Question

Calculate the molality of a solution containing 14. 3 g of nacl in 42. 2 g of water

Answer 1

Answer:

5.80 M

Explanation:

In this problem, the solute is NaCl and the solvent is water. To find the molality, you need to (1) convert grams NaCl to moles NaCl (via molar mass), then (2) convert grams H₂O to kilograms H₂O, and then (3) calculate the molality (via molality equation). The final answer should have 3 sig figs to match the sig figs of the given values.

(Step 1)

Molar Mass (NaCl): 22.990 g/mol + 35.453 g/mol

Molar Mass (NaCl): 58.443 g/mol

14.3 grams NaCl                1 mole
--------------------------  x  ------------------------  =  0.245 moles NaCl
                                     58.443 grams

(Step 2)

1,000 g = 1 kg

42.2 grams H₂O                 1 kg
--------------------------  x  -----------------------  =  0.0422 kg H₂O
                                      1,000 grams

(Step 3)

Molality = moles solute / mass solvent (kg)

Molality = 0.245 moles NaCl / 0.0422 kg H₂O

Molality = 5.80 M