1. Ammonia (NH3) Metal oxides Metal hydroxides
A BASE is a compound which reacts with an acid to form a salt and water only.
Examples of base:
Ammonia (NH3)
Metal oxides
Metal
hydroxides
16.1 Introducing bases and alkalis

2. Alkali Soluble Bases Only a few bases are soluble in water.
This means that all alkalis are bases, but not all bases are alkalis.
16.1 Introducing bases and alkalis

3. Bases e.g. CuO, Cu(OH)2 Alkalis e.g. NaOH
Figure All alkalis are bases, but not all bases are alkalis.
16.1 Introducing bases and alkalis

4. ammonia sodium hydroxide sodium hydroxide
COMMON ALKALIS IN DAILY LIFE
ammonia
sodium hydroxide
sodium hydroxide
Figure These household cleaners contain alkalis.
16.1 Introducing bases and alkalis

5. COMMON ALKALIS IN LABORATORY
Figure Alkalis commonly used in a laboratory.
16.1 Introducing bases and alkalis

6. How to prepare limewater?
16.1 Introducing bases and alkalis

7. Preparation of limewater
Calcium hydroxide is an alkali. It is a white solid, slightly soluble in water.
Limewater is a saturated aqueous solution of calcium hydroxide.
16.1 Introducing bases and alkalis

8. Preparation of limewater
1. Stirring solid calcium hydroxide with water for a long time.
2. Filtering the suspension.
3. The clear filtrate obtained is the limewater.
16.1 Introducing bases and alkalis

9. Electrical conductivity
16.2 CHARACTERISTICS AND CHEMICAL PROPERTIES OF AQUEOUS ALKALIS
Taste
Aqueous solutions of alkalis usually taste bitter.
(Never try to check this yourself!)
Feel
Dilute solutions of alkalis have a soapy feel.
Effect on litmus
They change red litmus paper to blue colour.
Electrical conductivity
Like acids, alkalis are electrolytes. They dissolve in water to form solutions that conduct electricity.

10. Chemical properties of alkalis
alkali + acidic substance salt + H2O(l) (neutralization)
(no heating)
e.g1. NaOH (aq) + HCl (aq)  NaCl (aq) + H2O (l)
e.g2. NH3 (aq) + HCl (aq)  NH4Cl (aq)
e.g3. 2NaOH (aq) + CO2 (g)  Na2CO3 (aq) + H2O (l)
e.g4. Ca(OH)2 (aq) + CO2 (g)  CaCO3 (s) + H2O (l)
limewater test
All ammonium compounds (NH4+) are soluble in water

11. Chemical properties of alkalis
B. alkali + NH4+ compound  salt + NH3(g) + H2O(l)
(heating)
e.g1. NaOH (aq) + NH4Cl(aq)  NaCl(aq) + NH3(g) + H2O(l)
e.g2. KOH (aq) + NH4Cl (aq)  KCl(aq) + NH3(g) + H2O(l)
NH3(g)+ NH4Cl(aq)  NH4Cl(aq) + NH3(g) + H2O(l)
Same reactants and products
This is not a possible reaction.
NH3(g) can turn red limus paper blue.

12. Chemical properties of alkalis
C. alkali + metal ions (aq)  hydroxides + salt
(no heating)
e.g1. 2NaOH (aq) + CuSO4 (aq)  Cu(OH)2(s) + Na2SO4(aq)
e.g2. NaOH(aq) + Cu(NO3)2 (aq) Cu(OH)2(s) + NaNO3(aq)
e.g3. 2H2O(l)+ 2NH3(aq)+ CuSO4(aq) Cu(OH)2(s)+ (NH4)2SO4(aq)
e.g4. NaOH(aq) + KNO3(aq) KOH(aq) + NaNO3(aq)
No ppt formed.
2OH- (aq) + Cu2+ (aq)  Cu(OH)2 (s)
2OH- (aq) + Cu2+ (aq)  Cu(OH)2 (s)

13. Metal Hydroxides Gp 1 hydroxides can dissolve in water(no ppt formed).
Hydroixdes of main group metals are white, while those are transition metals are coloured.
In excess NaOH:
Pb(OH)2 (s) , Al(OH)3 (s), Zn(OH)2 (s), are soluble in excess NaOH.

14. Water is important to alkalis (OH- ions)
e.g1 NaOH(aq)  Na+(aq) + OH-(aq)
e.g2
Strong alkali
NH3(aq) + H2O(l) NH4+(aq) + OH–(aq)
Weak alkali

15. A16.5
(a) (i) Fe2(SO4)3(aq) + 6NaOH(aq) 
2Fe(OH)3(s) + 3Na2SO4(aq)
(ii) Fe3+(aq) + 3OH-(aq)  Fe(OH)3(s)
(b) (i) Cu(NO3)2(aq) + 2KOH(aq)  Cu(OH)2(s) + 2KNO3(aq)
(ii) Cu2+(aq) + 2OH-(aq)  Cu(OH)2(s)

16. p32A Q14 Zinc dissolved/ colourless gas bubbles evolved.
Zn(s) + 2HCl (aq) ZnCl2(aq) + H2(g)
(b) Dirty green precipitates formed.
2NaOH (aq) + FeSO4 (aq)  Fe(OH)2(s) + Na2SO4(aq)
or 2OH- (aq) + Fe2+ (aq)  Fe(OH)2(s)

