Question

calculate the molality of a solution formed by adding 9.40 g nh₄cl to 12.8 g of water.
molality: m nh₄cl
tools
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Explanation:

Step1: Calculate moles of NH₄Cl

The molar mass of NH₄Cl is $M_{NH_4Cl}=(14 + 4\times1+35.5)\ g/mol = 53.5\ g/mol$. The number of moles of NH₄Cl, $n=\frac{m}{M}$, where $m = 9.40\ g$. So $n=\frac{9.40\ g}{53.5\ g/mol}=0.176\ mol$.

Step2: Convert mass of water to kg

The mass of water is $m_{water}=12.8\ g = 0.0128\ kg$.

Step3: Calculate molality

Molality ($m$) is defined as the number of moles of solute per kilogram of solvent. So $m=\frac{n}{m_{water}}=\frac{0.176\ mol}{0.0128\ kg}=13.75\ m$.

Answer:

$13.75\ m$