Practicals

Question 1

Molar volume of gas

Answer 1

-set up conical flask with bung and delivery tube attached to gas syringe
-place excess ethanoic acid in conical flask and add set mass of marble chips (CaCO3) and quickly place bung on
-measure volume of gas produced using gas syringe every 10secs until no more produced
-repeat 3x calculate mean and repeat for dif masses using same volume and concen of acid

Question 2

Preparing standard solution

Answer 2

-weigh out mass of required acid salt using weigh boat and weigh by difference and transfer to clean beaker and dissolve in distilled water using glass rod
-add solution to volumetric flask and add washings from weight boat and beaker to flask and rinse mouth
-fill with distilled water to 250cm3 mark
-add stopper and invert several times to mix

Question 3

Basic titration

Answer 3

-carry out trial titration to find approx end point and swirling over white tile
-carry out more accurate adding acid/base drop by drop when approaching end point and rinse sides
-repeat until concordant titres (0.1cm3) and calculate mean

Question 4

Rates of hydrolysis of halogenoalkanes

Answer 4

-three test tubes each with 1cm3 of ethanol and two drops of halogenoalkane and few drops of dilute nitric acid
-place test tubes in water bath along with test tube of silver nitrate and allow all to reach constant temp
-add 1cm3 silver nitrate to each test tube and start stopwatch
-measure time taken for precip to form

Question 5

Oxidation of ethanol

Answer 5

-place acidified K2Cr2O7 in pear shaped flask and add few anti-bumping granules (smoother boiling)
-add ethanol dropwise to pear shaped flask and stir to ensure complete mixing
-set of reflux/distillation apparatus and heating using Bunsen burner

Question 6

Chlorination of tertiary alcohol

Answer 6

-add conc HCl to alcohol in conical flask and swirl gently
-put rubber bung in and swirl flask gently, open bung and release pressure from time to time and repeat for 20mins
-add anhydrous calcium chloride, should be two layers
-transfer to separating funnel
-allow layers to separate and discard lower aq layer, keeping organic layer
-add sodium hydrogen carbonate solution to remove untreated HCl and swirl gently, stopper funnel and shake it and invert funnel and release pressure due to CO2 and repeat twice
-remove stopper and run off aq layer, run organic layer into conical flask and add anhydrous calcium chloride which acts as drying agent, swirl contents and allow to stand until clear and no longer clumping
-distil to purify

Question 7

How to test for bromide

Answer 7

Add chlorine water, produces orange solution if present

Question 8

How to test for OH groups (not phenols)

Answer 8

Add PCl5, misty fumes of HCl

Question 9

How to test for carboxylic acids

Answer 9

Add sodium carbonate, effervescence which will turn lime water cloudy

Question 10

How to test for metal cations

Answer 10

Add NaOH, dif precips of metal hydroxides produced

Question 11

Enthalpy change using Hess’s Law

Answer 11

-place one of reactants into polystyrene cup and place thermometer though cardboard lid into it
-start stopwatch and record temp of liquid every minute, at four mins add second reactant and at five mins continue taking temp readings for further ten mins
-plot temps on graph and extrapolate to find temp change
-repeat and calculate mean
-repeat for second reaction

Question 12

Iodine reactions (effect of iodine on rate of reaction)

Answer 12

-Mix aqueous propanone with sulfuric acid in a beaker.
2. Start the stop clock the moment you add iodine solution. Shake the beaker to mix well.
3. Using a pipette, withdraw a 10 cm3 sample of the mixture and transfer it to a conical flask.
4. Stop the reaction by adding a spatula measure of sodium hydrogencarbonate. Note the exact time at which the sodium hydrogencarbonate is added.
5. Titrate the remaining iodine present in the sample with sodium thiosulfate(VI) solution, using starch indicator
6. Continue to withdraw 10 cm3 samples every three mins for 15 using same concen of sodium thiosulfate(VI). Always note the exact time at which the sodium hydrogencarbonate is added.

Question 13

Arrhenius equation practical

Answer 13

-add phenol and bromide solution into one boiling tube and add four drops of methyl red indicator
-add sulfuric acid to another and prepare water bath with 75C and stand two boiling tubes in water bath
-when reached water temp(thermometer) mix contents of two tubes and start stop clock
-leave in water and time until methyl red indicator disappears
-repeat for 65,55,45,35,25 and 15C using ice
(When all phenol has reacted the bromine continuously produced will bleach methyl red)

Question 14

Finding the Ka of a weak acid

Answer 14

-calibrate a pH meter using buffer solution of known pH
-fill burette with sodium hydroxide solution and add 25cm3 of acid being tested to conical flask using pipette and place on white tile
-add few drops of phenolphthalein indicator to conical flask (will be colourless) and carry out titration until solution in conical flask only just turns pink
-add another 25cm3 of weak acid to same flask
-use pH meter to find pH which will equal pKa as exactly half the acid has been neutralised so this is half-equivalence point as [A-]=[HA]
-calculate 10*-pKa to find Ka
-wash pH meter with deionised water between readings to remove ions attached to bulb

Question 15

How to construct electrochemical cells and measure electrode potentials

Answer 15

-clean strips of zinc and copper using sandpaper
-set up zinc half cell by pouring 50cm3 of zinc sulfate solution into 100cm3 beaker and stand strip of copper in beaker
-set up copper half cell by pouring 50cm3 copper(II) sulfate solution into separate 100cm3 beaker and stand strip of copper on beaker
-join beakers with strip of filter paper dipped in potassium nitrate solution
-join the two metal strips with voltmeter using connecting wires and crocodile clips
-record electrode potential on voltmeter, if negative value reverse the connections
-compare with theoretical and repeat for dif combinations of metal/non-metal

Question 16

Making aspirin

Answer 16

1. Weigh 2.0 g of 2-hydroxybenzoic acid and put it in a pear-shaped flask clamped and suspended over beaker of water
2. Add 5.0 cm3 of ethanoic anhydride and five drops of concentrated sulfuric acid to the mixture in the flask. Fix a condenser on the flask.
3. In a fume cupboard, carefully warm the mixture in the water bath using a Bunsen burner. Gently swirl the mixture until all the solid has dissolved and continue warming for another ten minutes.
4. Remove the flask from the hot water bath and add 10 cm3 of crushed ice and some distilled/deionised water to break down any unreacted ethanoic anhydride.
5. Stand the flask in a beaker of iced water until precipitation appears to be complete.
6. Filter off the product using a Bϋchner funnel in flask connected to tap and suction apparatus.
7. Wash the crystals with the minimum volume of iced water.
8. Recrystallise the aspirin in the minimum volume of a mixture of ethanol to water (1 : 3).
9. Filter and dry.
10. Measure the mass of the pure, dry crystals.
11. Measure the melting temperature of the product using melting temperature apparatus

Question 17

Process of recrystallisation

Answer 17

1. Add hot solvent. Add just enough solvent to produce a saturated solution of the impure compound.
2. Filter the hot solution. Remove insoluble impurities by using gravity filtration.
3. Let the solution cool. As the solution cools down, the solubility of the compound decreases.
4. Crystals form. As the solubility of the compound decreases, crystals start to form. As the concentration of impurities is much lower, they take longer to from crystals and hence will remain in solution.
5. Remove the crystals (these are the compound you want). The crystals are removed by using filtration under reduced pressure and then rinsed with cold solvent to remove any soluble impurities. Finally they are let dry using warm oven.