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Tuesday, March 15 th : “A” Day Agenda  Homework questions/problems/collect  Quiz over section 13.3: “Solubility/Dissolving Process”  Section 13.4:

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Presentation on theme: "Tuesday, March 15 th : “A” Day Agenda  Homework questions/problems/collect  Quiz over section 13.3: “Solubility/Dissolving Process”  Section 13.4:"— Presentation transcript:


2 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

3 Homework  Pg. 477: #1-8  Questions/Problems?  Hand in

4 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…

5 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?

6 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.

7 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.

8 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.

9 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)

10 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)

11 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.

12 Electrical Conductivity of Solutions

13 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.

14 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

15 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.

16 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.

17 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.

18 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)

19 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.

20 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.

21 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.

22 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.

23 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.

24 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.

25 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.

26 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

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