SolutionsChapter 6

Dr. Michael P. Gillespie

Properties of Solutions

• A solution is a homogenous (uniform) mixture of two or more substances.

• A solution is composed of one or more solutes, dissolved in a solvent.

• The solute is a compound of a solution that is present in lesser quantity than the solvent.

• The solvent is the solution component that is present in the largest quantity.

• An aqueous solution is one in which water is the solvent.

Solution

Example of a Solution

• When sugar (the solute) is added to water (the solvent), the sugar dissolves in the water to produce a solution.

• This mixture is an aqueous solution because water is the solvent.

Types of Solutions

• The dissolution of a solid into a liquid is the most common example of solution formation; however, it is possible to form solutions in gases and solids as well as liquids.

• Air is a gaseous mixture, but it is also a solution. Oxygen and some other trace gasses are dissolved in the gaseous solvent nitrogen.

• Many important biochemical reactions occur in liquid solutions, so our emphasis will be placed there.

Properties of Liquid Solutions

• Liquid solutions are clear and transparent with no visible particles of solute.

• They can be either colored or colorless.

Electrolyte and Nonelectrolyte

Solutions• An electrolyte is a material that dissolves in

water to produce a solution that conducts an electrical current.

• Solutions of electrolytes are formed from solutes that are soluble ionic compounds.• Good conductors of electricty• Sodium Chloride dissolving in water

• Solutions of nonelectrolytes are formed from nondissociating molecular solutes.• Nonconducting• Sugar dissolving in water

Electrolyte

True Solutions

• A true solution is a homogenous mixture with uniform properties throughout.

• The solute cannot be isolated from the solution by filtration.

• The particle size of the solute and solvent are about the same and both pass directly through the filter paper.

• Solute particles will not “settle out” over time.

True Solutions

• All of the molecules of solute and solvent are intimately mixed.

• The particles are in continuous motion and therefore maintain a homogenous, random distribution of solute and solvent particles.

• Volumes of solute and solvent are not additive.• 1 L of alcohol mixed with 1 L of water does not

result in exactly 2L of solution.• It depends upon how the molecules “fit

together”.

Solution, Pure Substance, or Colloidal

Suspension?• A beaker containing a clear liquid may

be a pure substance, a true solution, or a colloid.

Solution Vs. Pure Substance

• Only chemical analysis can distinguish between a pure substance and a true solution.

• A pure substance has only one component.

• A true solution has more than one substance, with the tiny particles homogenously intermingled.

Colloidal Suspension

• A colloidal suspension also consists of solute particles distributed throughout a solvent; however, the distribution is not completely homogenous, due to the size of the colloidal particles.

• Particles smaller than 1 nm are solution particles.

• Particles between 1 nm and 200 nm are colloids.

• Particles larger than 200 nm are precipitates (solid in contact with solvent).

Solution Vs. Colloidal Suspension

• To the naked eye, a colloidal suspension and a true solution appear identical. Neither the solute nor the colloid can be seen by the naked eye.

• Colloid particles are large enough to scatter light, whereas solute particles are not.

• When a beam of light passes through a colloidal solution, the large particles scatter light, and the liquid appears hazy. Similar to sunlight passing through fog.

• Tyndall effect – the light-scattering ability of solutions.

Suspension

• A suspension is a heterogeneous mixture that contains particles much larger than a colloidal suspension.

• These particles can settle out over time.

Colloidal Suspension

Polarity and Solubility

• “Like dissolves like”.

• Polar solutes are soluble in polar solvents.

• Nonpolar solutes are soluble in nonpolar solvents.

Degree of Solubility

• The degree of solubility is a measure of how much solute can dissolve in a given quantity of solvent.

• Factors influencing degree of solubility.• The magnitude of difference between

polarity of solute and solvent. (Inverse relationship)

• Temperature. (Usually increases solubility)• Pressure. (Greater influence on gases)

Saturation

• A saturated solution contains all of the solute that can be dissolved at a particular temperature.

• Decreasing the temperature typically decreases the amount of solute the solution can hold.

• The excess solute falls to the bottom of the container as precipitate (a solid in contact with a solution).

• Sometimes the excess solute stays in solution for a period of time. The solution is then said to be supersaturated (this is an unstable condition).

Precipitation

Solubility and Equilibrium

• When an excess of solute is added to a solvent, it begins to dissolve and continues to do so until it reaches a dynamic equilibrium between dissolved and undissolved solute.

• The rate of dissolution and precipitation eventually become equal.

• There is a continual exchange of particles between solid and liquid phases.

Henry’s Law

• Henry’s Law states that the number of moles of a gas dissolved in a liquid at a given temperature is directly proportional to the partial pressure of the gas.

• The gas solubility is directly proportional to the pressure of that gas in the atmosphere that is in contact with the liquid.

