In the lab, a student adds 4.5 g of sodium chloride (NaCl) to 100.0 g of water. Calculate the molality of the solution.

0.77mol/Kg.

Explanation:

The following data were obtained from the question:

Mass of NaCl = 4.5g

Mass of water = 100g.

Molality = ... ?

Next, we shall determine the number of mole in 4.5g of NaCl. This can be obtained as follow:

Mass of NaCl = 4g.

Molar mass of NaCl = 23 + 35.5 = 58.5g/mol

Number of mole NaCl = ... ?

Mole = Mass / Molar Mass

Number of mole of NaCl = 4.5/58.5

Number of mole of NaCl = 0.077 mole.

Next, we shall convert 100g of water to kilograms. This is illustrated below:

1000g = 1kg

Therefore, 100g = 100/1000 = 0.1Kg.

Finally, we can determine the molality of the solution as follow:

Molality is simply defined as the mole of solute per unit kilogram of solvent (water). Mathematically, it is represented as:

Molarity = mole of solute / kg of solvent

Mole of solute, NaCl = 0.077 mole

Kg of solvent = 0.1kg

Molality = 0.077mol/0.1kg

Molality = 0.77mol/Kg