Chapter 14: Solutions

Concentration

The measure of the amount of solute dissolved in a given amount of solvent or solution.

Percent by Mass

The mass of solute divided by the total mass of the solution, multiplied by 100%.

Percent by Volume

The volume of solute divided by the total volume of the solution, multiplied by 100%.

Molarity (M)

The number of moles of solute per liter of solution (mol/L).

Molality (m)

The number of moles of solute per kilogram of solvent (mol/kg).

Concentration Units

• Percent by Mass: Often used in industrial and food chemistry.
• Percent by Volume: Common for liquid-liquid solutions like alcoholic beverages.
• Molarity: Convenient for reactions in aqueous solutions.
• Molality: Used in calculations involving temperature changes (e.g., freezing point depression).

Calculating Concentrations

Percent by Mass Formula

$\left(\frac{\mathrm{mass of solute}}{\mathrm{mass of solution}}\right)\times 100\%$

Percent by Volume Formula

$\left(\frac{\mathrm{volume of solute}}{\mathrm{volume of solution}}\right)\times 100\%$

Molarity Formula

$M=\frac{\mathrm{moles of solute}}{\mathrm{liters of solution}}$

Molality Formula

$m=\frac{\mathrm{moles of solute}}{\mathrm{kilograms of solvent}}$

Applications of Concentration

• Titration: Determines the concentration of an unknown solution using a solution of known concentration.
• Colligative Properties: Properties like boiling point elevation and freezing point depression depend on the concentration of solute particles.
• Industrial Processes: Precise concentrations are critical in chemical manufacturing and pharmaceuticals.

Questions for Students

1. Define molarity and molality. What are their units?
2. Write the formula for calculating percent by mass and explain each term.
3. Why is molality used in temperature-related calculations?
4. What is the difference between percent by volume and percent by mass?
5. How does concentration affect colligative properties?