A solution is prepared by dissolving 10.0 g NaCl in 600 g of water. What is its molality? (Note: the molar masses are NaCl = 58.5 g/mol; H2O = 18.0 g/mol)
A.
0.892m NaCl
B.
0.285m NaCl
C.
5.13m NaCl
D.
1.81m NaCl

Option B. 0.285m NaCl

Explanation:

To find the molality, first let find the number of mole of NaCl in the solution. This is illustrated below

Molar Mass of NaCl = 58.5 g/mol

Mass of NaCl = 10g

Number of mole of NaCl = Mass of NaCl / molar Mass of NaCl

Number of mole of NaCl = 10/58.5 = 0.1709mol

Mass of water = 600g = 600/1000 = 0.6kg

Molality = mole of solute / mass of solvent

Molality = 0.1709mol/0.6kg

Molality = 0.285mol/Kg