This is a summary of the topic "Acids and bases" in the GCE O levels subject: Chemistry. Students taking either the combined science (chemistry/physics) or pure chemistry will find this useful. These slides are prepared according to the learning outcomes required by the examinations board.

1. ACIDS AND BASES

2. WHAT IS AN ACID?
Definition: An acid is a substance that produces hydrogen ions, H+, in aqueous solution.

3. ACIDS
Acid Formula Ions produced in aqueous
solution
hydrochloric acid HCl H+(aq) Cl-(aq)
nitric acid HNO3 H+(aq) NO3
-(aq)
sulfuric acid H2SO4 H+(aq) SO4
2-(aq)

4. ACIDS
hydrochloric acid  hydrogen ion + chloride ion
HCl(aq)  H+(aq) + Cl-(aq)
sulfuric acid  hydrogen ion + sulfate ion
H2SO4(aq)  2H+(aq) + SO4
2-(aq)
The hydrogen ions produced gives the properties of acids.

5. PROPERTIES OF ACIDS
1. Acids have a sour taste.
2. Acids dissolved in water can conduct electricity.
3. Acids turns damp blue litmus red.

6. CHEMICAL REACTIONS OF ACIDS
General equations:
1. metal + acid  salt + hydrogen
2. metal carbonate + acid  salt + water + carbon dioxide
3. metal oxide/metal hydroxide + acid  salt + water

7. CHEMICAL REACTIONS OF ACIDS
metal + acid  salt + hydrogen
magnesium + dilute sulfuric acid  magnesium sulfate + hydrogen
Mg(s) + H2SO4(aq)  MgSO4(aq) + H2(g)

8. CHEMICAL REACTIONS OF ACIDS
metal carbonate + acid  salt + water + carbon dioxide
calcium carbonate + dilute hydrochloric acid  calcium chloride + water + carbon dioxide
CaCO3(s) + 2HCl(aq)  CaCl2(aq) + H2)(l) + CO2(g)

9. CHEMICAL REACTIONS OF ACIDS
metal oxide + acid  salt + water
zinc oxide + dilute sulfuric acid  zinc sulfate + water
ZnO(s) + H2SO4(aq) ZnSO4(aq) + H2O(l)

10. CHEMICAL REACTIONS OF ACIDS
metal hydroxide + acid  salt + water
zinc hydroxide + dilute nitric acid  zinc nitrate + water
Zn(OH)2(s) + 2HNO3(aq)  Zn(NO3)2(aq) + 2H2O(l)

11. USES OF ACIDS
Sulfuric acid is one of the most widely used acids. It is used to:
1. Manufacture fertilizers.
2. Manufacture detergents.
3. Produce car batteries.

12. WHAT IS A BASE?
Definition: A base is any metal oxide or hydroxide that reacts with an acid to produce a salt and
water only. Most bases are insoluble.
A base is a combination of a metal with either oxide ions, O2- or hydroxide ions, OH-.

13. BASES
Base Formula
sodium oxide Na2O
zinc oxide ZnO
copper (II) oxide CuO
magnesium hydroxide Mg(OH)2
aluminum hydroxide Al(OH)3

14. CHEMICAL REACTIONS OF BASES
base + acid  salt + water
copper(II) oxide + dilute sulfuric acid  copper(II) sulfate + water
CuO(s) + H2SO4(aq)  CuSO4(aq) + H2O(l)

15. ALKALIS: A SPECIAL CLASS OF BASE
Definition: An alkali is a substance that produces hydroxide ions, OH-, in aqueous solution. It is a
base that is soluble in water.

16. ALKALIS: A SPECIAL CLASS OF BASE
Alkali Formula Ions produced in aqueous
solution
sodium hydroxide NaOH Na+(aq) OH-(aq)
potassium hydroxide KOH K+(aq) OH-(aq)
calcium hydroxide Ca(OH)2 Ca2+(aq) OH-(aq)
barium hydroxide Ba(OH)2 Ba2+(aq) OH-(aq)

17. ALKALIS
sodium hydroxide  sodium ion + hydroxide ion
NaOH(aq)  Na+(aq) + OH-(aq)
calcium hydroxide  calcium ion + hydroxide ion
Ca(OH)2(aq)  Ca2+(aq) + 2OH-(aq)

18. PROPERTIES OF ALKALIS
1. Alkalis have a bitter taste and feel soapy.
2. Alkalis turn damp red litmus paper blue.

19. CHEMICAL REACTIONS OF ALKALIS
General equations:
1. Alkalis react with acids to form a salt and water only.
2. Alkalis, when heated with ammonium salts, give off ammonia gas.
3. Alkalis react with a solution of one metal salt to give another metal salt and metal hydroxide.

20. CHEMICAL REACTIONS OF ALKALIS
alkali + acid  salt + water
sodium hydroxide + dilute hydrochloric acid  sodium chloride +water
NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l)
This process is neutralization as only a salt and water is produced.
The ionic equation for this: H+(aq) + OH-(aq)  H2O(l)

21. CHEMICAL REACTIONS OF ALKALIS
alkali + ammonium salt  salt + water + ammonia
calcium hydroxide + ammonium chloride  calcium chloride + water + ammonia
Ca(OH)2(aq) + 2NH4Cl(s)  CaCl2(aq) + 2H2O(l) + 2NH3(g)

22. CHEMICAL REACTIONS OF ALKALIS
alkali (containing metal A) + salt (of metal B)  salt (of metal A) + metal hydroxide (of metal B)
sodium hydroxide + iron(II) sulfate  sodium sulfate + iron(II) hydroxide
2NaOH(aq) + FeSO4(aq)  Na2SO4(aq) + Fe(OH)2(s)

23. USES OF BASES AND ALKALIS
1. Magnesium oxide is used as antacid for relieving gastric pain and for making refractory
bricks.
2. Sodium hydroxide and potassium hydroxide are used in the preparation of soap.
3. Calcium hydroxide (lime) is used to reduced acidity in soil.
4. Ammonia solution is used to make fertilizers.

