2. Properties of acids and bases Get 8 test tubes. Rinse all tubes well with water. Add acid to four tubes, base to the other four. Touch a drop of base to your finger. Record the feel in the chart (on the next slide). Wash your hands with water. Repeat for acid. Use a stirring rod, add base to the litmus and pH papers (for pH paper use a colour key to find a number). Record results. Repeat for acid. Into the four base tubes add: a) two drops of phenolphthalein, b) 2 drops of bromothymol, c) a piece of Mg, d) a small scoop of baking soda. Record results. Repeat for acid. Clean up (wash tubes, pH/litmus paper in trash).

3. Baking soda Magnesium Bromothymol Phenolphthalein Litmus (blue or red) pH (# from the key) Feel (choose slippery or not slippery) SourBitterTaste HCl(aq)NaOH(aq)Observations

4. BubblesNRBaking soda BubblesNRMagnesium *Yellow*BlueBromothymol *Cloudy/ white *PinkPhenolphthalein RedBlueLitmus (blue or red) 114pH (# from the key) Not slipperySlippery Feel (choose slippery or not slippery) SourBitterTaste HCl(aq)NaOH(aq)Observations *Usually, but not always

5. Historical views on acids The more recent Bronsted-Lowry concept is that acids are H + (proton) donors and bases are proton acceptors Ionization + ClH H H O + H H HO + O (e.g. H 2 SO 4 ) was originally thought to cause acidic properties. Later, H was implicated, but it was still not clear why CH 4 was neutral. Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H 3 O + (hydronium) ions in solution.

6. Bronsted-Lowry theory An acid is a substance from which a proton (H + ion) can be removed A base is a substance that can remove a proton (H + ion) from an acid An acid-base reaction involves the transfer of a proton

7. Types of Acids Acids may have more than one proton to donate. –Monoprotic acids contain 1 hydrogen ion i.e. HCl (aq) –Diprotic acids contain 2 hydrogen ions, i.e. H 2 SO 4 (aq) –Triprotic acids contain 3 hydrogen ions, i.e. H 3 PO 4(aq)

8. Conjugate acid-base pair Two molecules or ions that are related by the transfer of a proton (H+) are called a conjugate acid-base pair. (conjugate means “linked”)

9. The Bronsted-Lowry concept In this idea, the ionization of an acid by water is just one example of an acid-base reaction. Acids and bases are identified based on whether they donate or accept H +. “Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H +. + ClH H H O + H H HO + acidbase conjugate acidconjugate base conjugate acid-base pairs

10. Example: HBr(aq) + H 2 0(l) -> H 3 0 + (aq) + Br - (aq) Conjugate base of an acid is the particle that remains when a proton is removed from the acid (in this example: Br - (aq) Conjugate acid of a base is the particle that results when the base receives the proton from the acid (in this example: H 3 0 + (aq)

11. Practice problems Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: acidbase conjugate acidconjugate base HC 2 H 3 O 2 (aq) + H 2 O (l)  C 2 H 3 O 2 – (aq) + H 3 O + (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base OH – (aq) + HCO 3 – (aq)  CO 3 2– (aq) + H 2 O (l) conjugate acid-base pairs

12. Acids An acid is a substance that produces Hydrogen ions, H + (aq) in water (Arrhenius definition). The hydrogen ion (H + ) bonds with a water molecule to make a hydronium ion, H 3 0 + (aq) (H + -> H 2 0 = H 3 O + )

13. Strong acids A strong acid is an acid, which ionizes extremely well. Essentially all of the acid molecules are ionized. (lots of H 3 O + ) Example: HCl, HBr, HNO 3, H 2 SO 4, HClO 4 Example: HCl (aq) + H 2 O(l) -> H 3 0 + (aq) + Cl - (aq) H 2 SO 4 (aq) +2H 2 O(l) -> 2H 3 O + + SO 4 2- (aq) ( Ionization equations show how they react with water to make H 3 O + )

14. Weak acid A weak acid is an acid which ionizes poorly. Only a small percentage of the acid molecules actually ionize. (a few H 3 O + ) Example:HC 2 H 3 O 2 HC 2 H 3 O 2(aq) + H 2 O(l)  H 3 O+(aq) + C 2 H 3 0 2 -

15. Avoid confusing terms! Concentrated/Dilute vs Strong/Weak A strong acid such as HCl can be concentrated (12mol/L) or dilute (0.5mol/L) Concentrated or dilute refers to the amount of solute dissolved in the solvent Strong or weak- refers to the degree of dissociation of ions in solutions.

16. Bases A base is a substance that produces hydroxide ions, OH -, in water ( Arrhenius defintion ) A strong base is a base that dissociates 100% in aqueous solution. Example: NaOH(s)  Na + (aq) + OH - (aq) KOH(s) -> K + (aq) + OH - (aq) ( Ionization equations: show how they make ions)

17. Weak base A weak base is a base which ionizes poorly. Only a small percentage of the base molecules actually ionize.(a few OH - Example: NH 3 (aq) + H 2 O(l) -> NH 4 + (aq) + OH - (aq)