1. Acids and Bases

2. Acids are substances that turn blue litmus red.
Examples of Acids found in household items: oranges, lemons, vinegar!

3. Strong acids..

4. Bases are substances that turn red litmus indicator blue.
Examples of bases In the household: soap, toothpaste

5. Strong bases…

6. When an acid is mixed with a base they react with each other form a salt and water. This is called a neutralisation reaction.
Acid + Base Salt + Water

7. Uses of neutralisation reactions: 1. Treating wasp stings
A wasp sting is basic.
Vinegar, an acid, can be used to treat
a wasp sting because when they react with each other a neutralisation reaction happens

8. Uses of neutralisation reactions: 2. Neutralising soil
Many plants do not grow
well in acidic soil.
Farmers often add lime (a base) to acidic soil to make their plants grow better.

9. Arrhenius – a new way to think about acids and bases

10. Arrhenius acids and bases
An Arrhenius acid is a substance that dissociates in water, forming hydrogen ions
HA H+ + A-

11. Arrhenius said… HA H+ + A-
A strong acid is one which fully dissociates in water
A weak acid is one which is only slightly dissociates in water
HA H+ + A-

12. Arrhenius acids and bases
An Arrhenius base is a substance that dissociates in water, forming hydroxide ions
MOH OH- + M+

13. Arrhenius said… MOH OH- + M+
A strong base is one which fully dissociates in water
A weak base is one which is only slightly dissociates in water
MOH OH- + M+

14. Bronsted Lowry Theory of acids and bases
An acid is a proton donor
A base is a proton acceptor
V. Important - Proton is the same as a (Hydrogen ion H+)

15. Identify the Bronsted acids/ bases in each case
An acid is a proton donor
A base is a proton acceptor

16. A conjugate acid – base pair
Reversible reactions
Some reactions can go in both directions, forward and backward
NH4+ H NH3 +H30+
Conjugate base
Bronsted acid
Bronsted base
Conjugate acid
Conjugate means having something in common but also opposites in some ways
A conjugate acid – base pair
an acid and a base by differ in structure by a proton

17. Self ionisation of water
Water can dissociate itself the following way:
H H+ + OH-
In a sample of water at room temperature this will only happen to a very small number of molecules

18. The ionic product of water
Kw = [OH-][H+]
(Note - Square Brackets mean concentration in moles per litre)
At 25OC Kw = 1 x 10-14
As temperature increases Kw will increase as more water molecules ionise.
Can you guess why reaction rates increase with increasing temperature?

19. Regardless of how many there are!!
H H+ + OH-
So in water,
[H+] = [OH-]
Regardless of how many there are!!

20. Remember that Kw = [OH-][H+] 1 x 10-14 = [OH-] [H+] at 25OC
We can also say
Kw = [H+][H+] Or
Kw = [H+]2
From this
1 x =[H+]2
√ 1 x = [H+]
1 x 10-7 = [H+] at 25OC
Also 1 x 10-7 = [OH-] at 25OC
Once number of h+ and oh are the same the solution is balanced and is nuetral.
Idea with the pH scale. Balanced is nuetral.

21. In any solution If [H+] = [OH-] The solution is neutral
If [H+] > [OH-] The solution is acidic
If [H+] < [OH-] The solution is basic

22. pH

23. the square brackets mean concentration in moles per litrepH
Sorensen – a Danish chemist
Expressed the acidity of a solution by measuring the amount of H+ ions present in a solution and using the formula:
To find out what Log base 5 (25) is, we'd ask ourselves "what power do you raise 5 to to get 25?" Since 5^2 = 25, the answer to this one is 2. So the Logarithm to the base 5 of 25 is 2.
pH= - log10 [H+],
the square brackets mean concentration in moles per litre

24. Example 1:
A solution has a concentration of 10-4 moles of H+ per litre.
What is the pH?
pH= - log10 [H+],
pH= - log10 [10-4],
pH= 4

25. Example 2:
A solution has a concentration of 7x10-7 moles of H+ per litre.
What is the pH?
pH= - log10 [H+],
pH= - log10 [7 x10-7],
pH= 6.15

26. [H+] = 1.995 X 10-4 moles per litre
Example 3:
A solution has a pH of 3.7.
What is the concentration of hydrogen ions in moles per litre?
pH= - log10 [H+],
3.7 = - log10 [H+],
Antilog
INV AND THEN LOG
OG 10 to the x
[H+] = antilog - 3.7
[H+] = X 10-4 moles per litre

27. The PH scale The pH of an acidic solution is less than 7.
The pH scale is a scale from 0 – 14 which tells how acidic or basic a solution is.
The pH of an acidic solution is less than 7.
The pH of an neutral solution is 7.
The pH of an basic solution is more than 7.

28. Measuring the pH of a solution:
Universal indicator
Dip the universal indicator paper into the solution.
Compare the colour of the paper to the scale supplied with the indicator to find the pH.

