Assessed Practical Preparation

Quantitative Skills

What is it worth?

Assessed Practical

Quantitative

QualitativeEvaluative

Qualitative

•Colour Change•Production of Gases•Suggesting Chemical equations for observations Quantitative

•Calculations•Titrations, Water of Crystallisation, EnthalpyEvaluative

•% error•Calculations based on given results•Graph drawing•Suggesting improvements on a given method•Suggesting alternative ways of doing things

•Calculations•Titrations, Water of Crystallisation, Enthalpy

Key equations to learn:

Recording your Results

Take care with recording results ( marks may be available):

Mr P’s top tips:1. Don't get confused between Final and Initial Readings2. If you are starting on zero you must record this as 0.00 not 0 or 0.03. All titrations should be recorded to the nearest 0.05cm3

4. If the table asks for the mean titre to be recorded to 1 decimal place- do it!5. The accurate titres should be within 0.1cm3 of each other for max accuracy6. Use you 2 closes titres to calculate the mean NOT all of them.

21.15 cm3

The meniscus lays between the two lines

Carrying Out a titration

• Cleaning Glass ware http://www.youtube.com/watch?v=AU6ozDDlMTE

• Preparing the Burettehttp://www.youtube.com/watch?v=MuKh3s73IAM&feature=relmfu • Preparing the pipettehttp://

www.youtube.com/watch?v=DKRQ95QfWNY&feature=relmfu • Performing the titrationhttp://www.youtube.com/watch?v=iiedQ6dWZiA&feature=relmfu

3 Marks could be available for accuracy...so Y12 make notes on the following techniques

9 of 31 © Boardworks Ltd 2009

How does titration work?

Calculations

• Ensure you bring a calculator• We have looked a number of titration

calculations in class.• Examples in textbook p28-29• Try the example on the following slides...

H2SO4 + 2KOH K2SO4 + 2H2OWhat is the concentration of the sulphuric acid if 24.6cm3 of the acid was needed to neutralise 25cm3 of 0.1 moldm-3 KOH.

1. Calculate Moles of KOH used2. Calculate moles of H2SO4 in titre3. Calculate moles of H2SO4 in 250cm3 standard solution.

4. Calculate the Concentration of Sulphuric acid in moldm-3

5. What is the concentration in gdm-3?

All the fish in Mr O’Sullivan’s pond have died. On investigation the water was too acidic. He goes down to Swallows Aquatics to buy some Calcium Carbonate to neutralise the acid to a safe level. How much does he need in tonnes?

Final problem

Info:Equation: H2SO4 + CaCO3 CaSO4 + H2O + CO2

Approx volume of Pond= 1x 1014 dm3( he has a massive garden!)Concentration of the acid = 3.1 x 10-5 moldm-3

1 tonne = 1x106 g

• 310310 tonnes