2. What Are Solutions?

3. Solution: homogeneous mixture of 2 or more substances Solution: homogeneous mixture of 2 or more substances –Solid, liquid, or gas –Solvent: dissolving medium –Solute: substance that dissolves –When in solution, you cannot distinguish solvent and solute

4. What is a Solution? Soluble – a substance that can dissolve in a given solvent Soluble – a substance that can dissolve in a given solvent –Miscible: two liquids that can dissolve in each other Example: water and antifreeze Example: water and antifreeze Insoluble – substance cannot dissolve Insoluble – substance cannot dissolve –Immiscible: two liquids that cannot dissolve in each other Example: oil & water Example: oil & water

5. Why Do Some Substances Dissolve and not Others? To dissolve, solute particles must dissociate from each other and mix with solvent particles To dissolve, solute particles must dissociate from each other and mix with solvent particles –Attractive forces between solute and solvent must be greater than attractive forces within the solute Process of surrounding solute particles with solvent particles is called SOLVATION Process of surrounding solute particles with solvent particles is called SOLVATION –In water, it is also called HYDRATION

6. Aqueous Solutions of Ionic Compounds Remember: Remember: –Water molecules are polar (+ and – ends) –Water molecules are in constant motion When you put salt in water, water molecules collide with surface of crystal When you put salt in water, water molecules collide with surface of crystal –Charged ends of water attract ions of salt –Dipole interaction (water/salt) is stronger than ions in crystal, so it pulls them away

7. Solvation

8. Aqueous Solutions of Molecular Compounds Water is also a good solvent for many molecular compounds (Example: sugar) Water is also a good solvent for many molecular compounds (Example: sugar) –Sugar has many O-H bonds (polar) –When water is added, the O-H bond becomes a site for hydrogen bonding with water –Water’s hydrogen bonds pulls the sugar molecules apart –Oil is not a good solute because it has many C-H bonds (not polar) and few or no O-H (polar) bonds

9. Factors that Affect Solvation Rate Increase Solvation Rate (Dissolve Faster) by: Increase Solvation Rate (Dissolve Faster) by: –Agitation (stirring) –Increase surface area (make particles smaller) –Temperature (make it hotter) All these increase the number of collision between water and the solute All these increase the number of collision between water and the solute

10. Heat of Solution During Solvation it takes energy to make the solute particles come apart. During Solvation it takes energy to make the solute particles come apart. Solvent particles must also move apart Solvent particles must also move apart This energy requirements is called “Heat of Solution” This energy requirements is called “Heat of Solution”

11. Solubility Has Anyone ever made rock candy? Has Anyone ever made rock candy? –How much water does it take to dissolve the sugar at room temperature? –What happens when we raised the temperature? Only a limited amount of solute can dissolve in a given amount of solvent Only a limited amount of solute can dissolve in a given amount of solvent Every solute is unique for the solvent Every solute is unique for the solvent This is ‘Solubility’ – the amount of solute that can dissolve in a given amount of solvent at a specified temperature and pressure This is ‘Solubility’ – the amount of solute that can dissolve in a given amount of solvent at a specified temperature and pressure

12. Solubility Continued Solubility can also be understood at the particle level: Solubility can also be understood at the particle level: –As particles collide, some particles are deposited back to the solute –Some particles are removed from the solute. –When the rate of deposit equals the rate of solvation, then the solution is SATURATED Saturated Solution – no more solute can be dissolved in the solvent at this temperature and pressure Saturated Solution – no more solute can be dissolved in the solvent at this temperature and pressure Unsaturated Solution – there is still room for more solute to be dissoved Unsaturated Solution – there is still room for more solute to be dissoved

13. Factors that Affect Solubility Most substances are MORE soluble at high temperature than at low Most substances are MORE soluble at high temperature than at low –If you dissolve a substance until saturated at high temperature and then reduce the temperature, the solution becomes “supersaturated” –Supersaturated solutions are unstable A small change makes the solute reappear A small change makes the solute reappear Rock candy worked that way. How? Rock candy worked that way. How?

