1. iGCSE chemistry Section 4 lesson 1

2. The iGCSE Chemistry course
Content
The iGCSE Chemistry course
Section 1 Principles of Chemistry
Section 2 Chemistry of the Elements
Section 3 Organic Chemistry
Section 4 Physical Chemistry
Section 5 Chemistry in Society

3. Section 4 Physical Chemistry Acids, alkalis and salts Energetics
Content
Section 4
Physical Chemistry
Acids, alkalis and salts
Energetics
Rates of reaction
Equilibria

4. Lesson 1 a) Acids, alkalis and salts
4.1 describe the use of the indicators litmus, phenolphthalein and methyl orange to distinguish between acidic and alkaline solutions
4.2 understand how the pH scale, from 0–14, can be used to classify solutions as strongly acidic, weakly acidic, neutral, weakly alkaline or strongly alkaline
4.3 describe the use of universal indicator to measure the approximate pH value of a solution
4.4 define acids as sources of hydrogen ions, H+, and alkalis as sources of hydroxide ions, OH¯
4.5 predict the products of reactions between dilute hydrochloric, nitric and sulfuric acids; and metals, metal oxides and metal carbonates (excluding the reactions between nitric acid and metals)
4.6 understand the general rules for predicting the solubility of salts in water:
i all common sodium, potassium and ammonium salts are soluble
ii all nitrates are soluble
iii common chlorides are soluble, except silver chloride
iv common sulfates are soluble, except those of barium and calcium
v common carbonates are insoluble, except those of sodium, potassium and ammonium
4.7 describe experiments to prepare soluble salts from acids
4.8 describe experiments to prepare insoluble salts using precipitation reactions
4.9 describe experiments to carry out acid-alkali titrations.
Lesson 1
a) Acids, alkalis and salts

5. pH scale and indicators
The pH scale is a measure of how acidic or alkaline a solution is.

6. pH scale and indicators
The pH scale is a measure of how acidic or alkaline a solution is.
ACIDIC
neutral
ALKALINE
Very Slightly
Slightly Very 1 2 3 4 5 6 7 8 9 10 11 12 13 14

7. pH scale and indicators
The pH scale is a measure of how acidic or alkaline a solution is.
ACIDIC
neutral
ALKALINE
Very Slightly
Slightly Very 1 2 3 4 5 6 7 8 9 10 11 12 13 14
A substance forms an aqueous solution when it dissolves in water. Water itself is neutral.
When substances dissolve in water, they dissociate into individual ions.

8. pH scale and indicators
Water, H2O
H+(aq) OH-(aq)
hydrogen ion hydroxide ion
acid alkali

9. pH scale and indicators
Indicators are special dyes that change colour according to whether they are in acidic, alkaline or neutral solutions.

10. pH scale and indicators
Indicators are special dyes that change colour according to whether they are in acidic, alkaline or neutral solutions.
Three common indicators are:
Litmus
Phenolphthalein
Methyl Orange

11. pH scale and indicators
Litmus
ACIDIC
neutral
ALKALINE
Very Slightly
Slightly Very 1 2 3 4 5 6 7 8 9 10 11 12 13 14
5.0
8.0

12. pH scale and indicators
Methyl Orange
ACIDIC
neutral
ALKALINE
Very Slightly
Slightly Very 1 2 3 4 5 6 7 8 9 10 11 12 13 14
4.4
6.2

13. pH scale and indicators
Phenolphthalein
ACIDIC
neutral
ALKALINE
Very Slightly
Slightly Very 1 2 3 4 5 6 7 8 9 10 11 12 13 14
8.3 10

14. pH scale and indicators
Universal indicator is a mixture of dyes, and shows a complete colour range across the pH scale.

15. Common acids and alkalis
Name
Formula
Hydrochloric acid
HCl
Sulphuric acid
H2SO4
Nitric acid
HNO3

16. Common acids and alkalis
Name
Formula
Hydrochloric acid
HCl
Sulphuric acid
H2SO4
Nitric acid
HNO3
ALKALIS
Name
Formula
Sodium hydroxide
NaOH
Potassium hydroxide
KOH
Calcium hydroxide
Ca(OH)2

17. Acid + Base  Salt + Water
Salt formation
When acids and alkalis react together, salts are formed.
The general equation is:
Acid Base  Salt Water

18. Acid + Base  Salt + Water
Salt formation
When acids and alkalis react together, salts are formed.
The general equation is:
Acid Base  Salt Water
This is known as a neutralisation reaction because the products are neutral.

