Calculate the number of moles of solute present in each of...

Calculate the number of moles of solute present in each of the following solutions: (a) $255 \mathrm{~mL}$ of $1.50 \mathrm{M} \mathrm{HNO}_{3}(a q),(\mathbf{b})$ $50.0 \mathrm{mg}$ of an aqueous solution that is $1.50 \mathrm{~m} \mathrm{NaCl}$, (c) $75.0 \mathrm{~g}$ of an aqueous solution that is $1.50 \%$ sucrose $\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)$ by mass.

Calculate the number of moles of solute present in each of the following solutions: (a) $255 \mathrm{~mL}$ of $1.50 \mathrm{M} \mathrm{HNO}_{3}(a q),(\mathbf{b})$ $50.0 \mathrm{mg}$ of an aqueous solution that is $1.50 \mathrm{~m} \mathrm{NaCl}$,
(c) $75.0 \mathrm{~g}$ of an aqueous solution that is $1.50 \%$ sucrose $\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)$ by mass.

Key Concepts

Mole Concept

The mole concept is a central idea in chemistry that relates the mass of a substance to its number of particles using Avogadro's number. It provides a bridge between the atomic scale and the macroscopic scale, allowing chemists to count entities by weighing them. In solution chemistry, knowing the number of moles of solute helps in understanding reactivity and constructing balanced equations.

Percent Composition by Mass

Percent composition by mass, or mass percent, indicates the mass of the solute present in 100 grams of solution. It is a way of expressing how much solute is in a mixture relative to the total mass of the solution. To find the number of moles of solute, the mass percent is used along with the total mass of the solution and the molar mass of the solute.

Unit Conversion

Accurate unit conversion is essential in solution calculations. Common conversions include converting milliliters to liters and milligrams to grams or kilograms. These conversions ensure that the concentrations (such as molarity and molality) are used correctly in calculations, maintaining consistency in the units used.

Molarity

Molarity is defined as the number of moles of solute dissolved per liter of solution. It is a fundamental concentration unit used to determine how many moles of a substance are present in a given volume of solution. When given a solution's volume and its molarity, the number of moles of solute can be calculated by multiplying the volume (in liters) by the molarity.

Molality

Molality measures the concentration of a solution in terms of moles of solute per kilogram of solvent. Unlike molarity, which depends on the total volume of the solution, molality depends solely on the mass of the solvent. This unit is particularly useful when temperature variations are involved since mass remains constant with temperature changes.

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