29. Measuring the pH of a solution:
pH meter
Dip the pH meter into the solution.
Read the pH off the meter

31. pH scale

32. Limitations of the pH scale
You can only find the pH of a substance if it is in a dilute aqueous solution.
It only really works at 25oC

33. Strong acids
Strong acids fully dissociate in water to produce H+ ions.
So for a strong acid, like HCl, in water the following happens:
HCl H+ + Cl-

34. Calculating the pH of a strong acid
Example:
Calculate the pH of a 0.01 M HCl solution:
HCl H+ + Cl-
0.01 M M
pH= - log10 [H+],
pH= - log10 [0.01],
pH= 2

35. HNO3 H+ + NO3 0.03 M 0.03 M pH= - log10 [H+], pH= - log10 [0.03], pH=
Example:
Calculate the pH of a 0.03 M HNO3 solution:
HNO3 H+ + NO3
0.03 M M
pH= - log10 [H+],
pH= - log10 [0.03],
pH=

36. Example:
Calculate the pH of a 0.5 M HF solution:
HF H+ + F-
0.5 M M
pH= - log10 [H+],
pH= - log10 [0.5],
pH=

37. Example 3 The concentration of a solution of HCl is 7.3g per litre.
(i) What is the concentration of the solution in moles per litre?
7.3g of HCl in one litre of solution.
Number of moles of HCl = 7.3
36.5(mass of one mole)
Number of moles of HCl in one litre = 0.2

38. Example 3 HCl H+ + Cl- 0.2 M 0.2 M pH= - log10 [H+],
(ii) What is the pH of the solution?
Number of moles of HCl = 0.2
HCl H+ + Cl-
0.2 M M
pH= - log10 [H+],
pH= - log10 [0.2],
pH= 0.69

39. Example 4 The concentration of a solution of HNO3 is 6.3g per litre.
(i) What is the pH?
6.3g of HNO3 in one litre of solution.
Number of moles of HNO3 = 6.3
63(mass of one mole)
Number of moles of HNO3 in one litre = 0.1

40. Example 4 HNO3 H+ + NO3- 0.1 M 0.1 M pH= - log10 [H+],
(ii) What is the pH of the solution?
Number of moles of HCl = 0.1
HNO3 H+ + NO3-
0.1 M M
pH= - log10 [H+],
pH= - log10 [0.1],
pH= 1

41. Find the pH of a 0.4M solution of sulphuric acid.
An unusual case
H2SO4 2H+ + SO4-2
Find the pH of a 0.4M solution of sulphuric acid.

42. Strong bases NaOH Na+ + OH-
Strong bases fully dissociate in water to produce OH- ions.
So for a strong base, like NaOH, in water the following happens:
NaOH Na+ + OH-

43. To find the pH of a strong base
There are two steps
1. Use this formula
pOH= - log10 [OH-]
2. pH = 14 - pOH

44. To find the pH of a strong base
Example 1:
Calculate the pH of a 0.5 M NaOH solution:
To find the pH of a strong base
Two steps
1. Use this formula:
pOH= - log10 [OH-]
pOH= - log10 [0.5]
pOH=
2. pH = 14 – pOH
pH = 14 –
pH =

45. To find the pH of a strong base
Example 2:
Calculate the pH of a 0.2 M KOH solution:
To find the pH of a strong base
Two steps
1. Use this formula:
pOH= - log10 [OH-]
pOH= - log10 [0.2]
pOH=
2. pH = 14 – pOH
pH = 14 –
pH =

46. Example 3 The concentration of a solution of KOH is 5.6g per litre.
(i) What is the concentration of the solution in moles per litre?
5.6g of KOH in one litre of solution.
Number of moles of KOH = 5.6
56(mass of one mole)
Number of moles of KOH in one litre = 0.1

47. Example (ii) What is the pH of the solution?
Number of moles of KOH= 0.1
Two steps
pOH= - log10 [OH-]
pOH= - log10 [0.1]
pOH=
2. pH = 14 – pOH
pH = 14 –
pH =

48. Example 4 The concentration of a solution of NaOH is 8g per litre.
(i) What is the concentration of the solution in moles per litre?
8g of NaOH in one litre of solution.
Number of moles of NaOH = 8
40(mass of one mole)
Number of moles of NaOH in one litre = 0.2

49. Example (ii) What is the pH of the solution?
Number of moles of KOH= 0.1
Two steps
pOH= - log10 [OH-]
pOH= - log10 [0.1]
pOH=
2. pH = 14 – pOH
pH = 14 –
pH =

50. Example 4 The concentration of a solution of NaOH is 8g per litre.
(i) What is the concentration of the solution in moles per litre?
8g of NaOH in one litre of solution.
Number of moles of NaOH = 8
40(mass of one mole)
Number of moles of NaOH in one litre = 0.2

51. Example (ii) What is the pH of the solution?
Number of moles of NaOH= 0.2
Two steps
pOH= - log10 [OH-]
pOH= - log10 [0.2]
pOH=
2. pH = 14 – pOH
pH = 14 –
pH =

52. Calculating pHs of weak acids and bases

53. Weak acids
A weak acid only slightly dissociates in water to produce H+ ions.
HA H+ + A-
Ka is the acid dissociation constant. It will tell you to what extent a weak acid will actually dissociate in water.

