1. Titration calculations

2. Learning intentions You will be able to
remember the steps involved in doing a titration
identify the useful facts in the questions
be able to calculate an unknown concentration

3. Determining the pH and concentration of an acid or alkali

4. Describe in your own words how you could use this apparatus to determine the concentration of an unknown acid or alkali.
Could you label the diagram?

5. Model Answer
Measure unknown concentration solution into conical flask with pipette
Pour known solution into burette
Note initial reading
Use an indicator such as phenolphthalein to tell end point
Note final reading or amount used

6. Exam question

7. Calculations Reminder – turning mass into moles DIVIDE BY THE Mr
Test yourself:
How many moles are in 73g hydrochloric acid?
(Relative atomic masses: H 1; Cl 35.5)

8. Did you get?
2 Moles

9. Concentration
Concentration is measured in mols per litre or moldm-3
What is the concentration in moles of 73gdm-3
2 moldm-3

10. gdm-3 converting moldm-3
For sulfuric acid, H2SO4, convert 49gdm-3 into molsdm-3
(Relative atomic masses: H 1; S 32; O 16)
Did you get:
0.5 moldm-3

11. An equation to learn
Concentration = Moles / Volume Can you rearrange for moles? Can you rearrange for volume?

12. Calculating unknown concentration
1) Find the moles that have reacted (of the known substance) Use: concentration x Volume = Moles 2) Find the mole that have reacted (of the unknown substance) Use a ratio Moles acid = Moles alkali . number of ‘OH’ ions in alkali number of H ions in acid 3) Calculate concentration Use concentration = moles/volume Getting information out of a question… Draw yourself a little grid.

13. Calculating unknown concentration
Getting information out of a question… Draw yourself a little grid.
Concentration (molsdm-3)
Volume (dm-3)
Moles
Number of H/OH ions
Acid
Alkali

14. Can you fill in your little grid from this information?

15. Calculating unknown concentration
Getting information out of a question… Draw yourself a little grid.
Concentration (molsdm-3)
Volume (dm-3)
Moles
Number of H/OH ions
Acid ?
35/1000
=0.035 1
Alkali
0.40
25/1000
=0.025

16. Learning intentions You will be able to
remember the steps involved in doing a titration
identify the useful facts in the questions
be able to calculate an unknown concentration