19. Salt formation
Salts consist of two parts – a metal part, and the non-metal ion from the acid.
Acid
Ions in solution
Salts formed
Hydrochloric acid
H+ Cl-
chlorides
Sulphuric acid
2H+ SO42-
sulphates
Nitric acid
H+ NO3-
nitrates

20. Salt formation Examples of salts Salt Formula Metal ion Non-metal ion
Copper sulphate
CuSO4
Cu2+
SO42-
Sodium chloride
NaCl
Na+
Cl-
Potassium nitrate
KNO3 K+
NO3-
Calcium sulphate
CaSO4
Ca2+

21. Acid + Metal  Salt + Hydrogen
Reactions of salts
Acids + Metals
Acid Metal  Salt Hydrogen

22. Reactions of salts Mg + 2HCl  MgCl2 + H2 Acids + Metals
Acid Metal  Salt Hydrogen
Magnesium + Hydrochloric  Magnesium Hydrogen
Acid chloride
Mg HCl  MgCl H2

23. Have you got that? Are you really sure? Let’s try a few examples.
Reactions of salts
Acids + Metals
Have you got that? Are you really sure? Let’s try a few examples.

24. Reactions of salts Acids + Metals Magnesium + Sulphuric Acid 
Iron + Hydrochloric Acid 
Lead Sulphuric Acid 

25. Reactions of salts Acids + Metals
Magnesium + Sulphuric Acid  Magnesium sulphate Hydrogen
Iron + Hydrochloric Acid  Iron chloride + Hydrogen
Lead Sulphuric Acid  Lead sulphate + Hydrogen

26. Acid + Metal oxide  Salt + Water
Reactions of salts
Acids + Metal oxides
Acid Metal oxide  Salt Water

27. Reactions of salts CuO + H2SO4  CuSO4+ H2O Acids + Metal oxides
Acid Metal oxide  Salt Water
Copper + Sulphuric  Copper + Water
oxide Acid sulphate
CuO + H2SO4  CuSO4+ H2O

28. Reactions of salts
Acids + Metal oxides
Have you got that? Are you really, really sure? Let’s try a few more examples.

29. Reactions of salts Acids + Metal oxide Magnesium + Hydrochloric Acid 
Iron + Sulphuric Acid 
oxide
Lead Hydrochloric Acid 
oxide

30. Reactions of salts Acids + Metal oxide
Magnesium + Hydrochloric Acid  Magnesium + Water
oxide chloride
Iron + Sulphuric Acid  Iron sulphate + Water
oxide
Lead Hydrochloric Acid  Lead chloride + Water
oxide

31. Acid + Metal  Salt + Carbon + Water
Reactions of salts
Acids + Metal carbonate
Acid + Metal  Salt + Carbon + Water
carbonate dioxide

32. Reactions of salts CuCO3 + 2HCl  CuCl2 + CO2 + H2O
Acids + Metal carbonate
Acid + Metal  Salt + Carbon + Water
carbonate dioxide
Copper + Hydrochloric  Copper + Carbon Water
Carbonate acid chloride dioxide
CuCO3 + 2HCl  CuCl2 + CO2 + H2O

33. Guess what? That’s right, no more examples!
Reactions of salts
Acids + Metal carbonate
Guess what? That’s right, no more examples!

34. Solubility of salts
If a substance is soluble, then this means that it will dissolve in a solvent.

35. Solubility of salts
If a substance is soluble, then this means that it will dissolve in a solvent.
The most common solvent you will come across is WATER.

36. Solute (the solid) + Solvent (water)
Solubility of salts
If a substance is soluble, then this means that it will dissolve in a solvent.
The most common solvent you will come across is WATER.
Solute (the solid) + Solvent (water)
 Solution (aqueous)

37. Solubility of salts
There’s no easy way around this – you’ve just got to learn the relative solubility of salts!

38. All ammonium, potassium and sodium salts are soluble in water.
Solubility of salts
All ammonium, potassium and sodium salts are soluble in water.