54. Useful formulas for doing calculations on weak acids
pH= - log10 [H+]
[H+] = √Ka x [Acid]
****Square brackets mean concentration in moles per litre!

55. But [H+] is not given for a weak acid [H+] = √Ka x [Acid]
Calculate the pH of a 0.1 solution of methanoic acid given that the value of the acid dissociation constant is 1.8 X 10-4
pH= - log10 [H+]
But [H+] is not given for a weak acid
[H+] = √Ka x [Acid]
[H+] = √1.8 x 10-4 x [0.1]
[H+] = √.00018
[H+] =
pH= - log10 [0.0042] = 2.37

56. Weak bases
A weak base only slightly dissociates in water to produce OH- ions.
NH3 +H20 NH4+ + OH-
KB is the BASE dissociation constant. It will tell you to what extent a weak base will actually cause the production of OH- in water.

57. Useful formulas for doing calculations on weak bases
pH = 14 - pOH
pOH= - log10 [OH-]
[OH-] = √Kb x [Base]
****Square brackets mean concentration in moles per litre!

58. Calculate the pH of a 0.01 solution of ammonia given that the value of the base dissociation constant is 1.8 X 10-5
pH = 14 - pOH
pOH= - log10 [OH-]
But [OH-] is not given for a weak base
[OH-] = √Kb x [Base]
[OH-] = √1.8 x 10-5 x [0.01]
[OH- ] = √
[OH- ] =
pOH= - log10 [ ] = 3.37
pH = 14 – pOH
Ph = 14 – 3.37 = 10.6

59. Acid – Base Indicators

60. Acid-base indicators
Indicators are substances that change colour depending on the pH of the solution in which they are placed

61. Lab indicators

62. How indicators work
They are weak acids mostly so will act as follows..
HIn H+ + In-
They have a different colour depending on which form they are in – dissociated or undissociated

63. Causing a colour change to blue
Example : Litmus
HIn H+ + In-
BLUE
RED
What happens when a base is added to red Litmus indicator?
The base will accept H+ ions from the reaction and make it go to the left hand side,
Causing a colour change to blue
What happens when an acid is added to blue Litmus indicator?
The acid will donate H+ ions and these will react with the indicator, making it go red.

64. Methyl orange At pH 4 and 5 methyl orange looks an indistinct colour1 2 3 4 5 6 7 8 9 10 11
Methyl orange P Y
At pH 4 and 5 methyl orange looks an indistinct colour

65. Litmus At pH 5,6,7 litmus looks an indistinct colour PH 1 2 3 4 5 6 78 9 10 11
Litmus R B
At pH 5,6,7 litmus looks an indistinct colour

66. Phenolphthalein At pH 8,9 phenolphtalein has an indistinct colour PH 12 3 4 5 6 7 8 9 10 11
Phenolphthalein C B
At pH 8,9 phenolphtalein has an indistinct colour

67. Titration curves
Measuring the pH changes in a reaction between an acid and a base
Often the pH will change quite suddenly, and an indicator can be used to detect this end point

68. Picking the correct indicator
Titrating a strong acid against a strong base
At the end point the pH jumps from 3 to 10 suddenly.
Which indicator would tell when this endpoint has been reached?
IT MUST SHOW A CLEAR COLOUR CHANGE FROM 3 – 10!! PH 1 2 3 4 5 6 7 8 9 10 11
Phenolphthalein C B PH 1 2 3 4 5 6 7 8 9 10 11
Litmus R B PH 1 2 3 4 5 6 7 8 9 10 11
Methyl orange P Y

69. Picking the correct indicator
Titrating a strong acid against a weak base
At the end point the pH jumps from 3 to 7 suddenly.
Which indicator would tell when this endpoint has been reached?
IT MUST SHOW A CLEAR COLOUR CHANGE FROM 3 – 7!! PH 1 2 3 4 5 6 7 8 9 10 11
Phenolphthalein C B PH 1 2 3 4 5 6 7 8 9 10 11
Litmus R B PH 1 2 3 4 5 6 7 8 9 10 11
Methyl orange P Y

70. Picking the correct indicator
Titrating a weak acid against a strong base
At the end point the pH jumps from 7 to 10 suddenly.
Which indicator would tell when this endpoint has been reached?
IT MUST SHOW A CLEAR COLOUR CHANGE FROM 7 – 10!! PH 1 2 3 4 5 6 7 8 9 10 11
Phenolphthalein C B PH 1 2 3 4 5 6 7 8 9 10 11
Litmus R B PH 1 2 3 4 5 6 7 8 9 10 11
Methyl orange P Y

71. Picking the correct indicator
Titrating a weak acid against a weak base
There is no sharp change in pH at the end point.
It is difficult to find the exact point of neutralisation relying on indicator colour.
A pH meter could be used PH 1 2 3 4 5 6 7 8 9 10 11
Phenolphthalein C B PH 1 2 3 4 5 6 7 8 9 10 11
Litmus R B PH 1 2 3 4 5 6 7 8 9 10 11
Methyl orange P Y