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strong acid strong base

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1 strong acid strong base
pH CURVES & INDICATORS How pH indicators work methyl orange phenolphthalein Choosing an appropriate indicator pH curves strong acid strong base strong acid weak base weak acid strong base weak acid weak base SUMMARY diprotic acid H2C2O4 / NaOH diprotic base Na2CO3 / HCl

2 INDICATORS HIn  H+ + In- colour 1 colour 2
Indicators are weak acids which have a different colour to their conjugate base HIn  H+ + In- colour colour 2 low pH: equilibrium pushed left = colour 1 high pH: equilibrium pushed right = colour 2

3 Methyl orange pH < 3.2 pH > 4.4

4 acid end-point alkali

5 Phenolphthalein pH < 8.2 pH > 10.0

6 phenolphthalein acid alkali

7 INDICATORS For an indicator to work in a titration:
The pH range of the indicator’s colour change must be within the range of the pH change at the end-point.

8 INDICATORS Indicator colour at low pH pH range of colour change
high pH methyl orange red 3.2 – 4.4 orange phenolphthalein colourless 8.2 – 10.0 purple

9 Strong acid – Strong base
pH at equivalence = 7

10 Strong acid – Strong base

11 Strong acid – Strong base

12 Strong acid – Weak base pH at equivalence < 7

13 Strong acid – Weak base

14 Strong acid – Weak base

15 Weak acid – Strong base pH at equivalence > 7

16 Weak acid – Strong base

17 Weak acid – Strong base

18 depends on relative strength of acid and base
Weak acid – Weak base pH at equivalence depends on relative strength of acid and base

19 Weak acid – Weak base

20 Weak acid – Weak base

21 SUMMARY

22 SUMMARY

23 SUMMARY

24 H2C2O4 v NaOH H2C2O4 + OH- HC2O4- + H2O HC2O4- + OH- C2O42- + H2O

25 H2C2O4 v NaOH H2C2O4 + OH- HC2O4- + H2O HC2O4- + OH- C2O42- + H2O

26 H2C2O4 v NaOH H2C2O4 + OH- HC2O4- + H2O HC2O4- + OH- C2O42- + H2O

27 Na2CO3 v HCl CO32- + H+ HCO3- HCO3- + H+ H2O + CO2

28 Na2CO3 v HCl CO32- + H+ HCO3- HCO3- + H+ H2O + CO2

29 Na2CO3 v HCl CO32- + H+ HCO3- HCO3- + H+ H2O + CO2


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