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Calculate the molality of a 45.3% by mass KBr solution.

Question:

Calculate the molality of a 45.3% by mass KBr solution.

Molality:

The term molality indicates the molar concentration of a solute in a solution. This is obtained from the ratio of the number of moles of solute and the mass of the solution. Molarity involves the concentration of the solution in terms of the volume of solution.

Answer and Explanation: 1

Given data:

  • Mass percentage of KBr is 45.3 %.

We have to find the molarity.


If the total mass of solution is 100 g, we get the mass of KBr is 45.3 g, and the mass of water is 54.7 g.

We have molar mass of KBr as 119.00 g/mol.


Molality is obtained as shown below,

{eq}\rm \begin{align*} \rm molality &= \rm \dfrac{{mass\,(g) \times 1000}}{{molar\,mass \times mass\,of\,solvent\,\left( g \right)}}\\ &= \rm \dfrac{{45.3\;g \times 1000}}{{119.00\;g/mol \times 54.7\;g}}\\ &= \rm 6.96\;m \end{align*} {/eq}


Thus, molality is 6.96 m.


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