Solutions and Concentration in GOB Chemistry: Study Notes Areeg

Solutions in Chemistry

Definition and Components of Solutions

A solution is a homogeneous mixture in which one substance (the solute) is uniformly dispersed in another substance (the solvent).

• Solute: The substance present in the smaller amount; it is dissolved in the solvent.

• Solvent: The substance present in the larger amount; it dissolves the solute.

• Example: In a saltwater solution, NaCl is the solute and water is the solvent.

Water as a Solvent

Water is the most common solvent in chemistry due to its polarity and ability to form hydrogen bonds.

• The O-H bond in water is polar, and the overall H2O molecule is polar due to its bent shape.

• Hydrogen bonds form between the hydrogen atom in one water molecule and the oxygen atom in another.

• Example: Water dissolves ionic compounds like NaCl by surrounding ions with water molecules.

Formation of Solutions: "Like Dissolves Like"

The solubility of substances depends on the polarity of both solute and solvent.

• Polar substances dissolve in polar solvents.

• Nonpolar substances dissolve in nonpolar solvents.

• Example: Sugar (polar) dissolves in water (polar); oil (nonpolar) dissolves in hexane (nonpolar).

Solute	Solvent	Will Form Solution?
Polar	Polar	Yes
Nonpolar	Nonpolar	Yes
Polar	Nonpolar	No
Nonpolar	Polar	No

Electrolytes and Nonelectrolytes

Definitions

• Electrolytes: Substances that produce ions in solution and conduct electricity.

• Nonelectrolytes: Substances that do not produce ions in solution and do not conduct electricity.

Types of Electrolytes

• Strong electrolytes: Completely dissociate into ions in water (e.g., NaCl, KBr).

• Weak electrolytes: Partially dissociate into ions (e.g., HF, CH3COOH).

• Nonelectrolytes: Do not dissociate into ions (e.g., sugar, ethanol).

Type of Solute	In Solution	Species of Particles	Conducts Electricity?	Examples
Strong Electrolyte	Dissociates completely	Ions only	Yes	NaCl, KBr, Mg(NO3)2
Weak Electrolyte	Dissociates partially	Mostly molecules, some ions	Weakly	HF, H2CO3
Nonelectrolyte	No ionization	Molecules only	No	CH3OH, C6H12O6

Solubility and Types of Solutions

Solubility

Solubility is the amount of solute that can dissolve in a given amount of solvent at a specific temperature.

• Saturated solution: Contains the maximum amount of solute that can dissolve at a given temperature.

• Unsaturated solution: Contains less than the maximum amount of solute.

• Supersaturated solution: Contains more than the maximum amount of solute; usually unstable.

Effect of Temperature on Solubility

• Solubility of most solids increases as temperature increases.

• Solubility of gases decreases as temperature increases.

• Example: More sugar dissolves in hot tea than in cold tea.

Henry's Law

The solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid.

• Example: CO2 in carbonated beverages is kept dissolved under pressure.

Concentration of Solutions

Types of Concentration Expressions

• Percent concentration: Expressed as mass/mass (m/m), volume/volume (v/v), or mass/volume (m/v).

• Molarity (M): Moles of solute per liter of solution.

Concentration Units	Mass Percent (m/m)	Volume Percent (v/v)	Mass/Volume Percent (m/v)	Molarity (M)
Solute	g	mL	g	mol
Solution	g	mL	mL	L

Calculating Mass Percent (m/m)

• Formula: $\text{Mass percent (m/m)} = \frac{\text{mass of solute (g)}}{\text{mass of solution (g)}} \times 100$

• Example: If 25 g of KCl is added to 125 g of H2O, mass percent = $\frac{25}{150} \times 100 = 16.7\%$

Calculating Volume Percent (v/v)

• Formula: $\text{Volume percent (v/v)} = \frac{\text{volume of solute (mL)}}{\text{volume of solution (mL)}} \times 100$

• Example: 12 mL Br2 in 250 mL solution: $\frac{12}{250} \times 100 = 4.8\%$

Calculating Mass/Volume Percent (m/v)

• Formula: $\text{Mass/volume percent (m/v)} = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} \times 100$

• Example: 75 g Na2SO4 in 250 mL solution: $\frac{75}{250} \times 100 = 30\%$

Calculating Molarity (M)

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

• Example: 5.0 g KI in 250 mL solution: First, calculate moles of KI, then divide by 0.250 L.

Dilution of Solutions

Process and Formula

In dilution, a solvent (usually water) is added to a solution, increasing the volume but keeping the number of moles of solute constant.

• Formula: $M_1V_1 = M_2V_2$

• Example: To prepare 200 mL of 0.250 M KNO3 from a 6.00 M KNO3 solution, use the formula to solve for the required volume.

Application Problems and Conversions

Using Molarity and Percent Concentration as Conversion Factors

• Use molarity to convert between grams, moles, and volume of solution.

• Use percent concentration to find the mass or volume of solute in a given amount of solution.

• Example: How many liters of 1.00 M NaCl are needed to provide 5.00 g of NaCl?

Percent Concentration	Meaning	Conversion Factors
10% (m/m) NaCl solution	10 g NaCl in 100 g solution	10 g NaCl/100 g solution
12% (v/v) ethanol solution	12 mL ethanol in 100 mL solution	12 mL ethanol/100 mL solution
5% (m/v) glucose solution	5 g glucose in 100 mL solution	5 g glucose/100 mL solution
6.0 M HCl solution	6.0 moles HCl in 1 L solution	6.0 mol HCl/1 L solution

Summary Table: Classification of Solutes in Aqueous Solutions

Type of Solute	In Solution	Species of Particles	Conducts Electricity?	Examples
Strong Electrolyte	Dissociates completely	Ions only	Yes	NaCl, KBr, Mg(NO3)2
Weak Electrolyte	Dissociates partially	Mostly molecules, some ions	Weakly	HF, H2CO3
Nonelectrolyte	No ionization	Molecules only	No	CH3OH, C6H12O6

Key Equations

• $\text{Mass percent (m/m)} = \frac{\text{mass of solute (g)}}{\text{mass of solution (g)}} \times 100$

• $\text{Volume percent (v/v)} = \frac{\text{volume of solute (mL)}}{\text{volume of solution (mL)}} \times 100$

• $\text{Mass/volume percent (m/v)} = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} \times 100$

• $\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}$

• $M_1V_1 = M_2V_2$ (Dilution equation)

Additional info:

• Practice problems and objectives are included to reinforce understanding of solution formation, solubility, electrolytes, and concentration calculations.

• Tables and diagrams referenced in the notes are described in text and formatted in HTML for clarity.