Chapter 12Solutions

• 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 waterand gelatin

Mixture of waterAnd NaCl

<--Beam of Light

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

Solutions

• Sugar and water – 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

• 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

• Electrolyte• 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

• Nonelectrolyte• 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

• Dissociation– 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

• 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:

gas + solvent solution

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