Carboxylic acids questions
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This method is used to prepare a sample of ester F. Step 1 Mix 10 cm3 of propan-2-ol with 10 cm3 of ethanoic acid. Add 5 drops of concentrated sulfuric acid. Reflux this reaction mixture for 20 minutes. Step 2 Transfer the cooled reaction mixture to a separating funnel. Add 20 cm3 of aqueous sodium carbonate and shake the mixture. Step 3 Transfer the organic layer to a beaker and add 5 g of anhydrous magnesium sulfate. Decant off the organic liquid. Step 4 Collect the ester using simple distillation. (b) Describe how Step 1 should be done. In your description you should * give details of suitable equipment used to add each reagent to the reflux apparatus * draw a labelled diagram of the apparatus used for refluxing the reaction mixture * explain any safety precautions needed other than eye protection.
Stage 1 1a Measuring cylinder(s) for the propan-2-ol and ethanoic acid (size not required but if specified should be between 10 - 100 cm3) Allow 10cm3 / graduated pipette or burette 1b (Dropping/teat) pipette for sulfuric acid (NOT graduated or other qualification for pipette) Stage 2 Diagram e.g. below to include 2a Labelled condenser shown vertical and open at top and bottom i.e. in cross section 2b Labelled water in at the bottom and water out at the top of the vertical condenser 2c Labelled reaction flask recognisable as either pear shaped or round bottomed Stage 3 Safety Needs precaution AND reason for each suggestion 3a Use a fume cupboard/fume hood/well-ventilated lab space AND to avoid breathing in harmful/toxic/corrosive compounds 3b Wear gloves AND as compounds are corrosive 3c Add glass beads/chips (to the mixture before heating)/labelled as anti-bumping granules/chips AND to ensure smooth boiling/reduce size of bubbles 3d Use an electric heater/water bath AND as compounds are flammable
In Step 2 the reaction mixture from Step 1 is shaken with aqueous sodium carbonate. State the purpose of the sodium carbonate. Suggest a precaution that should be taken while this mixture is shaken in the separating funnel. Give a reason for your suggested precaution.
M1 To neutralise/remove/react with (excess) acid M2 Remove stopper/bung OR tip the funnel upside down and open the tap M3 There will be a build up of pressure/gas/carbon dioxide M3 must be linked to their precaution in M2 OR M2 Allow add stopper M3 To prevent spillage
Give the reason for the use of anhydrous magnesium sulfate in Step 3.
Drying agent/To remove water
State why ethanoic anhydride is preferred to ethanoyl chloride for this preparation.
Ethanoic anhydride/It is less/not corrosive OR Ethanoic anhydride/It does not form strong acid/HCl /(only) forms weak/ethanoic/carboxylic acid OR Ethanoic anhydride/It is less/not vulnerable to hydrolysis
Suggest how the purity of the ester can be confirmed during the distillation in Step 4.
Compare boiling point to a data book/known value
Suggest the role of the concentrated phosphoric acid.
Catalyst
Suggest why reflux is not essential when the flask is heated to 85 °C for 10 minutes.
Boiling points are above 85 °C
Suggest the identity of two impurities present in the filtered solid aspirin before it is washed in Step 6 of the method
Any 2 of: * Ethanoic acid * Phosphoric acid * 2-hydroxybenzenecarboxylic acid * Ethanoic anhydride * Water
https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FChemistry%2FA-level%2FTopic-Qs%2FAQA%2FOrganic-II%2F3.09-Carboxylic-Acids-and-Derivatives%2FSet-J%2FCarboxylic%20Acids%20and%20Derivatives%20MS.pdf Complete and label the diagram below to show how the impure solid is filtered. 2 F
Describe the recrystallisation process used to purify the aspirin. Include the method and apparatus used.
M1 Dissolve crude product in hot solvent (water and ethanol) Ignore initial filtration M1 not wrong solvent if named M2 of minimum volume M2 Allow reference to saturated solution as alternative to minimum volume M3 Filter (hot to remove insoluble impurities) M3 Ignore method of filtration Allow decant M4 Cool (to recrystallise) M5 Filter under reduced pressure / with Buchner/Hirsch apparatus M6 Wash (with cold solvent) and dry
State the physical property that is measured to check the purity of the aspirin. Describe two ways the result would show that the product is impure.
M1 Melting point M1 Ignore boiling point M2 Lower (than data book value) M2/3 In either order M2 Ignore ‘different’ M2 ECF for ‘higher’ if b.pt in M1 M2If b.pt in M1 NOT ‘lower’ M3 Melts over a (wide) range of temperature (rather than sharp/narrow range if pure)
Palmitic acid burns in air. In a calorimetry experiment, combustion of 387 mg of palmitic acid increases the temperature of 0.150 kg of water from 23.9 °C to 37.5 °C Calculate a value, in kJ mol–1, for the enthalpy of combustion of palmitic acid in this experiment. Give your answer to the appropriate number of significant figures. The specific heat capacity of water is 4.18 J K–1 g–1 Mr of palmitic acid si liek 256
M1 M r = 256 M2 n(CH3(CH2)14COOH) = = 1.51 × 10-3 M3 Q = 150 × 4.18 × 13.6 = 8527.2 (J) M4 ∆H = ÷ 1000 = (-)5641 M5 ∆H = -5640 kJ mol-1 Must be negative and 3sf (allow ecf on M4)
State how the value calculated in part (b) is likely to differ from data book values. Give one reason, other than heat loss, for this difference
Less exothermic Incomplete combsution
The reaction mixture is flammable. Suggest how the reaction mixture should be heated in step 1.
ELectric heater
Role of H2SO4
Catalyusts
State why sodium carbonate is added to the distillate in step 4. Explain why there is a build-up of pressure in the separating funnel.
M1 to neutralise/react with/remove the acid ALLOW carboxylic/ethanoic and/or sulfuric IGNORE react with/neutralise the distillate/mixture IGNORE to act as a base NOT if incorrect acid named M2 carbon dioxide / gas is produced
Give a reason why two layers form in the separating funnel. Suggest why ethyl ethanoate forms the upper layer.
M1 ethyl ethanoate/it is immiscible with / insoluble in water ALLOW water/solution and ethyl ethanoate/it do not mix, OR aqueous and organic layers do not mix ALLOW ethyl ethanoate/it is hydrophobic IGNORE references to polarity / intermolecular forces M2 ethyl ethanoate/it is less dense / has lower density (than water)
State why anhydrous calcium chloride is added in step 6.
to remove/absorb water / as a drying agent
Suggest a reason why the percentage yield is not 100%
reaction is an equilibrium/reversible
b) Name the type of reaction shown in the diagram above. https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FChemistry%2FA-level%2FTopic-Qs%2FAQA%2FOrganic-II%2F3.09-Carboxylic-Acids-and-Derivatives%2FSet-J%2FCarboxylic%20Acids%20and%20Derivatives%20QP.pdf
(b) (Alkaline/base) hydrolysis 1
(c) Deduce the role of the CH3O− ion in step 3 shown in the diagram above. https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FChemistry%2FA-level%2FTopic-Qs%2FAQA%2FOrganic-II%2F3.09-Carboxylic-Acids-and-Derivatives%2FSet-J%2FCarboxylic%20Acids%20and%20Derivatives%20QP.pdf
(c) Base
A triester in vegetable oil reacts with sodium hydroxide in a similar way. Give a use for a product of this reaction
Soap