1. Starter - Calculating moles
g of H2O g of CO g of NH g of C2H5OH g of C2H g of SO g of SO g of HBr g of H2SO g of HNO3

2. 4.9 describe experiments to carry out acid-alkali titrations.

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. Using a Volumetric Pipette
Using a pipette measure out 25cm3 of water and transfer it into a graduated cylinder

7. Using a burette
Using a burette measure out 25cm3 of water and transfer it into a graduated cylinder

8. Calculations in a titration
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)

9. Did you get?
2 Moles

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

11. 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

12. A triangle to learn
What are the units for each of the following?

13. 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.

14. 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

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

16. 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

17. Plenary
Next lesson you will be carrying out a titration between hydrochloric acid and an unknown solution of sodium hydroxide
On seesaw upload your plan for what you will be doing
Must include
Equipment needed
Method
Measurements you will take
How you will calculate the concentration of sodium hydoxide