14. Solubility SATURATED SOLUTION no more solute dissolves UNSATURATED SOLUTION more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form concentration

15. Solubility Solubility Solubility Curve Solubility Curve –shows the dependence of solubility on temperature

16. Solubility Chart

17. Solution Concentration Section 15.2

18. Expressing Concentration Concentration is a measure of how much solute is dissolved in a specific amount of solvent. Concentration is a measure of how much solute is dissolved in a specific amount of solvent. Concentration can be qualitative or quantitative Concentration can be qualitative or quantitative –Qualitative: strong, weak, etc. –Quantitative: percent by mass, percent by volume, molarity, molality

19. Molarity Molarity is the most common method of expressing concentration in Chemistry Molarity is the most common method of expressing concentration in Chemistry Molarity is moles of solute in 1 liter of solution. Molarity is moles of solute in 1 liter of solution. –You make it by taking 1 mole of a solute and filling up with solvent to the 1 liter level. Molarity (M) = Moles of solute Liters of solution

20. Heterogeneous Mixtures Chapter 15.4

21. Types of Heterogeneous Mixtures Heterogeneous Mixtures Heterogeneous Mixtures –Look like a solution, but are really mixtures –Mixtures of substances that exist in 2 different phases 2 Types: 2 Types: –Suspensions –Colloids Solutions: Solutions: –Particles of solute are atomic sized compared to solvent

22. Suspensions Particle Size Particle Size –Suspended particles are large compared to solvent Larger than 1000 nm for solvated particles Larger than 1000 nm for solvated particles –CAN be filtered When stirred, solid-like state begins to flow like a liquid When stirred, solid-like state begins to flow like a liquid –Called Thixotropic Examples Examples –housepaint

23. Colloids Particle Size Particle Size –Particles of solute are intermediate sized (between atomic and large suspension sized) compared to solvent –Between 1 nm and 1000 nm diameter Cannot be Separated by filtration or settling Cannot be Separated by filtration or settling –Example: milk, butter, cheese,

24. Colloids Types of Colloids Types of Colloids –Solid Sol: Solid in solid (gemstones) –Sol: Solid in Liquid (Blood, gelatin) –Solid emulsion: Liquid in solid (butter, cheese) –Emulsion: liquid/liquid (milk, mayonaise) –Solid foam: gas/solid (marshmallows, soap that floats) –Foam: gas/liquid (whipped cream, beaten egg whites) –Aerosol: solid/gas (smoke, dust in air) –Aerosol: liquid/gas (clouds, spray deodorant

25. Tyndall Effect Dilute Colloids sometimes appear as clear solutions (concentrated colloids do not) Dilute Colloids sometimes appear as clear solutions (concentrated colloids do not) –Because particles are too small to be seen with naked eye –But: dispersed colloid particles are large enough to scatter light Tyndall effect Tyndall effect –Solutions do not scatter light (particles are too small)

26. Tyndall Effect SolutionColloid

27. The ammeter measures the flow of electrons (current) through the circuit.  If the ammeter measures a current, and the bulb glows, then the solution conducts.  If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting. Electrolytes vs. Nonelectrolytes

28. An electrolyte is: A substance whose aqueous solution conducts an electric current. A nonelectrolyte is: A substance whose aqueous solution does not conduct an electric current. Try to classify the following substances as electrolytes or nonelectrolytes… Definition of Electrolytes and Nonelectrolytes

29. 1.Pure water 2.Tap water 3.Sugar solution 4.Sodium chloride solution 5.Hydrochloric acid solution 6.Lactic acid solution 7.Ethyl alcohol solution 8.Pure sodium chloride Electrolytes?

30. ELECTROLYTES:NONELECTROLYTES: Tap water (weak) NaCl solution HCl solution Lactate solution (weak) Pure water Sugar solution Ethanol solution Pure NaCl But why do some compounds conduct electricity in solution while others do not…? Answers to Electrolytes