1. Acid Dissociation…
Work together in groups. How many definitions do you know for acids?

2. Acid Dissociation…
The AS definition of an acid is:
“A molecule that dissociates to release a proton when dissolved in water”
It is a PROTON DONATOR

3. Acid Dissociation…
There are a number of compounds that you need to instantly recognise as acids:
HCl
H2SO4
HNO3
Anything ending -COOH

4. Alkali Dissociation…
The AS definition of an alkali is:
“A molecule that dissociates to release a hydroxide ion when dissolved in water”
It is a PROTON ACCEPTOR

5. Alkali Dissociation…
There are a number of compounds that you need to instantly recognise as alkalis:
NH3
Metal oxides - MO
Metal hydroxides - MOH
Amines - NH2

6. Dissociation of water…
This is one of the few times where we treat water as an ionic compound.
H2O OH H+
In the presence of an acid:
H2O + H+ H3O+

7. Dissociation of water…
Water behaves as both an acid and an alkali, depending on the pH of a compound added to it.
It is described as being AMPHOTERIC.
Amino acids are also amphoteric as they contain both
NH2
COOH

8. Strong vs Concentrated…
Terminology is likely to get you in trouble in A level chemistry.
Up until now strong and concentrated have been interchangeable. As have weak and dilute.
In your groups define all 4 terms.

9. Strong vs Concentrated…
“A high number of particles in a given volume of a fluid”
Dilute
“A low number of particles in a given volume of a fluid”

10. Strong vs Concentrated…
“A compound that FULLY DISSOCIATES into its metal and non-metal parts”
Weak
“A compound that PARTIALLY DISSOCIATES into its metal and non-metal parts”

11. Strong vs Concentrated…
Full dissociation means that ALL the particles dissociate as shown by:
HA  H+ + A-
Partially dissociation means that only some of the particles dissociate as shown by:
HA H+ + A-

12. We need balanced equations!
Titrations…
Titrations are used to find the concentration of an unknown solution by reacting with a solution of known concentration.
It uses the ratio of H+ in an acid to the non-metal component of an alkali.
More simply put:
We need balanced equations!

13. Titrations… The common indicators are: Methyl Orange Phenolphthalein
In order to perform a titration we need to be able to identify the point of neutralisation. To do this we use INDICATORS.
The common indicators are:
Methyl Orange
Phenolphthalein

14. The point of neutralisation is the FIRST PERMANENT COLOUR CHANGE
Titrations…
Methyl Orange:
Yellow in alkali
Red/Orange in acid
The point of neutralisation is the FIRST PERMANENT COLOUR CHANGE

15. The point of neutralisation is the FIRST PERMANENT COLOUR CHANGE
Titrations…
Phenolphthalein:
Pink in alkali
Colourless in acid
The point of neutralisation is the FIRST PERMANENT COLOUR CHANGE

16. Titrations…
Neither of these indicators change colour at pH7. So the choice of when we use it depends on where its “end point” pH lies

17. Strong acid/Strong alkali
Titrations…
Strong acid/Strong alkali
The end point for both indicators lie within the “equivalence point” of the reaction.
Both are therefore suitable.

18. Strong acid/Weak alkali
Titrations…
Strong acid/Weak alkali
The end point for only methyl orange lies within the “equivalence point” of the reaction.
Therefore only methyl orange is suitable.

19. Weak acid/Strong alkali
Titrations…
Weak acid/Strong alkali
Only the end point for phenolphthalein lies within the “equivalence point” of the reaction.
Therefore only phenolphthalein is suitable.

20. Titrations… Weak acid/Weak alkali
Neither indicator’s end point lies within the “equivalence point” of the reaction.
Therefore neither indicator is suitable.

21. Titrations…
13.5cm3 of 0.01M hydrochloric acid is required to neutralise 25cm3 of sodium carbonate. What is the concentration of the alkali?

22. Titrations… Write out the balanced equation
Calculate the moles of acid
Use the equation to calculate the moles of alkali
Calculate the concentration of the alkali
2HCl + Na2CO3 2NaCl + CO2 + H2O
n(HCl) = 0.01 * =1.35 * 10-4
n(Na2CO3) = (1.35 * 10-4)/2 =6.75 * 10-5
c(Na2CO3) = 6.75 * 10-5 / 0.025
= 2.7 * 10-3 M

23. Titrations…
In stretch and challenge question you will be expected to convert certain units. These are:
1ppm = 1mgdm-3
moldm-3 = gdm-3 / Mr