Starter - Calculating moles 1. 9.00 g of H2O 2. 88.0 g of CO2 3. 1.70 g of NH3 4. 230 g of C2H5OH 5. 560 g of C2H4 6. 0.640 g of SO2 7. 80.0 g of SO3 8. 18.0 g of HBr 9. 0.0960 g of H2SO4 10. 3.15 g of HNO3

4.9 describe experiments to carry out acid-alkali titrations.

Determining the pH and concentration of an acid or alkali

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?

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

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

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

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)

Did you get? 2 Moles

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

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

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

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.

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

Can you fill in your little grid from this information?

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

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