Organic Techniques

Question 1

Benefits to heating w/reflux

Answer 1

Enables a liquid to be continually boiled without the flask boiling dry/prevents volatile components from escaping

Question 2

Equipment required for reflux

Answer 2

1) round-bottom/pear-shaped flask
2) condenser
3) rubber tubing
4) stand + clamp
5) Bunsen burner + tripod + gauze

Question 3

What if you want to reflux something under 100 degrees c?

Answer 3

Use a water bath

Question 4

How does all the liquid react in a reflux?

Answer 4

Any vapourised liquids rises up and is condensed back into a liquid due to outer jacket containing cold water

Question 5

What is the purpose of distillation

Answer 5

Separation of pure liquids from its impurities

Question 6

Equipment needed for distillation

Answer 6

1) round/pear
2) condenser
3) rubber tubing
4) heat source
5) stand and clamp

6) screw-cap adaptor
7) received adaptor
8) still head
9) thermometer

Question 7

Why does water always enter the condenser at the bottom?

Answer 7

To ensure outer jacket is full

Question 8

How would you remove water from liquid organic products

Answer 8

1) add mixture to separating funnel (ensuring tap is closed) + place stopper + invert to mix
2) allow the layers to settle
3) add some water to find the aq layer
4) place conical flask under funnel + remove lower layer

Question 9

How would you remove acid impurities

Answer 9

1) Add Na2CO3 (aq) + shake separating funnel
2) hold funnel upside down to release CO2 gas
3) remove the Na2CO3 layer
4) wash organic layer w/ water before removing

Question 10

What’s a drying agent

Answer 10

An anhydrous inorganic salt that readily takes up H2O to become hydrated

Question 11

Name 3 common drying agents

Answer 11

CaCl2 - drying hydrocarbons
CaSO4 - general
MgSO4 - general

Question 12

How do you dry an organic liquid

Answer 12

1) add organic liquid + spatula of drying agent to conical flask + swirl
2) place stopper to prevent product from evaporating + leave for 10mins
3) if solid has stuck in a lump = still some water left ∴ add more drying agent until fine powder
4) decant liquid into another flask - should be clear if dry

Question 13

How would you identify whether a substance is pure or not

Answer 13

Find the m.p.

Pure organic substances have v.sharp melting range (1-2degrees)

Question 14

What is the melting range

Answer 14

Difference between T at which sample starts to melt and T at which melting is complete

Question 15

Describe an impure melting range

Answer 15

• wider range

* lower mp than pure sample

Question 16

How do you prepare sample for melting point determination

Answer 16

1) ensure sample is completely dry + free flowing
2) seal a capillary tube by rotating fast in a Bunsen burner
3) cool + fill w/crystals 3mm deep

Question 17

How do you determine mp using electrically heated mp apparatus

Answer 17

1) prepare sample
2) place capillary tube into a sample hole
3) place thermometer in the thermometer hole
4) use rapid heating setting to heat up whilst observing through magnifying window
5) record T at which it starts to melt
6) allow apparatus to cool
7) prepare a 2nd sample + as mp is approached, set low and raise T slowly whilst observing = accurate mp obtained

Question 18

How do you determine mp using thiele tube

Answer 18

1) prepare sample
2) attach capillary tube to thermometer w/ rubber band
3) insert thermometer through hole in cork w/ ends dipped into oil
4) using micro burner, slowly heat side arm of thiele tube
5) record temp and remove heat when all of sample has melted