Required Practicals

Question 1

In the preparation of ethyl ethanoate, why must concentrated H2SO4 be added slowly and with cooling?

Answer 1

When sulfuric acid is dissolved it gives off a lot of heat which may act as a hazard

Question 2

Why must the mixture in the preparation of ethyl ethanoate be homogenous?

Answer 2

So that the mixture can undergo reflux.

Question 3

Why is concentrated sulfuric acid used in the preparation of ethyl ethanoate?

Answer 3

It acts as a catalyst.

Question 4

What is the function of the solid calcium chloride in the preparation of ethyl ethanoate?

Answer 4

Soaks up any excess eater.

Question 5

What is the nature and purpose of anti-bumping granules?

Answer 5

It prevents bumping (vigorous bubbles)

Question 6

What is reflux?

Answer 6

Continuous boiling and condensing of a reaction mixture.

Question 7

Why is reflux used?

Answer 7

This allows an organic reaction mixture to be heated without losing any reactants or products.

Question 8

What is the purpose of a separating funnel?

Answer 8

To separate into two layers of

• A higher density liquid (typically aqueous) is the bottom layer
• Organic product is the layer above

Question 9

Outline the method involved in using a separating funnel.

Answer 9

1) Place the distillate of impure product into a separating funnel
2) Wash product using either sodium hydrogencarbonate solution or saturated sodium chloride solution
3) Allow layers to separate in funnel, and then run and discard the aqueous layer
4) Run the organic liquid into a clean, dry conical flask and add drying agent (eg anhydrous calcium sulphate)
5) Decant the liquid into the distillation flask
6) Distil to collect pure product.

Question 10

If a sample is pure or impure, what will the melting point be like?

Answer 10

If the sample is very pure the melting point will be sharp (the same value in data books), and if it contains impurities the melting point will be lowered.

Question 11

How do you measure the boiling point of a liquid to determine the purity of it?

Answer 11

• This can be done in a distillation set up or by simply boiling a tube of the sample in a heating oil bath
• Pressure should be noted (as this can change boiling point)
• To get a correct measure the thermometer must be above the boiling liquid, not immersed so it measures the vapour.

Question 12

Describe the method to recrystallisation.

Answer 12

1) Dissolve the impure compound in a minimum volume of (near boiling) solvent
2) filter hot solution through fluted filter paper quickly. (removes any insoluble impurities)
3) Cool the filtered solution by inserting beaker in ice
4) Suction filtrate with a Büchner flask to separate out crystals
5) Wash the crystals with distilled water (to remove soluble impurities)
6) Dry the crystals between absorbent paper (as water would affect yield)

Question 13

Draw a Büchner flask set up.

Answer 13

Question 14

What are some causes for a loss of yield in recrystallisation?

Answer 14

• Crystals lost when filtering or washing
• Some product stays in solution after recrystallisation
• Other side reactions occurring.

Question 15

Draw the set up for gravitational filtration

Answer 15

Question 16

What are some sources of error when measuring an Enthalpy change?

Answer 16

• a heat transfer to or from surroundings
• The method assumes all solutions have the heat capacity of water
• Neglecting the heat capacity of the calorimeter
• Heat absorbed by the calorimeter is absorbed
• Incomplete reaction or dissolving
• Density is taken to be the same as water
• Evaporatjon fo water
• Incomplete combustion

Question 17

How do you improve the accuracy when measuring an enthalpy change?

Answer 17

-An electronic temperature sensor and data logging software could be used to plot the graph accurately
-A flame calorimeter could be used to improve accuracy as
L flame is enclosed
L fuel burns in pure oxygen rather than air
L Spiral chimney is made of copper
-Increase mass of reactants

Question 18

Give the reactions occurring in the iodine clock experiment.

Answer 18

H2O2 + 2H+ + 2I- -> I2 + 2H2O

2S2O3^2- + I2 -> 2I- + S4O6^2-

Question 19

How can we improve the method involved in the iodine clock experiment?

Answer 19

-Use a colorimeter to minimise human error in timing

Question 20

Draw the set up for the iodine clock experiment.

Answer 20

Question 21

Draw a distillation set up

Answer 21

Question 22

How can you test for hydroxide ions?

Answer 22

Using red litmus paper (which turns blue)

Question 23

How can you test for sulfate ions?

Answer 23

By adding barium chloride, which will result in the formation of a precipitate.

Question 24

Draw the set up to test melting point of a compound.

Answer 24

Question 25

Draw the Büchner flask setup

Answer 25

Question 26

Draw how you would use a separating funnel.

Answer 26