Solutions: Properties, Calculations, and Applications (Ch. 13 Study Guide)

Solutions in Chemistry

Definition and Types of Solutions

Solutions are homogeneous mixtures composed of two or more substances. The substance present in the largest amount is called the solvent, while the other substances are solutes. Solutions can exist in various phases, such as solid, liquid, or gas.

• Solid solution: Example: Steel (an alloy of iron and carbon).

• Aqueous solution: Water is the solvent.

• Electrolyte solution: Contains ions and conducts electricity.

• Nonelectrolyte solution: Does not conduct electricity; solute does not dissociate into ions.

Example: Salt water is a strong electrolyte solution; sugar water is a weak or nonelectrolyte solution.

Components of a Solution

• Solvent: The major component of a solution.

• Solute: The minor component, dissolved in the solvent.

Additional info: Ionic solutes typically dissolve in polar solvents like water due to ion-dipole interactions.

Concentration Units

Mass Percent

Mass percent expresses the concentration of a solute in a solution as a percentage of the total mass.

• Formula: $\text{Mass percent} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100\%$

• Example: Dissolving 2.45 g of sugar in 200.0 g water: $\text{Mass percent} = \frac{2.45}{202.45} \times 100\% = 1.21\%$

Molarity (M)

Molarity is the number of moles of solute per liter of solution.

• Formula: $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

• Example: Dissolving 15.0 g NaCl in 1.000 L water: Moles NaCl = $\frac{15.0\,g}{58.44\,g/mol} = 0.257\,mol$ Molarity = $\frac{0.257\,mol}{1.000\,L} = 0.257\,M$

Calculating Moles from Mass Percent

• Given mass percent and total mass, calculate mass of solute, then convert to moles using molar mass.

• Example: 34.2 g of a 45.5% NaCl solution: Mass NaCl = $34.2\,g \times 0.455 = 15.6\,g$ Moles NaCl = $\frac{15.6\,g}{58.44\,g/mol} = 0.267\,mol$

Types of Electrolytes

Strong vs. Weak Electrolytes

Electrolytes are substances that dissociate into ions in solution. Strong electrolytes dissociate completely, while weak electrolytes only partially dissociate.

• Strong electrolytes: NaCl, KBr, CaCl2

• Weak electrolytes: Acetic acid (CH3COOH)

• Nonelectrolytes: Sugar (C12H22O11)

Preparation and Dilution of Solutions

Preparing Solutions of Specific Molarity

• Calculate moles of solute needed: $\text{moles} = M \times V$

• Convert moles to grams using molar mass.

• Example: To prepare 50.0 mL of 2.45 M KCl: Moles KCl = $2.45\,mol/L \times 0.050\,L = 0.123\,mol$ Mass KCl = $0.123\,mol \times 74.55\,g/mol = 9.17\,g$

Dilution Calculations

To dilute a stock solution to a lower concentration, use the formula:

• $M_1V_1 = M_2V_2$

• Example: To make 25.0 mL of 0.103 M solution from a stock solution, solve for $V_1$.

Stoichiometry in Solution Reactions

Neutralization Reactions

Neutralization involves an acid and a base reacting to form water and a salt. The stoichiometry of the reaction determines the volumes and concentrations needed.

• Example reaction: $H_2SO_4(aq) + 2NaOH(aq) \rightarrow Na_2SO_4(aq) + 2H_2O(l)$

• Calculate moles of acid and base, then use molarity and volume to determine required amounts.

Properties and Identification of Solutions

Identifying Solutions and Solubility

• Not all mixtures are solutions; suspensions and colloids are heterogeneous.

• Solubility depends on temperature, pressure, and nature of solute/solvent.

• Example: Gold dissolved in mercury forms an amalgam (solid solution).

Summary Table: Solution Types and Properties

Type of Solution	Solvent	Solute	Example	Electrolyte?
Solid Solution	Metal	Metal/Nonmetal	Steel (Fe + C)	No
Aqueous Solution	Water	Salt (NaCl)	Salt water	Yes (strong)
Aqueous Solution	Water	Sugar	Sugar water	No
Gas Solution	Air	Oxygen, Nitrogen	Atmosphere	No

Additional info: The above table summarizes common solution types encountered in introductory chemistry.