RP 5 - organic

RP 5

distillation of product from a reaction

preparation of cyclohexene by dehydration and distillation of cyclohexanol

1. pour cyclohexanol into pear shaped flask thats been weighed, reweigh and record mass

2. use plastic graduated dropping pipette to add H2SO4 to flask

3. add anti bumping granules

4. assemble distillation apparatus and heat gently distilling any liquid which boils below 100 degrees

5. pour distillate into separating funnel and add saturated NaCl solution. shake and allow layers to separate

6. run lower level into beaker and transfer upper layer (contains crude cyclohexene) into small conical flask

7. add anhydrous CaCl2 to crude cyclohexene to remove water

8. stopper flask, shake and allow to stand until liquid becomes clear

9. decant into sample container thats been weighed

10. reweigh container, calculate mass produced and determine % yield

testing distillate

use bromine water to confirm alkene - goes colourless

why can the cyclohexene be separated in this way (step 3)

has a lower boiling point

what does saturated NaCl act as

drying agent

what does step 5 do

removes water, a little cyclohexanol and H3PO4

assumption made when calculating mass

all dry distillate is cyclohexene

common mark scheme method

1. acidify potassiu managanate soilution combining volume of it with equal volume of dilute H2SO4

2. pour mixture into pear shaped flask with a still head containing a thermometer

3. attach to condenser with ice cooled collecting vessel

4. add few anti bumping granules

5. heat flask gently

6. collect sample at bp of desired product

7. cooled collection vessel is essential to reduce evaporatation of product

diagram

whys a water bath used

if there are flammable substances present

what do anti bumping granules do

• prevent large bubbles forming

• ensure liquid does not boil too vigorously - mixture would boil over into condenser and undesired impurities would contaminate product

condenser angle

tilted slightly down so any liquid can run into collection flask

where should thermometer bulb be

at the T junction connecting to the condenser to measure the correct bp

condenser water flow

water enters lowest point and leaves highest to go against gravity to

• ensure water fills the condenser (prevents backflow of water)

• maximise heat transfer for condensation (more efficient cooling)

collection flask

must not be sealed to condenser

• system should not be air tight as it is heated the air inside expands

• if air tight the air cannot escape and may cause apparatus to crack

preparation of ethanal by oxidation and distillation of ethanol

1. make oxidising agent by dissolving potassium dichromate in dilute H2SO4 - conc should be 1g in every 10cm3

2. use measuring cylinder to measure it and pour into boiling tube

3. cool in beaker of cold water

4. use teat pipette to add ethanol drop wise shaking to mix contents

5. add anti bumping granules

6. attach to a bung fitted with a right angled glass delivery tube

7. clamp boiling tube in water so delivery tube goes to a test tube immersed in cold water

8. gently heat to slowly distill some liquid distillate

9. use tollens to test

whys cold water used

keep test tube cool to avoid loss of volatile ethanal

tollens silver mirror test

1. add NaOH to AgNO3 in test tube

2. add just enough dilute ammonia solution to dissolve the brown ppt completely

3. using beaker of hot water (50-60 degrees) gently warm in test tube

4. add distillate

5. wait a few mins and record observations - silver mirror should form

safety precautions

• make sure tollens reagent is disposed of thoroughly by rinsing it away with plenty of water

• rinse glassware that has contained reagent with little dilute H2SO4 when finished