• Gases are most soluble at low temperatures.

• Henry’s law has a direct application to respiration in the lungs.

Henry’s Law

Henry’s Law

Concentration Based on Mass

• A solution concentration is the amount of solute dissolved in a given amount of solution.

• The concentration of a solution affects its physical properties such as melting and boiling points.

• The concentration also affects its chemical properties influencing its reactivity.

Weight / Volume Percent

• Concentration = amount of solute / amount of solution

• Concentration = grams of solute / milliliters of solution

• % concentration = grams of solute / milliliters of solution * 100%

Molarity

• Molarity (M) is the number of moles of solute per liter of solution.

• A Mole is a “collection” of atoms.

• 1 mol of atoms = 6.022 X 1023 atoms of an element. This number is Avogadro’s number.

• The mass of 1 mol of atoms is defined as the molar mass.

• One mole of atoms of any element contains the same number of atoms (6.022 X 1023 atoms).

Dilution

• Laboratory reagents are often purchased as concentrated solutions for safety, economic, and space limitation reasons.

• We often must dilute the solution to prepare a less concentrated form for our experiment.

Dilution

Colligative Properties

• Colligative properties are properties of solutions that depend on the concentration of the solute particles, rather than the identity of the solute.• 1. vapor pressure lowering• 2. freezing point depression• 3. boiling point elevation• 4. osmotic pressure

Vapor Pressure Lowering (Raoult’s

Law)• Raoult’s law states that, when a

nonvolatile solute is added to a solvent, the vapor pressure of the solvent decreases in proportion to the concentration of the solute.

• This has a direct effect on the freezing and boiling points of a solution.• The freezing point decreases.• The boiling point increases.

Freezing Point Depression

Boiling Point Elevation• The solute molecules interfere with the

rate at which liquid water molecules associate to form the solid state.• Salt is spread on ice in the winter

because it lowers the freezing point of water.

• 1 mol of glucose 1 mol of particles in solution

• 1 mol of sodium chloride 2 mol of particles in solution

Osmotic Pressure

• Some membranes are semipermeable. They all small solvent molecules such as water to cross; however, larger solute particles are too large to get through the small pores of the membrane.

• Osmosis is the diffusion of a solvent from a dilute solution to a more concentrated solution through a semipermeable membrane.

• Pressure must be applied to the more concentrated solution to stop the flow. Osmotic pressure is the amount of pressure required to stop the flow.

Osmosis

Hypertonic, Hypotonic, Isotonic

• Hypertonic – Water leaves a cell via osmosis. The cell undergoes crenation (shrinkage).

• Hypotonic – Water enters a cell via osmosis. The cell undergoes hemolysis (ruptures).

• Isotonic – Two solutions are isotonic if they have identical osmotic pressures.

Crenation & Hemolysis

Water as a Solvent

• Water is often referred to as the “universal solvent”.

• It is the principle biological solvent.

• Water is a polar molecule. Much of the matter on earth is polar. “Like dissolves like.”

Properties of Water

• Water is the only common molecule that exists in all three physical states of matter (solid, liquid, and gas) under natural conditions on earth.

• Water is essential for all life.

• Water is the most abundant molecule in living systems (70-95%).

• Water covers 70% of the earth’s surface.

Properties of Water

• Water has an unusually high specific heat and can therefore resist changes in temperature. It stabilizes temperatures on both earth and in the body.

• Water has a very high heat of vaporization.

• As water evaporates, the surface of the liquid cools. Perspiration helps to prevent overheating on a hot day or during strenuous exercise.

• The solid state of water is less dense than the liquid state (about 10% less dense).

Solutes in Blood• An electrolyte is a material that dissolves in water to

produce a solution that conducts an electrical current.

• The concentration of cations, anions, and other substances in body fluids is critical to health.

• The kidneys carefully regulate these levels.

• Na+ and K+ are the two most important cations in body fluids.

• Sodium is more abundant in intercellular fluids and potassium is more abundant in intracellular fluids. (Active transport)

• If potassium levels become too high from cell death (leakage) or too low from excessive sweating, heart failure can ensue.

Solutes in Blood

• The major anions in blood are Cl- and HCO3-.

• Chloride anion helps with acid-base balance, osmotic pressure, and oxygen transport by hemoglobin.

• Bicarbonate anion helps transport CO2 in the blood.

• Plasma proteins: blood clotting factors, immunoglobulins (antibodies), and albumins (carry non-polar substances).

• Nutrients and waste products.

Hemodialysis

• Dialysis – the kidneys remove waste products such as urea and uric acid as well as excess salts from the blood. This process is known as dialysis.

• Hemodialysis is the use of an artificial kidney to remove waste products from the blood.

Hemodialysis