39. Solubility of salts
All ammonium, potassium and sodium salts are soluble in water.
All nitrates are soluble in water

40. Solubility of salts
All ammonium, potassium and sodium salts are soluble in water.
Most chlorides are soluble in water (except lead and silver). PbCl2 is soluble in hot water.
All nitrates are soluble in water

41. Solubility of salts
All ammonium, potassium and sodium salts are soluble in water.
Most sulphates are soluble in water (except barium, calcium and lead)
Most chlorides are soluble in water (except lead and silver). PbCl2 is soluble in hot water.
All nitrates are soluble in water

42. Solubility of salts
Most carbonates are insoluble in water (except sodium, potassium and ammonium)
All ammonium, potassium and sodium salts are soluble in water.
Most sulphates are soluble in water (except barium, calcium and lead)
Most chlorides are soluble in water (except lead and silver). PbCl2 is soluble in hot water.
All nitrates are soluble in water

43. Preparing insoluble salts using precipitation reactions
Preparing soluble salts from acids
Carrying out acid-alkali titrations

44. Preparing soluble salts from acids
Eg. the preparation of sodium chloride by neutralization

45. Preparing soluble salts from acids
Eg. the preparation of sodium chloride by neutralization
Dilute sodium hydroxide
+ indicator solution
Dilute hydrochloric acid

46. Preparing soluble salts from acids
Eg. the preparation of sodium chloride by neutralization
Filtrate
Decolourising
charcoal
Evaporating basin

47. Preparing soluble salts from acids
Eg. the preparation of sodium chloride by neutralization
Crystals of sodium chloride forming)
Acid + Alkali 
Salt + Water
Filtrate
Steam
HCl(aq) + NaOH(aq) 
NaCl(aq) + Water(l)
Water bath
Bunsen burner

48. Preparing insoluble salts using precipitation reactions
Eg. the preparation of lead iodide

49. Preparing insoluble salts using precipitation reactions
Eg. the preparation of lead iodide
Yellow precipitate of lead iodide
Lead nitrate
Potassium iodide

50. Preparing insoluble salts using precipitation reactions
Eg. the preparation of lead iodide
Filter to separate the precipitate. Wash with distilled water and dry to get the pure product.
Lead iodide

51. Preparing insoluble salts using precipitation reactions
Eg. the preparation of lead iodide
Filter to separate the precipitate. Wash with distilled water and dry to get the pure product.
Salt + Salt  Insoluble + Soluble
salt salt
Lead + Potassium  Lead Potassium
nitrate iodide iodide nitrate
Pb(NO3)2(aq) + 2KI(aq)  PbI(s) + 2KNO3(aq)
Lead iodide

52. Acid – Alkali Titrations
A titration is a very accurate way of adding an acid to an alkali to get a salt.

53. Acid – Alkali Titrations
To carry out an acid-alkali titration we need the right bits of kit.
Conical flask

54. Acid – Alkali Titrations
To carry out an acid-alkali titration we need the right bits of kit.
Pipette

55. Acid – Alkali Titrations
To carry out an acid-alkali titration we need the right bits of kit.
Burette

56. Acid – Alkali Titrations
Stage 1
meniscus
Dilute sodium hydroxide (NaOH) solution is sucked up into a pipette using a pipette filler. The pipette contains exactly 25.0cm3 of solution when the bottom of the meniscus is level with the pipette mark. The sodium hydroxide solution is then released in to the conical flask.

57. Acid – Alkali Titrations
Stage 1
meniscus
Dilute sodium hydroxide (NaOH) solution is sucked up into a pipette using a pipette filler. The pipette contains exactly 25.0cm3 of solution when the bottom of the meniscus is level with the pipette mark. The sodium hydroxide solution is then released in to the conical flask.

58. Acid – Alkali Titrations
Stage 2
Two or three drops of an acid-alkali indicator such as litmus solution are added to the sodium hydroxide solution using a teat pipette. The alkali turns the litmus blue.

59. Acid – Alkali Titrations
Stage 3
The burette is filled with dilute hydrochloric acid to the zero reading. (Again, look for the meniscus)

60. Acid – Alkali Titrations
Stage 4
The conical flask is placed on a white tile beneath the burette. Acid is added from the burette until the colour of the solution turns from blue to red. The point at which the colour changes is called the end-point. At this stage the conical flask only contains salt and water.

61. Acid – Alkali Titrations
Stage 4
The conical flask is placed on a white tile beneath the burette. Acid is added from the burette until the colour of the solution turns from blue to red. The point at which the colour changes is called the end-point. At this stage the conical flask only contains salt and water.
At the end-point the volume of acid added can be measured by reading off the volume used in the burette – this is the titre

62. Preparing insoluble salts using precipitation reactions
Preparing soluble salts from acids
Carrying out acid-alkali titrations

63. Preparing insoluble salts using precipitation reactions
Preparing soluble salts from acids
Carrying out acid-alkali titrations

64. Preparing insoluble salts using precipitation reactions
Preparing soluble salts from acids
Carrying out acid-alkali titrations

65. End of Section 4 Lesson 1 In this lesson we have covered:
pH scale and indicators
Common acids and alkalis
Salt formation and reactions
Preparing salts