LARUTAN ASAM DAN BASA

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
Taste
Feel (choose slippery
or not slippery)
pH (# from the key)
Litmus (blue or red)
NaOH(aq)
Bitter
HCl(aq)
Sour
Slippery
Not slippery
14
Blue
1
Red
*Cloudy/
white
*Yellow
Bubbles
Bubbles
Phenolphthalein
*Pink
Bromothymol
Magnesium
Baking soda
*Blue
NR
NR

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 10–7

5. Calculations with pH
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‟)
Ans: 4.2
Q: What is the [H+] if pH = 7.4?
[H+] = 10–pH mol/L
(‟10‟, „xy‟, „7.4‟, „+/-‟, „=„)
3.98 x 10–8 M
(‟10‟, „^‟, „-‟, „7.4‟, „=„)
Try questions 2 and 6 (a-b) on page 375

6. Pg. 375
2 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] = 3.89
6 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

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.
Ionization
+
H
H
HO
+ Cl
Cl H + O
H
H
• 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.
H
Cl H
acid
+
O
H
base
+
H
HO
+
Cl
H
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 base conjugate acid
conjugate acid-base pairs
OH –(aq) + HCO3–(aq)  CO32–(aq) + H2O(l)
base
acid
conjugate base conjugate acid
conjugate acid-base pairs
• Reference: pg. 386 – 387
• Try Q18 (p389), Q 8 & 11 (p392): do as above

10. Answers: question 18
(a) HF(aq) + SO32–(aq)  F–(aq) + HSO3–(aq)
acid
base
conjugate base conjugate acid
(b)
conjugate acid-base pairs
CO32–(aq) + HC2H3O2(aq)  C2H3O2–(aq) + HCO3–(aq)
base
acid
conjugate base conjugate acid
(c)
conjugate acid-base pairs
H3PO4(aq) + OCl –(aq)  H2PO4–(aq) + HOCl(aq)
acid
base
conjugate base conjugate acid
conjugate acid-base pairs

11. 8a) HCO3–(aq) + S2–(aq)  HS–(aq) + CO32–(aq)
acid
base conjugate acid conjugate base
conjugate acid-base pairs
8b) H2CO3(aq) + OH –(aq)  HCO3–(aq) + H2O(l)
acid
base conjugate base conjugate acid
conjugate acid-base pairs
11a) H3O+(aq) + HSO3–(aq)  H2O(l) + H2SO3(aq)
acid
base
conjugate base conjugate acid
conjugate acid-base pairs
11b) OH –(aq) + HSO3–(aq)  H2O(l) + SO32–(aq)
base
acid conjugate acid conjugate base
conjugate acid-base pairs
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