Chapter 12 Solutions Types of Mixtures

Classification Scheme

Classifying Matter

Colloids Many colloids look similar to solutions because their particles cannot be seen. Look homogeneous to the naked eye. Tyndall effect Occurs when light is scattered by colloidal particles dispersed in a transparent medium. Colloids frequently appear "murky" or "opaque". Example: Milk

Colloids The Tyndall effect can be used to distinguish between a solution and a colloid. Mixture of water And NaCl Mixture of water and gelatin <--Beam of Light

Table 3 – Page 404 Properties of Solutions, Colloids and Suspensions

Solutions Sugar and water Soluble Sugar is described as “soluble in water.” Soluble Capable of being dissolved. When sugar dissolves, all its molecules become uniformly distributed among the water molecules. The solid sugar is no longer visible.

Solution Homogeneous mixture of two or more substances in a single phase. “Particle-by-particle mixture”

Components of Solutions Solute Substance dissolved in a solution Solvent Substance in which a solute dissolves

Saltwater solute + solvent = solution What is the solvent? What is the solute? What is the solvent? solute + solvent = solution

Review What type of mixture is a: Solution Suspension Colloid Homogeneous or Heterogeneous

Review What is an example of a solution, colloid and suspension? How can one distinguish a solution from a colloid if both appear homogeneous?

Electrolytes vs. Nonelectrolytes A substance that dissolves in water to give a solution that conducts electric current Examples: NaCl (any soluble ionic compound) Dissociation NaCl(s)  Na+(aq) + Cl-(aq) HCl (polar molecular compounds) Ionization HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq)

Electrolytes vs. Nonelectrolytes A substance (solute) that dissolves in water (solvent) to give a solution that does NOT conduct electric current. Compounds that do NOT ionize in water Limited to covalent bonds Examples: Sugar (C6H12O6) Methane (CH4) Benzene (C6H6) Ethanol (C2H5OH)

Electrical Conductivity of Solutions

Dissociation vs. Ionization Ions of the ionic compound split apart but do not react with the water. Ex: NaCl(s)  Na+(aq) + Cl-(aq) Ionization The ionic compound reacts with the water to form ions. Ex: HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq)

Strong and Weak Electrolytes Substances that yield ions Conduct an electric current in solution. The strength with which substances conduct an electric current is related to their ability to form ions in solution. Strong and weak electrolytes differ in the degree of ionization or dissociation.

Strong Electrolytes Any compound whose dilute aqueous solutions conduct electricity well. Due to the presence of all or almost all of the dissolved compound in the form of ions. To whatever extent they dissolve in water, they yield only ions. Examples: HCl, HBr, HI, NaOH All soluble ionic compounds

Weak Electrolytes Any compound whose dilute aqueous solutions conduct electricity poorly. Due to the presence of a small amount of the dissolved compound in the form of ions. Some molecular compounds form aqueous solutions that contain not only dissolved ions but also some dissolved molecules that are not ionized. Examples: CH3COOH             CH3COOH  --------->  CH3COO-  +    H+ before             100%                            0                 0 after                98.2%                         1.8%           1.8%

What are the electrolytes in Gatorade? Key electrolytes Sodium Potassium Chloride Gatorade Website: http://www.gatorade.com/hydration/replenish/ Body Tour: http://www.gssiweb.com/interactive_tools.aspx Drink Label: http://www.gssiweb.com/Article_Detail.aspx?articleid=572&level=2&topic=1

Why should people drink sports drinks? “To rapidly replace the fluids and electrolytes lost through sweat, and provide energy for active muscles." Sweating is your body’s way of cooling down. Dehydration is the penalty we pay. Drinking sports drinks during physical activity can reduce dehydration to zero. Physical activity also increases our need for the carbohydrate energy that some sports drinks provide. Able to exercise longer and harder. Reference -- Bob Murray, Ph.D., FACSM, Director, Gatorade Sports Science Institute

Factors affecting the rate of dissolution Surface Area Agitating Temperature

Solubility For every combination of solvent with a solid solute at a given temperature: Limit to the amount of solid that can be dissolved. The point at which this limit is reached for any solute-solvent combination depends on the nature of the: Solute Solvent Temperature

Solubility Amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature. Example: The solubility of sugar is 204 g per 100 g of water at 20°C. Solubility's vary widely, and must be determined experimentally. Usually given as grams of solute per 100 g of solvent at a given temperature.

Particle Model for Soluble Particles

Solution Equilibrium When maximum solubility is reached: Molecules are returning to the solid form at the same rate at which they are going into solution. Physical state in which the opposing processes of dissolution and crystallization of a solute occur at the same rates.

Example of Solution Equilibrium Saturated solution in a closed system Solute is recrystallizing at the same rate that it is dissolving. Appears that there is no activity in system but the opposing processes are occurring at the same rate.

Saturated vs. Unsaturated Saturated Solution Contains the maximum amount of dissolved solute. If more solute is added to a saturated solution, it falls to the bottom of the container and does not dissolve. Result of equilibrium being established between ions leaving and entering the solid phase.

Solubility Curves

Soluble Substances in Water Any polar molecule C12H22O11 Molecular compound with weak intermolecular forces Bonds broken and molecules released in solution

Soluble Substances in Water NaCl Ionic solid salts Ions released into solution Dissociation HCl Reacts with water to form ions Ionization

Dissolving Ionic Compounds in Aqueous Solutions Polarity of water molecules Important role in the formation of solutions of ionic compounds in water. Slightly charged parts of water molecules attract the ions in the ionic compounds and surround them. Separating them from the crystal surface and drawing them into the solution. Hydration Solution process with water as the solvent. The ions are said to be hydrated.

Liquid solutes and solvents Oil and water do not mix because oil is nonpolar whereas water is polar. Two polar substances, or two nonpolar substances, on the other hand, form solutions together easily because their intermolecular forces match. Immiscible Liquids that are not soluble in each other Miscible Liquids that dissolve freely in one another in any proportion

Effect of pressure on solubility Changes in pressure have very little effect on the solubilities of liquids or solids in liquid solvents. Increases in pressure  increase gas solubilities in liquids. Equilibrium is established between a gas above a liquid solvent and the gas dissolved in a liquid. As long as this equilibrium is undisturbed, the solubility of the gas in the liquid is unchanged at a given pressure:

Effects of Temperature on Solubility of Gases Increasing the temperature usually decreases gas solubility. As temperature increases, the average kinetic energy of molecules increases. A greater number of solute molecules are therefore able to escape from the attraction of solvent molecules and return to the gas phase. At higher temperatures, therefore, equilibrium is reached with fewer gas molecules in solution, and gases are generally less soluble.

Solubility vs. Temperature

Solubility Curve