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Assessed Practical Preparation

Assessed Practical Preparation. Quantitative Skills. What is it worth?. Qualitative. Colour Change Production of Gases Suggesting Chemical equations for observations. Quantitative. Calculations Titrations, Water of Crystallisation, Enthalpy. Evaluative. % error

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Assessed Practical Preparation

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  1. Assessed Practical Preparation Quantitative Skills

  2. What is it worth?

  3. Qualitative • Colour Change • Production of Gases • Suggesting Chemical equations for observations Quantitative • Calculations • Titrations, Water of Crystallisation, Enthalpy Evaluative • % error • Calculations based on given results • Graph drawing • Suggesting improvements on a given method • Suggesting alternative ways of doing things

  4. Calculations • Titrations, Water of Crystallisation, Enthalpy Key equations to learn:

  5. Recording your Results Take care with recording results ( marks may be available): Mr P’s top tips: Don't get confused between Final and Initial Readings If you are starting on zero you must record this as 0.00 not 0 or 0.0 All titrations should be recorded to the nearest 0.05cm3 If the table asks for the mean titre to be recorded to 1 decimal place- do it! The accurate titres should be within 0.1cm3 of each other for max accuracy Use you 2 closes titres to calculate the mean NOT all of them.

  6. 21.15 cm3 The meniscus lays between the two lines

  7. Carrying Out a titration 3 Marks could be available for accuracy...so Y12 make notes on the following techniques • Cleaning Glass ware http://www.youtube.com/watch?v=AU6ozDDlMTE • Preparing the Burette http://www.youtube.com/watch?v=MuKh3s73IAM&feature=relmfu • Preparing the pipette http://www.youtube.com/watch?v=DKRQ95QfWNY&feature=relmfu • Performing the titration http://www.youtube.com/watch?v=iiedQ6dWZiA&feature=relmfu

  8. How does titration work?

  9. 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...

  10. H2SO4 + 2KOH  K2SO4 + 2H2O What is the concentration of the sulphuric acid if 24.6cm3 of the acid was needed to neutralise 25cm3 of 0.1 moldm-3 KOH. Calculate Moles of KOH used Calculate moles of H2SO4 in titre Calculate moles of H2SO4 in 250cm3 standard solution. Calculate the Concentration of Sulphuric acid in moldm-3 What is the concentration in gdm-3?

  11. Final problem 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? 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

  12. 310310 tonnes

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