Solutions, Acids, and Bases

1. Solutions, Acids, and Bases Chapter 8

2. Solute The substance that is dissolved into the solution. examples: Sugar in kool-aid Salt in salt water CO2 in pop Solvent The substance that does the dissolving in a solution. examples: Most common is water. Parts of a solution

3. Dissolving • Three ways to dissolve a solute in a solvent: • Dissociation • Dispersion • Ionization

4. 1. Dissociation • The process in which an ionic compound separates into ions in a solution. (physical change) • Example: salt in water

5. 2. Dispersion • Breaking the solute into small pieces and spreading throughout the solvent. • Ex. Sugar in water • Physical change

6. 3. Ionization • The process in which neutral molecules lose or gain electrons. • Chemical change • Ex: HCl in water page 230

7. Conductivity • Many solutions can conduct an electric current if electrolytes are present. (ions) • Electrolytes = substances that will conduct an electric current when dissolved. Ex. NaCl, KCl, MgBr2

8. Freezing Point Depression • Lowering the freezing point of water by the addition of a solute • ex. salt. • Used on icy roads in winter • Ice-cream

9. Boiling point elevation • The addition of a solute to a liquid solvent will usually raise the boiling point of the solvent. • Adding salt to boil water when cooking

10. Heat of Solution • A measure of the amount of energy either absorbed or released when a solute dissolves in a solvent. • Can be endothermic or exothermic.

11. Rate of Solution • Speed at which solute dissolves in a solvent. • 1st Stirring the solution. Helps to move the solute particles away from the solid solute.

12. 2nd : Powdering the solute. Increases the surface area 3rd : Heating the solution. Speeds up the molecules Other factors:

13. Concentrated A large amount of solute dissolved in a solvent Dilute A little bit of solute dissolved in a solvent Concentration

14. Saturation • A solution that contains all the solute it can possibly hold at a given temperature is said to be saturated. • Unsaturated = contains less solute than it can possibly hold • Supersaturated = a solution that holds more solute than it should at a given temperature.

15. Supersaturation example: • Sodium acetate in water. • Used in commercial hand warmers.

17. Insoluble • A substance that will NOT dissolve in water.

18. “Like dissolves like” • Nonpolar solvents will dissolve nonpolar solutes. • examples: benzene & acetone • Polar solvents will dissolve polar solutes

19. 1.Temperature Increase in temp generally increases solubility of a solid in a liquid Increase in temp decreases solubility of a gas in a liquid. 2. Pressure Usually has little, if any, effect on solid and liquid solutes. Increase in pressure increases the solubility of a gas in a liquid. 2 factors that affect solubility:

20. Specific concentration • Can be defined as percent by volume or percent by mass • Example: 3% hydrogen peroxide or 25% fruit juice.

21. MOLARITY

22. Acids • Very important chemicals in everyday life processes.

23. Properties of acids: • Sour taste (never taste a chemical) • All contain hydrogen • Also called “proton donors” • React with active metals to produce hydrogen gas. (exp. 21) Zn + 2HCl ZnCl2 + H2

24. Indicators • Chemicals used to identify acids and bases by changing color. • ACIDS: • Litmus paper (blue to red) • Phenolphthalein (colorless) • Methyl Orange (orange to red) • Bromothymol Blue (changes to yellow)

25. Common acids • Sulfuric (H2SO4) used in car batteries • Nitric (HNO3) also fertilizers • Hydrochloric (HCl) stomach acid • Carbonic (H2CO3) carbonated drinks • Acetic (HC2H3O2) vinegar

26. Also very important in everyday processes. Bases

27. Properties of Bases: • Taste bitter; feel slippery • Contain hydroxide (OH) ions. • Known as “proton acceptors” • Phenolphthalein turns bright pink • Red litmus paper turns blue • Bromothymol blue turns blue • Methyl orange turns yellow

28. Common bases: • Sodium hydroxide NaOH making soap; drain cleaners • Potassium hydroxide KOH battery electrolyte • Calcium hydroxide Ca(OH)2 making plaster and drywall • Magnesium hydroxide Mg(OH)2antacids

29. Solutions of acids and bases • pH scale (page 247) • A numerical scale developed to measure the relative strengths of acids and bases • Ranges from 0 to 14 • 0 is the strongest acid • 14 is the strongest base.

30. Always forms water and a salt. Salt = ionic compound formed when a positive ion of a base combines with a negative ion of an acid. Neutralization. These are double replacement reactions. Examples: (on board) What happens when an acid and a base combine?

32. What determines if an acid is classified as “strong” or weak? • Which is stronger? 1 M acetic acid or 1M hydrochloric acid? • Strength is determined by how well the acid or base dissociates into solution. • Strong acids and strong bases are good electrolytes.

33. Buffers • A mixture of a weak acid or weak base with its salt. • Resists large changes in pH. • Examples: • Bicarbonate ions in your blood stream.

34. Assignment • Pages 257-258 • 1-10, 11, 13, 16, 20, 22, 23, 24, 27, 30, 31, 32