24. STRONG AND WEAK ACIDS
The term strength refers to how easily an acid or an alkali ionizes when dissolved in water. We
can explain the strength of acids in terms of their extent of ionization.

25. STRONG AND WEAK ACIDS
A strong acid is an acid that is completely ionized in aqueous solution.
HCl(aq)  H+(aq) + Cl-(aq)
A weak acid is an acid that is only partially ionized in aqueous solution.
CH3COOH(aq) ⇌ CH3COO-(aq) + H+(aq)
The sign “⇌” indicates partial ionization.

26. THE PH SCALE
The strength of an acid or alkali can be shown using the pH scale.
The pH of a solution is related to the concentration of hydrogen ions or hydroxide ions present in
a solution. An acid with a lower pH value is more acidic as it has a higher concentration of
hydrogen ions. A alkaline solution with a higher pH value is more alkaline as it has a higher
concentration of hydroxide ions.

27. THE PH SCALE
Universal Indicator
The pH value of a solution can be determined by using Universal Indicator.

28. OTHER INDICATORS
Indicator Colour in acidic solution pH range at which
indicator changes colour
Colour in alkaline
solution
methyl orange red 3 - 5 yellow
screened methyl orange violet 3 - 5 green
litmus red 5 - 8 blue
bromothymol blue yellow 6 - 8 blue
phenolphthalein colourless 8 - 10 pink

29. IMPORTANCE OF PH
Our blood is slightly alkaline and has a pH of around 7.4. Any injection given must have a pH of
almost 7.4. If the pH of our blood changes to much, it could cause death.
It is important to control the pH of soil because this affects the growth and development of
plants. Most plants grow best when the soil is neutral or slightly acidic. We can add chemicals to
control the pH of soil. Soil that are too acidic can be treated with bases such as quicklme
(calcium oxide) or slaked lime (calcium hydroxide).

30. TYPES OF OXIDES
Many acids and alkalis are formed by dissolving oxides in water. There are four types of oxides:
1. Acidic oxides
2. Basic oxides
3. Amphoteric oxides
4. Neutral oxides

31. ACIDIC OXIDES
Most oxides of non-metals are acidic oxides and they dissolve in water to form acids.
sulfur dioxide + water  sulfurous acid
SO2(g) + H2O(l)  H2SO3(aq)

32. ACIDIC OXIDES
Acidic oxide Formula Physical states Acid produced in water
carbon dioxide CO2 gas carbonic acid H2CO3
sulfur trioxide SO3 gas sulfuric acid H2SO4
phosphorous(V)
oxide
P4H10 solid phosphoric acid H3PO4

33. ACIDIC OXIDES
Acidic oxides do not react with acids, but they react with alkalis to form a salt and water.
sulfur dioxide + sodium hydroxide  sodium sulfite + water
SO2(g)n+ 2NaOH(aq)  Na2SO3(aq) + H2O(l)

34. BASIC OXIDES
Most oxides of metals are basic oxides and they are insoluble. Some oxides, such as sodium
oxide and potassium oxide dissolve readily in water to form alkalis.

35. BASIC OXIDES
Basic oxides are solids at room temperature and they react with acids to form a salt and water.
calcium oxide + nitric acid  calcium nitrate + water
CaO(s) + 2HNO3(aq)  Ca(NO3)2(aq) + H2O(l)

36. AMPHOTERIC OXIDES
Amphoteric oxides are metallic oxides that react with both acids and bases to form salt and
water.
Zinc oxide is an example of an amphoteric oxide. It is able to react with both hydrochloric acid
and sodium hydroxide.

37. AMPHOTERIC OXIDES
hydrochloric acid + zinc oxide  zinc chloride + water
2HCl(aq) + ZnO(s)  ZnCl2(aq) + H2O(l)
sodium hydroxide + zinc oxide  sodium zincate + water
2NaOH(aq) + ZnO(s)  Na2ZnO2(aq) + H2O(l)

38. AMPHOTERIC OXIDES
Amphoteric oxide Formula
aluminium oxide Al2O3
lead(II) oxide PbO

39. NEUTRAL OXIDES
Some non-metals form oxides that are neither basic or acidic in nature. They are called neutral
oxides and they are insoluble in water.

40. NEUTRAL OXIDES
Neutral oxides Formula
water H2O
carbon monoxide CO
nitric oxide NO

41. HOW TO IDENTIFY AN UNKNOWN
OXIDE?
Unknown oxide
Reacts with acid
Basic or
amphoteric oxide
Reacts with alkali
Amphoteric
oxide
Does not react
with alkali
Basic oxide
Does not react
with acid
Acidic or neutral
oxide
Reacts with alkali Acidic oxide
Does not react
with alkali
Neutral oxide

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