AQA A Level Chemistry - Paper 3
Experiments
(some are partly done) qualitative tests for ions and organic functional groups, a b c f h, k, volatges. -
correct answer
Acid-Base Titration - correct answerrinse equipment (burette with acid, pipette with alkali, conical flask
with distilled water)
•pipette 25 cm3 of alkali into conical flask
•touch surface of alkali with pipette ( to ensure correct amount is added)
•adds acid solution from burette
•make sure the jet space in the burette is filled with acid
•add a few drops of indicator and refer to colour change at end point
•phenolphthalein [pink (alkali) to colourless (acid): end point pink colour just disappears] [use if NaOH is
used] •methyl orange [yellow (alkali) to red (acid): end point orange] [use if HCl is used]
•use a white tile underneath the flask to help observe the colour change
•add acid to alkali whilst swirling the mixture and add acid drop wise at end point
•note burette reading before and after addition of acid •repeats titration until at least 2 concordant
results are obtained- two readings within 0.1 of each other
Anti-Bumping Granules - correct answerSmall, rough pieces of silica that are added to the mixture
before reflux. They provide a rough surface on which small gas bubbles can grow, avoiding bumping.
They promote smooth, even boiling. ??FINISHED HERE
Checking Purity Of An Organic Solid - correct answer1. Place some solid in a melting point tube sealed at
one end
2. Place in m.p. apparatus and heat slowly near the melting point
3. Record the melting temperature and the temperature when it stops melting
4. Repeat and average the remperatures
5. Compare m.p. to data book values
, M.p. range of + or - 2°C = pure
Distillation - correct answerNB, oxidation: Dilute acid and less K2Cr2O7 than needed.
1. Heat liquid to boil and vaporise the most volatile component in the mixture. Anti-bumping granules
are used.
2. The vapour passes up from the flask and down into the condenser, where it is cooled by cold water
and ice, and condenses back to a liquid (the distillate) which is collected in the flask.
3. Any dissolved solids are left in solution because they have too high a boiling point to be distilled over .
Drying an Organic Liquid - correct answer1. Add a spatula of drying liquid (e.g. anhydrous CaCl2 or
MgSO4) to the organic liquid
2. Swirl
3. Add more of the drying agent until the liquid changes from cloudy to clear
4. Filter or decant off the liquid into a clean, dry flask
Extrapolation (Enthalpy Changes) - correct answer1. Measure 50g of water into polystyrene cup held in a
beaker
2. Start stop clock and record temp of water every minute for 3 minutes
3. On minute 4, add the 5g solid and stir vigorously
4. Read temp of solution every min for 15 mins
5. Plot graph of temp vs time
6. Extrapolate temp readings back from min 15 to min 4
7. Draw best fit line to give mean start temp from min 1 to min 3
8. Calculate temperature change at minute 4
How pH Changes When A Weak Acid Reacts With A Strong Base - correct answer1. Rinse pH probe
thoroughly with deionised water and shake gently. Place it in the standard pH 7 buffer solution to
calibrate.
Experiments
(some are partly done) qualitative tests for ions and organic functional groups, a b c f h, k, volatges. -
correct answer
Acid-Base Titration - correct answerrinse equipment (burette with acid, pipette with alkali, conical flask
with distilled water)
•pipette 25 cm3 of alkali into conical flask
•touch surface of alkali with pipette ( to ensure correct amount is added)
•adds acid solution from burette
•make sure the jet space in the burette is filled with acid
•add a few drops of indicator and refer to colour change at end point
•phenolphthalein [pink (alkali) to colourless (acid): end point pink colour just disappears] [use if NaOH is
used] •methyl orange [yellow (alkali) to red (acid): end point orange] [use if HCl is used]
•use a white tile underneath the flask to help observe the colour change
•add acid to alkali whilst swirling the mixture and add acid drop wise at end point
•note burette reading before and after addition of acid •repeats titration until at least 2 concordant
results are obtained- two readings within 0.1 of each other
Anti-Bumping Granules - correct answerSmall, rough pieces of silica that are added to the mixture
before reflux. They provide a rough surface on which small gas bubbles can grow, avoiding bumping.
They promote smooth, even boiling. ??FINISHED HERE
Checking Purity Of An Organic Solid - correct answer1. Place some solid in a melting point tube sealed at
one end
2. Place in m.p. apparatus and heat slowly near the melting point
3. Record the melting temperature and the temperature when it stops melting
4. Repeat and average the remperatures
5. Compare m.p. to data book values
, M.p. range of + or - 2°C = pure
Distillation - correct answerNB, oxidation: Dilute acid and less K2Cr2O7 than needed.
1. Heat liquid to boil and vaporise the most volatile component in the mixture. Anti-bumping granules
are used.
2. The vapour passes up from the flask and down into the condenser, where it is cooled by cold water
and ice, and condenses back to a liquid (the distillate) which is collected in the flask.
3. Any dissolved solids are left in solution because they have too high a boiling point to be distilled over .
Drying an Organic Liquid - correct answer1. Add a spatula of drying liquid (e.g. anhydrous CaCl2 or
MgSO4) to the organic liquid
2. Swirl
3. Add more of the drying agent until the liquid changes from cloudy to clear
4. Filter or decant off the liquid into a clean, dry flask
Extrapolation (Enthalpy Changes) - correct answer1. Measure 50g of water into polystyrene cup held in a
beaker
2. Start stop clock and record temp of water every minute for 3 minutes
3. On minute 4, add the 5g solid and stir vigorously
4. Read temp of solution every min for 15 mins
5. Plot graph of temp vs time
6. Extrapolate temp readings back from min 15 to min 4
7. Draw best fit line to give mean start temp from min 1 to min 3
8. Calculate temperature change at minute 4
How pH Changes When A Weak Acid Reacts With A Strong Base - correct answer1. Rinse pH probe
thoroughly with deionised water and shake gently. Place it in the standard pH 7 buffer solution to
calibrate.