17. Alkalis (soluble bases)
Concept map
Complete the following concept map.
Bases
examples
metal oxides
____________
metal hydroxides
ammonia
Alkalis (soluble bases)
Insoluble bases
Concept map

18. Alkalis (soluble bases)
dissolve in water to give
properties
examples
OH-(aq)
KOH(aq)
NaOH(aq)
NH3(aq)
Ca(OH)2(aq)
Dilute alkalis
taste bitter
feel soapy
turn red litmus _______
conduct ____________
react with ______ to give salt and water
react with __________ oxides to give salts and water
react with ammonium compounds to give salt,__________ and water
react with ______ ions to form insoluble hydroxide (except K+ and Na+ ions)
blue
electricity
acids
Concentrated alkalis
_____________
non-metal
very corrosive
ammonia
metal
Concept map

19. How can we tell
a solution is
acidic, neutral
or alkaline?

20. All aqueous solution contain
17.1 pH AND INDICATORS
THE pH SCALE
H+(aq)
All aqueous solution contain
OH-(aq)

21. How can we tell a solution is acidic, neutral or alkaline?
It depends on the difference in H+(aq) concentration and
OH-(aq) concentration.
17.1 pH and indicators

22. Difference in H+(aq) and OH-(aq) concentration
H+(aq) concentration > OH-(aq) concentration
H+(aq) concentration = OH-(aq) concentration
H+(aq) concentration < OH-(aq) concentration
acidic
neutral
alkaline
Difference in H+(aq) and OH-(aq) concentration
Solution
Table Difference in H+(aq) and OH-(aq) concentration for acidic, neutral and alkaline solution.
H2O  H OH-
HCl  H+ + Cl-
17.1 pH and indicators

23. H+ (aq) concentration
express by
pH value
17.1 pH and indicators

24. pH scale : a measure of acidity and alkalinity Increasingly alkaline
Neutral
Increasingly acidic
Increasingly alkaline 7 14
On the pH scale:
An acidic solution has a pH value less than 7.
An neutral solution has a pH value of exactly 7.
An alkaline solution has a pH value greater than 7.
17.1 pH and indicators

25. (a) limewater (b) rainwater (c) soft drinks
Q17.1
what can you tell about the relationship between H+(aq) and OH-(aq) concentration of the following substances?
(a) limewater (b) rainwater (c) soft drinks
A17.1
(a) H+(aq) concentration < OH-(aq) concentration
(b) H+(aq) concentration > OH-(aq) concentration
(c) H+(aq) concentration > OH-(aq) concentration
17.1 pH and indicators

26. increasingly alkaline neutral acidic 1 2 3 4 5 6 7 8 9 10 11 12 13 141 2 3 4 5 6 7 8 9 10 11 12 13 14 pH
1 M NaOH
0.1 M NaOH
limewater
Na2CO3 solution
Milk of Magnesia,
household ammonia
soap solution
NaHCO3 solution
blood
rainwater
pure water
ordinary distilled water
(NH4)2SO4 solution
soft drink
orange juice
vinegar, 0.1 M CH3COOH
lemon juice
0.1 M HCl
1 M HCl
neutral
increasingly
alkaline
acidic

27. (a) Add a piece of magnesium ribbon to dilute hydrochloric acid.
Q17.3
State whether the pH value increases or decreases in each of the following cases:
(a) Add a piece of magnesium ribbon to dilute hydrochloric acid.
(b) Dissolve hydrogen chloride gas in water.
A17.3
(a) Increases
(b) Decreases
17.1 pH and indicators

28. COMMON ACID-BASE INDICATORS
An acid-base indicator is a special dye added to the solution to be tested.
Figure Three common acid-base indicators.
17.1 pH and indicators

29. Different acid-base indicators show different colours in different pH ranges.
Methyl orange
Indicator
pH scale
Litmus
red
purple
blue
orange
yellow
3.1
4.4 5 8
Phenolphthalein
very pale
pink
colourless
8.3 10 1 2 3 4 6 7 9 11 12 13 14
Figure Different colours of acid-base indicators in different pH ranges.
17.1 pH and indicators

30. pH meter Universal indicator
MEASURING pH OF A SOLUTION
pH meter
Measuring
pH value
Universal indicator
17.1 pH and indicators

31. A mixture of several indicators
Universal indicator
A mixture of several indicators
Gives different colours in different pH ranges
Available as a solution or
paper (pH paper)
17.1 pH and indicators

32. Figure 17.4 pH paper and pH colour chart.
17.1 pH and indicators

33. universal indicator solution
Figure Finding the pH value of a solution by universal indicator solution. Put the solution in front of a piece of white paper to see the colour easily.
17.1 pH and indicators

34. Do not dip the pH paper into the solution to be tested! Why?
Q17.4
Do not dip the pH paper into the solution to be tested! Why?
A17.4
The dyes on the pH paper may go into the solution and contaminate it.
17.1 pH and indicators

35. pH meter To measure pH values accurately, use a pH meter. electrodes
17.1 pH and indicators

36. Normal functioning of body fluids
IMPORTANCE OF pH
Keeping a constant pH value is important in many cases, for example:
Normal functioning of body fluids
Water supply
Food production
17.1 pH and indicators