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27 November, 20:08

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.

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  1. 27 November, 22:42
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    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
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