Tuesday, March 15 th : “A” Day Agenda Homework questions/problems/collect Quiz over section 13.3: “Solubility/Dissolving Process” Section 13.4: “Physical Properties of Solutions” Homework: Section review, pg. 486: #1-10 Concept review: “Physical Properties of Solutions” *Quiz over this section next time* Looking Ahead: Chapter 13 Test/Concept Review Due Wednesday, March 23 rd
Homework Pg. 477: #1-8 Questions/Problems? Hand in
Quiz Section 13.3: “Solubility and the Dissolving Process” You may use your guided notes, your book, and a partner of your choice to complete this review/quiz…
Electrical Conductivity in Solutions Some substances conduct electricity and some cannot. Conductivity: the ability to conduct an electric current. The conductivity of a substance depends on: 1. whether it contains charged particles 2.are the particles able to move?
Electrical Conductivity in Solution Electrons move freely within a metal, thus allowing it to conduct electricity. Solid NaCl contains ions, but they cannot move, so solid NaCl is not a conductor. An aqueous solution of ionic compounds, such as NaCl, contains charged ions, which can move about. Solutions of ionic compounds conduct electricity. Pure water does not conduct electricity.
Electrolytes Provide Ions in Solution Electrolyte: a substance that dissolves in water to give a solution that conducts an electric current. Strong electrolytes completely dissociate into ions and conduct electricity well. Ionic compounds are usually strong electrolytes. Weak electrolytes provide few ions in solution. Even in high concentrations, solutions of weak electrolytes conduct electricity weakly. Covalent compounds may be strong electrolytes, weak electrolytes, or nonconductors.
Electrical Conductivities Span a Wide Range The extent to which electrolytes dissociate into ions is indicated by the conductivity of their solutions. The sugar sucrose does not ionize at all in solution. It is a non-electrolyte and does not conduct electricity. Non-electrolyte: a liquid or solid substance that does not allow the flow of an electric current, either in solution or in its pure state, such as water or sucrose.
Acids react with water to form the hydronium ion, H 3 O +. Hydronium ion: an ion consisting of a proton combined with a molecule of water; H 3 O +. Acetic acid is a weak electrolyte. When added to water, only about 1% of acetic acid molecules ionize into hydronium ions and acetate ions. Water + Acetic Acid Hydronium Ion + Acetate Ion H 2 O (l) CH 3 COOH (aq) H 3 O + (aq) CH 3 COO - (aq)
Acids react with water to form the hydronium ion, H 3 O +. Hydrogen chloride dissolves in water to form a strongly conducting solution called hydrochloric acid. Hydrogen chloride is a strong electrolyte because it ionizes completely, as shown by the following equation: HCl(g) + H 2 O(l) → H 3 O + (aq) + Cl − (aq)
Conductivities Span a Wide Range Keep in mind that the use of the terms strong and weak have nothing to do with concentration. The term strong means that the substance provides a high proportion of ions in solution.
Tap Water Conducts Electricity Rainwater in a relatively unpolluted area, is essentially a non-conductor of electricity. Water from wells, lakes, or rivers has been in contact with soil and rocks, which contain ionic compounds that dissolve in the water. The more ions dissolved in water, the more it conducts electricity.
Freezing-Point Depression The physical properties of water are changed when substances dissolve in it. Salt can be added to icy sidewalks to melt the ice. The salt actually lowers the freezing point of water. Ice is able to melt at a lower temperature than it normally would. This change is called freezing-point depression
Boiling-Point Elevation Non-volatile solutes such as salt also increase the boiling point of a solvent. This change is called boiling-point elevation. For example, glycol in a car’s radiator increases the boiling point of water in the radiator, which prevents overheating. It also lowers the freezing point, preventing freezing in cold weather.
Colligative Properties Any physical effect of the solute on the solvent is a colligative property. Colligative property: a property of a substance or system that is determined by the number of particles present in the system but independent of the properties of the particles themselves. What? It doesn’t matter what the particles are, just how many there are there.
Only the Concentration of Dissolved Particles Is Important Any solute, whether an electrolyte or a non- electrolyte, contributes to the colligative properties of the solvent. The greater the particle concentration is, the greater the boiling-point elevation or the freezing-point depression is.
The greater the particle concentration is, the greater the boiling point elevation or the freezing point depression is. 1 mole of NaCl is expected go give twice the amount of change as 1 mole of sucrose, C 12 H 22 O 11 : NaCl (s) Na + (aq) + Cl - (aq) (2 dissolved particles) C 12 H 22 O 11 (s) C 12 H 22 O 11 (aq) (1 dissolved particle) CaCl 2 has about 3X the effect as 1 mol of sucrose: CaCl 2 (s) Ca 2+ (aq) + 2 Cl - (aq) (3 dissolved particles)
Dissolved Solutes Lower the Vapor Pressure of the Solvent Colligative properties are all caused by a decrease in the vapor pressure of the solvent. A solution has fewer solvent particles per volume than the pure solvent has, so fewer solvent particles are available to vaporize. Vapor pressure will therefore be decreased in proportion to the number of solute particles.
How Soap Works Soap molecules contain long non-polar hydrocarbon chains, which are soluble in the non-polar dirt and oils on your skin. Soap molecules also have negatively charged ends, which are soluble in the water you use to wash your hands. Soap: a substance that is used as a cleaner and dissolves in water.
Surfactants Soap is a surfactant. Surfactant: a compound that concentrates at the boundary surface between two immiscible phases, solid-liquid, liquid-liquid, or liquid-gas. A detergent is a surfactant that is used for cleaning purposes. Detergent: a water-soluble cleaner that can emulsify dirt and oil. Usually these are synthetic and not natural products. A soap is a particular type of detergent and a natural product.
Surfactants Soap is an emulsifying agent. Emulsion: any mixture of two or more immiscible liquids in which one liquid is dispersed in the other. An emulsifying agent links the polar and non- polar phases. Without an emulsifying agent, polar and non- polar molecules remain separate. Lecithin is an emulsifying agent that is used in salad dressing to keep the oil and vinegar mixed.
Soaps are Actually Salts Like other salts, when dissolved, soaps form ions. Unlike other salts, the polyatomic anion of soap contains a long non-polar part. It is this non-polar hydrocarbon chain that is soluble with oils and dirt.
Hard Water Limits Soap’s Detergent Ability Soaps are not ideal cleansing agents because the salts of some of their anions are insoluble in water, especially salts of calcium, magnesium, and iron(II). Hard water has high concentrations of these cations, which react with anions such as the palmitate anion to form insoluble salts. This is where bathtub scum comes from.
Synthetic Detergents Outperform Soaps in Hard Water Synthetic detergents can be used in hard water without forming precipitates and scum. Today, almost all laundry products and shampoos contain synthetic detergents. The basic structure of a synthetic detergent is the same as the structure of a soap. The long non-polar tail of the detergent is connected to the salt of a sulfonic acid which does not form insoluble precipitates with magnesium or calcium, which are found in hard water.
Homework Section review, pg. 486: #1-10 Concept review: “Physical Properties of Solutions” *Quiz next time over this section* Next Time: Mrs. Klima/Work Day Quiz/Chapter Review/Concept Review/3Q Assessment