Solutions

Solutions

• Homogeneous mixtures of two or more substances.

• Form when attraction exists between solute and solvent molecules.

• Composed of a solvent (larger amount) and a solute (smaller amount).

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Homogeneous Mixtures

• Solvent: The major component that does the dissolving.

• Solute: The minority component that is being dissolved.

• Aqueous Solution: Water is the solvent.

Solutes

• Can be liquids, gases, or solids.

• Mix evenly throughout the solution.

• Have the same physical state as the solvent.

• Cannot be separated by filtration but can be by evaporation.

• Not visible, but can add color.

Solutions: Like Dissolves Like

• Solutions form when solute and solvent have similar polarities.

• Polar solutes dissolve in polar solvents.

• Nonpolar solutes dissolve in nonpolar solvents.

• In aqueous solutions, hydrogen bonding can override polarity.

Solutions with Ionic Solutes

• NaCl crystals undergo hydration as water molecules surround each ion.

• NaCl(s) \xrightarrow{H_2O(l)} Na^+(aq) + Cl^-(aq)

Strong Electrolytes

• Dissociate 100% in water, producing ions.

• Conduct an electric current strongly.

• NaCl(s) \xrightarrow{H_2O(l)} Na^+(aq) + Cl^-(aq)

Weak Electrolytes

• Dissociate slightly in water.

• Conduct electricity weakly.

• HF(aq) \leftrightarrow H^+(aq) + F^-(aq)

Nonelectrolytes

• Dissolve as molecules in water.

• Do not produce ions.

• Do not conduct electricity.

• CH3OH(l) \xrightarrow{H2O(l)} CH_3OH(aq)

Equivalents (Eq)

• Amount of an electrolyte or ion that provides 1 mole of electrical charge.

• Charge of positive ions balanced by negative ions.

• Concentrations in mEq/L.

• 1 Eq = 1000 mEq

Solubility

• Maximum amount of solute that dissolves in a specific amount of solvent.

• Temperature sensitive.

• Expressed as grams of solute per 100 grams of solvent.

Unsaturated Solutions

• Contain less than the maximum amount of solute.

• Can dissolve more solute.

Saturated Solutions

• Contain the maximum amount of solute that can dissolve.

• Have undissolved solute, with solute dissolving and recrystallizing at the same time.

• solute + solvent ⇌ saturated solution

Effect of Temperature on Solubility

• Solubility depends on temperature.

• Solubility of most solids increases with temperature.

• Solubility of gases decreases with temperature.

Solubility and Pressure

• Henry’s Law: The solubility of a gas in a liquid is directly related to the pressure of that gas above the liquid.

Solution Concentration

• Expressed as amount of solute/amount of solution.

• Units:

  • Mass percent (m/m)

  • Volume percent (v/v)

  • Mass/volume percent (m/v)

  • Molarity (moles solute/liters solution)

Mass Percent (m/m)

• Percent (m/m) = \frac{grams : of : solute}{grams : of : solute + grams : of : solvent} \times 100

Volume Percent (v/v)

• Percent (v/v) = \frac{mL : of : solute}{mL : of : solution} \times 100

Mass/Volume Percent (m/v)

• Percent (m/v) = \frac{grams : of : solute}{mL : of : solution} \times 100

Molarity (M)

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

Dilution of Solutions

• Solvent is added, increasing volume and decreasing concentration.

• C1V1 = C2V2

Colloids

• Transparent, do not separate, small inedible particles.

Suspensions

• Heterogeneous mixtures with large particles that settle.

Osmosis

• Water flows from lower to higher solute concentration until concentrations are equal.

Osmotic Pressure

• Pressure preventing additional water flow into the concentrated solution.

Reverse Osmosis

• Pressure greater than osmotic pressure forces solution through a membrane.

Isotonic Solutions

• Exert the same osmotic pressure as body fluids.

Hypotonic Solutions

• Lower solute concentration than RBCs; water flows into cells, causing them to burst (hemolysis).

Hypertonic Solutions

• Higher solute concentration than RBCs; water flows out of cells, causing them to shrink (crenation).

Dialysis

• Small solute particles pass through a membrane, while large particles are retained.