Practicals

Question 1

Finding the Molar Volume of a Gas.
+ diagram +errors

Answer 1

1. Set up the equipment shown in diagram below.
2. Place 30 cm3 (excess) of ethanoic acid in test tube, add pre-weighed marble chips (CaCO3) and quickly place the bung on.
3. Measure the volume of a gas produced with gas syringe.
4. Make a few measurements.
5. Repeat, increasing the mass of the marble chips by around 0.05g each time.
   Errors
   ● If using syringe, plunger may not be free moving. It may need a lubricant.
   ● CO2 is slightly soluble in water, so the exact volume is not measured.
   ● Some gas escapes between addition of marble chips and sealing the test tube.
   ● Bung may not be airtight.

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Question 2

Preparation of a Standard Solution.

Answer 2

1. Weigh out the mass of required acid salt and transfer to a clean beaker.
2. Add 50 cm3 of distilled water to the weighed out solid and stir with a glass rod to dissolve.
3. Using a funnel, transfer to a graduated volumetric flask.
4. Add more distilled water to beaker, add washings to volumetric flask 3 times.
5. Fill volumetric flask with distilled water to the 250 cm3 mark.
6. Stopper the flask, then mix thoroughly by inverting and shaking vigorously.

Question 3

Rates of hydrolysis of halogenoalkanes.
+ expected results

Answer 3

1. Set up 3 test tubes, each with 1 cm3
   of ethanol and two drops of a haloalkane.
2. Place the test tubes in a water bath (60 °C), along with a test tube of 0.1 mol dm−3 silver nitrate and leave all to reach a constant temperature.
3. Quickly add 1 cm3 of a solution of silver nitrate to each test tube containing a haloalkane, and start a stopwatch.
4. Measure and record the time taken for the precipitates to form in each of the test tubes (this is a measure of the rate of reaction).
   - Chloroalkane White precipitate forms slowly.
   - Bromoalkane Cream precipitate forms faster than chloro
   but slower than iodo.
   - Iodoalkane Yellow precipitate forms quickly.

Question 4

Oxidation of ethanol to produce
ethanal and ethanoic acid.

Answer 4

1. Place the acidified potassium dichromate solution in a pear-shaped flask. Cool down the flask using an ice bath.
2. Add a few anti-bumping granules. These will prevent the formation of large gas bubbles that cause violent boiling.
3. Add ethanol dropwise to the pear-shaped flask. Stir to ensure complete mixing.
4. Warm up the flask to room temperature.
5. Set up the reflux apparatus as shown below, placing the flask in a water bath.
6. Heat using the Bunsen burner for 5-10 minutes.
7. Allow some time for the apparatus to cool down. Afterwards, collect the product via distillation using the equipment shown in the diagram below.
   [Use the thermometer to prevent the temperature from rising too high. Keep the bulb in vapours, never in solution.]
8. To preparing an aldehyde, conduct the same reaction under distillation conditions without the reflux process.
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Question 5

Chlorination of 2-methlypropan-2-ol.

Answer 5

1. Add concentrated HCl and the tertiary alcohol to a conical flask. Swirl gently.
2. Put the rubber bung in and swirl the flask gently. Open the bung to release the pressure from fumes from time to time. Repeat this regularly over 20 minutes.
3. Add some anhydrous CaCl2 and shake. At this point, there should be two distinct layers.
   [The upper (organic) layer contains the desired product. The lower layer is the aqueous layer.]
4. Transfer the contents of the flask to separating funnel.
5. Allow the layers to separate and discard the lower (aqueous) layer. Close the tap, keep the organic layer in the separatory funnel.
6. Add a solution of NaHCO3 to remove the unreacted HCl. Swirl gently. Stopper the separating funnel and shake it. Invert the separatory funnel and open the tap to release the pressure due to CO2 formed. Repeat twice.
7. Remove the stopper and run off the aqueous layer. Then, run the organic layer into a clear conical flask. Add some anhydrous Na2SO4 which acts as a drying agent.
8. Swirl the contents and leave the flask to stand for a bit. Then filter it.
9. Distill to purify the product.

Question 6

test for NH4+ ions

Answer 6

● Add aqueous NaOH and gently warm the mixture.
● The ammonia gas will turn moist pH indicator paper blue.
● Pungent smell given off.

Question 7

test for SO4 2− ions

Answer 7

● Add acidified barium chloride solution.
● White ppt forms (BaSO4).

Question 8

Test for bromide

Answer 8

● Add chlorine water to a solution of bromides
● Produces an orange solution if present.
● Some effervescence may be observed.

Question 9

test for alkenes

Answer 9

● Add some bromine water to your compound and shake.
● If there are any C=C bonds, the colour change occurs from orange to colourless.

Question 10

2 ways to test for OH Groups (but not PHENOLS)

Answer 10

● add PCl5
● Misty fumes of HCl produced.

● Add a small piece of sodium.
● Effervescence.

Question 11

test for Carboxylic acids

Answer 11

● litmus paper turns red-ish.
● Add a carbonate/HCO3-
● Effervescence (CO2)

Question 12

Determination of enthalpy change

Answer 12

1. Place one of the reactants into a polystyrene cup and place a thermometer in it.
2. Start a stopwatch and record the temperature of the liquid every minute.
3. At 4 minutes, add the second reactant.
4. At 5 minutes continue taking temperature readings each minute for a further ten minutes.
5. Plot temperatures of a graph and extrapolate to find ∆T.
6. Repeat for the second reaction.