Chemistery question calculating molality

Question

What is the molality of a solution that contains 2.50 moles of NaCl in 150 mL of water? (The density of water is equal to 1.0  .)

Answer 1

Molality is a way to talk about the concentration of a solution.

Molality is defined as: moles of solute per mass (kg) of solvent

In this case, the solute is NaCl, and we know we have 2.50 moles.

The solvent is water, and we have a volume (150mL) of water but not the mass.

To find this answer we first have to calculate the mass of the water using stoichiometry to get the units we need:

volume (mL) * density (g/mL) = mass (g)

150mL * 1g/mL * 1kg/1000g = 0.150kg of water

Now we can calculate molality:

2.50moles/0.150kg = 16.7moles/kg

All of the values given in this problem have 3 significant figures, so your answer should be given with 3 significant figures as well.

Answer 2

molality is grams of solute peer kg of sovent

2.5 moles NaCl /150 ml H2O x 1ml H2O /1gm H2O x 1000 gm/kg = 16.67 Moles Na Cl / kg H2O