Question

question 20 (5 points)
whats the molality of a solution with 120 g of nacl and 30 kg of water?
a) 6.8
b) 0.004
c) 0.25
d) 0.068

Explanation:

Step1: Calculate moles of NaCl

Molar mass of NaCl: $Na = 23\ g/mol$, $Cl = 35.5\ g/mol$, so molar mass of NaCl is $23 + 35.5 = 58.5\ g/mol$.
Moles of NaCl = $\frac{mass\ of\ NaCl}{molar\ mass\ of\ NaCl} = \frac{120\ g}{58.5\ g/mol} \approx 2.051\ mol$.

Step2: Convert mass of water to kg (already in kg: 30 kg)

Molality ($m$) is defined as moles of solute per kilogram of solvent.

Step3: Calculate molality

$m = \frac{moles\ of\ solute}{kg\ of\ solvent} = \frac{2.051\ mol}{30\ kg} \approx 0.068\ mol/kg$.

Answer:

D) 0.068