Acids and bases

1. Acids & Bases

2. Our Goals for today
 To determine the difference between Acids &
Bases
 To describe the characteristic reactions of acids
with metals, bases (including alkalis) and
carbonates
 To describe and explain the importance of
controlling acidity in the environment (air, water,
and soil)
 To perform an experiment dealing with Acids &
Bases

3. What is the pH scale?
 The pH scale
measures how
acidic
or basic
a solution is.

4. Identifying Acids and Bases
Acidshave a pH from 0-7
Lower pH value indicates a stronger acid.
Bases have a pH from 7-14
Higher pH value indicates a stronger base.

5. Definitions of Acids and Bases
 An acid is a substance that breaks into [H+] ions in
an aqueous solution.
 A Base (alkaline) is a substance that breaks into
[OH–] ions in an aqueous solution.
 Note: aqueous solution is any solution where H2O
is the solvent.

6. Properties of Acids
 Taste sour
 pH < 7
 Acids affect indicators:
 Acids turn blue litmus to red
 Acids turn methyl orange to red
 Acids neutralize bases producing a salt and water
 Acids react with active metals to produce hydrogen
 Acids react with carbonates to produce a salt,
water and CO2
 Proton donors (Proton = H+ = hydrogen ion)

7. The Reactions of Acids
1. With Bases
2. With Alkali
sulphuric acid + copper(II) oxide 
copper(II)
sulphate
+ water
H2SO4 (aq) + CuO (s)  CuSO4 (aq) + H2O (l)
Acid + metal oxide  metal salt + water
sulphuric acid +
magnesium
hydroxide

magnesium
sulphate
+ water
H2SO4 (aq) + Mg(OH)2 (aq)  MgSO4 (aq) + 2 H2O (l)
Acid + metal hydroxide  metal salt + water

8. The Reactions of Acids
3. With Metals
Other examples:
sulphuric acid + magnesium 
magnesium
sulphate
+ hydrogen
H2SO4 (aq) + mg (s)  MgSO4 (aq) + H2 (g)
Acid + metal  metal salt + hydrogen

9. The Reactions of Acids
4. With Carbonates
Other examples:
hydrochloric
acid
+
calcium
carbonate

calcium
chloride
+ water +
carbon
dioxide
2 HCl (aq) + CaCO3 (s)  CaCl2 (aq) + H2O (l) + CO2 (g)
Acid +
metal
carbonate
 metal salt + water +
carbon
dioxide

10. Properties of Bases
 Taste bitter
 pH > 7
 Bases affect indicators:
 Acids turn red litmus to blue
 Acids turn methyl orange to
 Bases neutralize acids producing a salt and water
 Proton acceptors (Proton = H+ = hydrogen ion)
 It feels slippery

11. Neutralization Reaction
 Exothermic: it gives out heat  temp. of sol. ↑
 Neutralization with ammonia
A solution of ammonia in water is alkaline.
NH3 + H20  NH4
+ + OH–
OH– + H+ of acid
 Complete neutralization reaction: use indicator
PHENOLPHTHALEIN
Alkaline Neutral

12. Everyday Life
 Soil: plants will grow best with the pH close to 7.
⁞ Otherwise, we will lack of plant products
(vegetables, fruits, nuts, beans, etc) to eat.
⁞ It disturbs ecosystem of the river.
⁞ Quicklime (calcium oxide), Slaked lime (calcium hydroxide),
limestone (calcium carbonate)
 Water: factory waste. Liquid waste (often acid) reaches rivers.
⁞ It kills fish and other living things.
⁞ It disturbs ecosystem of the river.
⁞ Slaked lime (calcium hydroxide)

13. Everyday Life
 Air: acid rain.
 Waste gases from our daily activities (such as gases from our
electricity, gases from our transportations, burns from the
factory) go into the air.
 Carbon dioxide + water from the rainfall  carbonic acid
CO2 (g) + H2O (l)  H2CO3 (aq)
 Sulphur dioxide and oxides of nitrogen
sulphur dioxide
+ Air + Water
 Sulphuric acid
oxides of nitrogen  Nitric acid

14. Everyday Life
 Air: acid rain.
⁞ It destroys:
 buildings, concrete, cement (calcium carbonate)
 Bridges, iron railings, car bodies
 Plants
⁞ It dissolves aluminium from minerals in rocks and soil.
⁞ It carries it into the river
⁞ < fish
⁞ Slaked lime (calcium hydroxide)

15. Did we Miss something??
 What happens when the pH of a substance is 7?
 Ans: A pH level of 7 indicates a Neutral Substance i.e:
Water!
What else besides water?