Acid

1
Acids
and
Bases
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
Observations
Usually, but not always
HCl(aq)
NaOH(aq)
Sour
Bitter
Taste
Not slippery
Slippery
Feel (choose slippery or not slippery)
1
14
pH ( from the key)
Red
Blue
Litmus (blue or red)
Cloudy/ white
Pink
Phenolphthalein
Yellow
Blue
Bromothymol
Bubbles
NR
Magnesium
Bubbles
NR
Baking soda
4
pH

• There are many ways to consider acids and bases.
  One of these is pH. Read pg. 368-70.
• 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
  107

5
Calculations with pH

• Q What is the pH if H 6.3 x 105?
• pH log H
• (6.3, exp or EE, 5, /-, log,
  /-)
• (-, log, 6.3, exp or EE, -,
  5)

Ans 4.2
Q What is the H if pH 7.4? H 10pH
mol/L (10, xy, 7.4, /-,
) (10, , -, 7.4, )
3.98 x 108 M
Try questions 2 and 6 (a-b) on page 375
6
Pg. 375

• 2 a) pH log H log 1x108 8.0
• b) pH log H log 1x107 7.0
• c) pH log H log 2.5x106 5.60
• d) pH log H log 1.3x104 3.89
• 6 a) H 10pH 105.4 4 x 106 mol/L
• b) H 10pH 105.72 1.9 x 106 mol/L

7
Historical views on acids

• O (e.g. H2SO4) was originally thought to cause
  acidic properties. Later, H was implicated, but
  it was still not clear why CH4 was neutral.
• Arrhenius made the revolutionary suggestion that
  some solutions contain ions that acids produce
  H3O (hydronium) ions in solution.

• The more recent Bronsted-Lowry concept is that
  acids are H (proton) donors and bases are proton
  acceptors

8
The Bronsted-Lowry concept

• In this idea, the ionization of an acid by water
  is just one example of an acid-base reaction.

acid
base
conjugate acid
conjugate base
conjugate acid-base pairs

• 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.

9
Practice problems
Identify the acid, base, conjugate acid,
conjugate base, and conjugate acid-base pairs
HC2H3O2(aq) H2O(l) ? C2H3O2(aq) H3O(aq)
acid
base
conjugate acid
conjugate base
conjugate acid-base pairs
OH (aq) HCO3(aq) ? CO32(aq) H2O(l)
acid
base
conjugate acid
conjugate base
conjugate acid-base pairs

• Reference pg. 386 387
• Try Q18 (p389), Q 8 11 (p392) do as above

10
Answers question 18
HF(aq) SO32(aq) ? F(aq) HSO3(aq)
(a)
acid
base
conjugate acid
conjugate base
conjugate acid-base pairs
(b)
CO32(aq) HC2H3O2(aq) ? C2H3O2(aq) HCO3(aq)
acid
base
conjugate acid
conjugate base
conjugate acid-base pairs
(c)
H3PO4(aq) OCl (aq) ? H2PO4(aq) HOCl(aq)
acid
base
conjugate acid
conjugate base
conjugate acid-base pairs
11
HCO3(aq) S2(aq) ? HS(aq) CO32(aq)
8a)
acid
base
conjugate base
conjugate acid
conjugate acid-base pairs
8b)
H2CO3(aq) OH (aq) ? HCO3(aq) H2O(l)
base
acid
conjugate acid
conjugate base
conjugate acid-base pairs
11a)
H3O(aq) HSO3(aq) ? H2O(l) H2SO3(aq)
acid
base
conjugate acid
conjugate base
conjugate acid-base pairs
11b)
OH (aq) HSO3(aq) ? H2O(l) SO32(aq)
base
acid
conjugate base
conjugate acid
conjugate acid-base pairs
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