Practicals AS1

Question 1

How do you determine the formula of a hydrated compound by weighing and heating the salt to constant mass?

Answer 1

1. Weigh and evaporating basin
2. Add some hydrated solid and weigh the evaporating basin and solid
3. Heat to constant mass

Question 2

How do you use deflection of a stream of liquid to show polarity or lack of it?

Answer 2

1. Place a liquid in a burette and place a beaker underneath the jet
2. Open the tap and allow a small stream of liquid to come from the burette
3. Hold a charged polythene rod close to the liquid but not touching and record any deflection
4. To compare polarity use two steams from two burettes simultaneously

Question 3

How do you determine the solubility of chlorine and iodine in aqueous and non aqueous solvents?

Answer 3

1. Add 1cm3 of each of the aqueous halogen solutions into separate test tubes
2. Add equal volumes of saturated hydrocarbon solvent e.g. hexane, shake by stopper and invert
3. Allow two layers to settle and observe colour change

Question 4

How do you produce a reactivity series of the halogens using displacement reactions?

Answer 4

1. Add 1cm3 of each of the aqueous halogen solutions into separate test tubes
2. Ad 1cm3 of potassium chloride to each and record any colour change
3. Repeat with potassium bromide/iodide
4. Starch could be added to detect iodine

Question 5

How do you carry out the reactions of the halides with concentrated sulfuric acid and concentrated phosphoric acid

Answer 5

1. Place 1 spatula of solid potassium chloride in a test tube
2. Add a few drops of concentrated sulfuric acid and record any observations
3. Test the gas evolved
4. Repeat with the rest of the halogens
5. Repeat with concentrated phosphoric acid

Question 6

How do you ensure accuracy when carrying out a titration?

Answer 6

1. Rinse the apparatus with the appropriate solution
2. Add the solution dropwise just before the end point
3. Swirl the flask
4. Read the burette at the bottom of the meniscus

Question 7

How do you carry out a titration?

Answer 7

1. Rinse the pipette with the solution to be transferred to the conical flask
2. Using the pipette and pipette filler transfer 25.0cm3 of the solution into the conical flask
3. Rinse the burette with the solution to be put in it
4. Fill the burette with the bottom of the meniscus on the line
5. Add 3-5 drops of a suitable indicator to the conical flask
6. Add the solution from the burette while swirling the conical flask, record the point where the indicator just changes to two decimal places
7. Repeat to achieve two concordant results

Question 8

How do you prepare a solution of known concentration ?

Answer 8

1. Calculate the mass of solid required for the solution
2. Weigh the solid on a top pan balance in a beaker
3. Dissolve the solid in a small volume of water
4. Transfer the solution to the appropriately sized volumetric flask
5. Rinse the beaker and glass rod with deionised water and add the washing to a volumetric flask
6. Make up to the mark with deionised water and stopper and invert to mix

Question 9

Flame test

Answer 9

1. Dip the nichrome wire into concentrated hydrochloric acid
2. Dip the wire in the test solid
3. Hold the wire in the blue bunsen flame
4. Note the colour of the flame

Question 10

What is the method of preparation of a halogenoalkane?

Answer 10

1. Place 10g of sodium bromide in a pear shaped flask
2. Add 7.5cm3 of Butan-1-ol and 10cm3 of water
3. Lower into a beaker of cold water
4. Add 10cm3 of concentrated sulfuric acid slowly and with stirring
5. Add some anti bump granules
6. Gently reflux the mixture
7. Distill off impure bromobutane
8. Remove unreacted butan-1-ol by shaking with concentrated hydrochloric acid in a separating funnel
9. Dry the impure product
10. Purify the product using simple distillation

Question 11

Draw a diagram for refluxing a halogenoalkane

Answer 11

in book

Question 12

Draw a diagram for the distillation of a halogenoalkane

Answer 12

in book

Question 13

How do you remove acidic impurities using a separating funnel?

Answer 13

1. Place the impure distillate into a separating funnel
2. Add a portion of sodium carbonate solution
3. Stopper and shake
4. Release the pressure at regular intervals by inverting and opening the tap
5. Allow to stand until layers settle and separate, then run off lower layer into a beaker
6. Decide which is the aqueous layer by adding water, whichever increases in size discard

Question 14

How do you dry the product?

Answer 14

1. Place the impure liquid product in a beaker or conical flask
2. Add a spatula of drying agent e.g. Magnesium sulfate
3. Add more drying agent until the liquid is clear
4. Decant the liquid

Question 15

How do you prepare alcohols from halogenoalkanes using alkali

Answer 15

1. Place the halogenoalkane in a pear shaped flask
2. Add dilute sodium hydroxide solution
3. Add some anti bump granules
4. Heat under reflux
5. Distill off the alcohol

Question 16

How do you prepare a carboxylic acid from the corresponding alcohol using acidified potassium dichromate solution

Answer 16

1. Add excess acidified potassium dichromate solution to a pear shaped flask set up for reflux
2. Add antibump granules
3. Add a volume of primary alcohol slowly down the condenser from a dropping funnel, and cool in a water bath
4. Remove the water bath and heat the mixture under reflux
5. Rearrange the acid for distillation and distill if the acid.

Question 17

How do you prepare the aldehyde

Answer 17

1. Add excess acidified potassium dichromate solution to a pear shaped flask
2. Add antibump granules
3. Add a volume of primary alcohol
4. Assemble the apparatus for distillation - this removes the aldehyde from the oxidising mixture immediately and prevents further oxidation

Question 18

How do you prepare the ketone?

Answer 18

1. Add excess acidified potassium dichromate solution to a pear shaped flask set up for reflux
2. Add anti-bump granules
3. Add a volume of secondary alcohol slowly down the condenser from a dropping funnel, and cool in a water bath
4. Remove the water bath and heat the mixture under reflux
5. Rearrange the apparatus for distillation and distill off the ketone.