What is the molality of phosphoric acid, H3 PO4, in a...

What is the molality of phosphoric acid, $\mathrm{H}_{3} \mathrm{PO}_{4}$, in a solution of $14.5 \mathrm{g}$ of $\mathrm{H}_{3} \mathrm{PO}_{4}$ in $125 \mathrm{g}$ of water? (a) Outline the steps necessary to answer the question. (b) Answer the question. 37. What is the molality of nitric acid in a concentrated solution of nitric acid ( $68.0 \%$ HNO $_{3}$ by mass)? (a) Outline the steps necessary to answer the question. (b) Answer the question.

What is the molality of phosphoric acid, $\mathrm{H}_{3} \mathrm{PO}_{4}$, in a solution of $14.5 \mathrm{g}$ of $\mathrm{H}_{3} \mathrm{PO}_{4}$ in $125 \mathrm{g}$ of water?
(a) Outline the steps necessary to answer the question.
(b) Answer the question.
37. What is the molality of nitric acid in a concentrated solution of nitric acid ( $68.0 \%$ HNO $_{3}$ by mass)?
(a) Outline the steps necessary to answer the question.
(b) Answer the question.

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Key Concepts

Mass Percent Composition

Percent composition by mass is a way of expressing the concentration of a component in a mixture, defined as the mass of the component divided by the total mass of the solution, multiplied by 100. This concept is critical when dealing with solutions described by percentage composition, as it allows one to deduce the mass of the solute or solvent from the overall mass.

Distinguishing Solvent and Solute Mass

In molality calculations, it is essential to differentiate between the mass of the solute and the mass of the solvent. The calculation relies solely on the mass of the solvent (in kilograms), rather than the total mass of the solution, ensuring that the concentration measurement remains independent of changes in volume.

Molality

Molality is a concentration unit that measures the number of moles of solute per kilogram of solvent. It is especially useful in scenarios where temperature changes occur because mass does not change with temperature, in contrast to volume.

Molar Mass and Mole Calculations

Determining the number of moles of a substance requires knowing its mass and its molar mass. This conversion is fundamental to many concentration calculations, as it translates mass measurements into the chemical amount (moles) necessary for further analysis.

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