

Step 7 - m = 0.0517 / 0.11931 Kg = 0.433