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).

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

pH There are many ways to consider acids and bases. One of these is pH. Read pg [H + ] is critical in many chemical reactions. A quick method of denoting [H + ] is via pH. By definition pH = – log [H + ], [H + ] = 10 -pH The pH scale, similar to the Richter scale, describes a wide range of values An earthquake of 6 is 10 as violent as a 5 Thus, the pH scale condenses possible values of [H + ] to a 14 point scale (fig. 2, p370) Also, it is easier to say pH = 7 vs. [H + ] = 1 x 10 –7

Calculations with pH Ans: x 10 –8 M Try questions 2 and 6 (a-b) on page 375 Q: What is the pH if [H + ]= 6.3 x 10 –5 ? pH = – log [H + ] (6.3, exp or EE, 5, +/-, log, +/-) (-, log, 6.3, exp or EE, -, 5) Q: What is the [H + ] if pH = 7.4? [H + ] = 10 –pH mol/L (10, x y, 7.4, +/-, =) (10, ^, -, 7.4, =)

Pg a)pH = – log [H + ] = – log [1x10 –8 ] = 8.0 b)pH = – log [H + ] = – log [1x10 –7 ] = 7.0 c)pH = – log [H + ] = – log [2.5x10 –6 ] = 5.60 d)pH = – log [H + ] = – log [1.3x10 –4 ] = a)[H + ] = 10 –pH = 10 –5.4 = 4 x 10 –6 mol/L b)[H + ] = 10 –pH = 10 –5.72 = 1.9 x 10 –6 mol/L

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.

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

Practice problems Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: Reference: pg. 386 – 387 Try Q18 (p389), Q 8 & 11 (p392): do as above 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

acidbase conjugate acidconjugate base HF (aq) + SO 3 2– (aq) F – (aq) + HSO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base CO 3 2– (aq) + HC 2 H 3 O 2 (aq) C 2 H 3 O 2 – (aq) + HCO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base H 3 PO 4 (aq) + OCl – (aq) H 2 PO 4 – (aq) + HOCl (aq) conjugate acid-base pairs Answers: question 18 (a) (b) (c)

acidbase conjugate baseconjugate acid HCO 3 – (aq) + S 2– (aq) HS – (aq) + CO 3 2– (aq) conjugate acid-base pairs baseacid conjugate acidconjugate base H 2 CO 3 (aq) + OH – (aq) HCO 3 – (aq) + H 2 O (l) conjugate acid-base pairs acidbase conjugate acidconjugate base H 3 O + (aq) + HSO 3 – (aq) H 2 O (l) + H 2 SO 3 (aq) conjugate acid-base pairs 8a) 8b) 11a) baseacid conjugate baseconjugate acid OH – (aq) + HSO 3 – (aq) H 2 O (l) + SO 3 2– (aq) conjugate acid-base pairs 11b) For more lessons, visit