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Chem paper 3 revison

QuestionAnswer
Suggest how antibumping granules prevent bumping during reflux? Prevent large bubbles forming
Why is an excess of Sodium hydroxide used? Ensure all of ester reacts.
Suggest why an electric heater is used rather than a Bunsen burner in this hydrolysis? The ethanol is flammable
State why reflux is used in this hydrolysis? Reflux allows reactant vapours (of volatile organic compounds) to be returned to the reaction mixture / does not allow any reactant vapour to escape
Write an equation for the reaction between sodium benzoate and hydrochloric acid. C6H5COONa + HCl --> C6H5COOH + NaCl
Suggest why sodium benzoate is soluble in cold water but benzoic acid is insoluble in cold water. [ Sodium benzoate soluble because it is ionic Benzoic acid insoluble because: despite the polarity of the COOH group / ability of COOH to form H-bonds, the benzene ring is non-polar
After the solid benzoic acid has been filtered off, it can be purified. Describe the method that the student should use to purify the benzoic acid. Dissolve crude product in hot solvent/water of minimum volume Filter (hot to remove insoluble impurities) Cool to recrystallise Filter under reduced pressure / with Buchner/Hirsch apparatus wash (with cold solvent) and dry
Why is percentage yield greater than 100? Product not dried properly or impurities are present
What happens when a mixture is refluxed? A mixture of liquids heated to boiling point for a prolonged time Vapour is formed which escapes from the liquid mixture, is changed back into liquid and returned to the liquid mixture Any ethanal and ethanol that initially evaporates can be oxidised
Write a half-equation for the overall oxidation of ethanol into ethanoic acid CH3CH2OH + H2O CH3COOH + 4H+ + 4e–
Created by: ksatti12
 

 



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