Chapter 9: Solutions – GOB Chemistry Study Notes

Chapter 9: Solutions

9.1 Solutions

Solutions are homogeneous mixtures composed of two or more substances. The two main components are the solvent (the substance present in greater amount) and the solute (the substance present in lesser amount). Solutions can be found in various forms in nature and laboratory settings.

• Solvent: The medium in which the solute dissolves; usually present in larger quantity.

• Solute: The substance that is dissolved in the solvent; present in smaller quantity.

• Homogeneous mixture: Uniform composition throughout.

• Example: Salt water, where water is the solvent and salt is the solute.

Types of Solutes and Solvents

Solutes and solvents may be solids, liquids, or gases. The combination of these states leads to various types of solutions.

Type	Example	Primary Solute	Solvent
Gas in gas	Air	Oxygen (gas)	Nitrogen (gas)
Gas in liquid	Soda water	Carbon dioxide (gas)	Water (liquid)
Liquid in liquid	Vinegar	Acetic acid (liquid)	Water (liquid)
Solid in liquid	Seawater	Sodium chloride (solid)	Water (liquid)
Solid in solid	Brass	Zinc (solid)	Copper (solid)

Water as a Solvent

Water is one of the most common solvents in nature. It is a polar molecule and forms hydrogen bonds with other molecules, making it highly effective at dissolving ionic and polar substances.

• Polarity: Water molecules have a partial negative charge on oxygen and partial positive charges on hydrogen.

• Hydrogen bonding: Attraction between the hydrogen atom of one water molecule and the oxygen atom of another.

Formation of Solutions

Solutions form when the interactions between solute and solvent are strong enough to overcome the interactions within the solute and within the solvent. This process is governed by the principle "like dissolves like".

• Polar solvents dissolve polar solutes.

• Nonpolar solvents dissolve nonpolar solutes.

Solutions with Ionic and Polar Solutes

Ionic compounds such as NaCl dissolve in water through hydration, where water molecules surround each ion. Polar molecular compounds, like methanol, dissolve in water due to hydrogen bonding.

• Hydration: Water molecules surround and stabilize ions in solution.

• Polar solutes: Require polar solvents for dissolution.

9.2 Electrolytes and Nonelectrolytes

Electrolytes are substances that dissociate into ions when dissolved in water, allowing the solution to conduct electricity. They are essential for cellular and organ function in the body.

• Strong electrolytes: Dissociate completely in water, producing many ions.

• Weak electrolytes: Dissociate only partially, producing fewer ions.

• Nonelectrolytes: Dissolve as molecules, do not produce ions, and do not conduct electricity.

Equivalents

The equivalent (Eq) is a unit that expresses the amount of an ion that supplies one mole of charge. It is used in clinical chemistry to measure electrolyte concentrations.

Ion	Ionic Charge	Number of Equivalents in 1 Mole
Na+	1+	1 Eq
Ca2+	2+	2 Eq
Fe3+	3+	3 Eq
Cl-	1-	1 Eq
SO42-	2-	2 Eq

Calculating Equivalents

To convert between milliequivalents (mEq) and moles, use the following relationships:

• 1 Eq = 1 mole of charge

• 1 mEq = 0.001 Eq

Example calculation:

• Given 0.50 L of blood with 8.8 mEq/L Ca2+:

$0.50 \times \frac{8.8\,\text{mEq Ca}^{2+}}{1\,\text{L}} \times \frac{1\,\text{Eq Ca}^{2+}}{1000\,\text{mEq Ca}^{2+}} = 0.0044\,\text{Eq Ca}^{2+}$ $0.0044\,\text{Eq Ca}^{2+} \times \frac{1\,\text{mole Ca}^{2+}}{2\,\text{Eq Ca}^{2+}} = 0.0022\,\text{mole Ca}^{2+}$

Electrolytes in Body Fluids

Blood plasma maintains a charge balance, with the total number of positive charges equal to the total number of negative charges. Electrolyte concentrations are measured in mEq/L.

Electrolyte	Concentration (mEq/L)
Na+	138
K+	5
Mg2+	3
Ca2+	4
Cl-	110
HCO3-	30
HPO42-	4
Proteins	6

9.3 Solubility

Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature. Solutions can be classified as unsaturated, saturated, or supersaturated.

• Unsaturated solution: Contains less solute than the maximum possible.

• Saturated solution: Contains the maximum amount of solute; excess solute remains undissolved.

• Supersaturated solution: Contains more solute than normally possible; unstable.

Effect of Temperature and Pressure on Solubility

Solubility of solids generally increases with temperature, while solubility of gases decreases as temperature increases. The solubility of gases is also directly related to the pressure above the liquid (Henry's Law).

• Henry's Law: At higher pressures, more gas molecules dissolve in the liquid.

Solubility Rules for Ionic Compounds

Not all ionic compounds are soluble in water. Solubility rules help predict whether a compound will dissolve.

Soluble If It Contains	Insoluble If It Contains
Li+, Na+, K+	None
NO3-, C2H3O2-	None
Cl-, Br-, I-	Ag+, Pb2+, Hg22+
SO42-	Ba2+, Pb2+, Ca2+, Sr2+, CO32-, PO43-, S2-, OH-

9.4 Concentration of a Solution

Concentration expresses the amount of solute in a given amount of solution. Common units include mass percent, volume percent, mass/volume percent, and molarity.

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

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

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

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

9.6 Properties of Solutions

Solutions, colloids, and suspensions are different types of mixtures. Their properties depend on particle size and behavior in the mixture.

• Solution: Homogeneous, particles do not settle out.

• Colloid: Heterogeneous, particles are dispersed but do not settle.

• Suspension: Heterogeneous, particles settle out over time.

Osmosis and Osmotic Pressure

Osmosis is the movement of water across a semipermeable membrane from a region of lower solute concentration to higher solute concentration. Osmotic pressure is the pressure required to stop this flow.

Isotonic, Hypotonic, and Hypertonic Solutions

• Isotonic: Same osmotic pressure as body fluids; cells retain their normal shape.

• Hypotonic: Lower solute concentration than cells; water enters cells, causing hemolysis.

• Hypertonic: Higher solute concentration than cells; water leaves cells, causing crenation.

Dialysis

Dialysis is a process where solvent and small solute particles pass through an artificial membrane, while larger particles are retained. It is used in medical treatments such as hemodialysis to remove waste from blood.

Additional info: All explanations have been expanded for academic clarity and completeness. Tables and formulas have been recreated and formatted for study purposes.