Rp 10- Preparation If Organic Solids And Liquids

Question 1

What are the main steps in producing a pure organic solid?

Answer 1

1. Synthesis of the compound (usually using reflux, distillation etc.)
2. Filtration (usually vacuum filtration)
3. Purification (recrystallisation)

Question 2

How do you use lab equipment to heat under reflux?

Answer 2

Quick-fit apparatus Is used to heat a substance under reflux.
- the substance is boiled in a pear-shaped or round bottomed flask
- as it evaporates, it is cooled by the water in the Liebig condenser and so condenses back into a liquid and drips back down into the flask to be heated again.

Question 3

Why is heating under reflux used?

Answer 3

• allows heating for long periods of time
• prevents the flask from boiling dry
• prevents volatile reactants/products escaping
• ensures even heating

Question 4

Why are anti-bumping granules used when heating under reflux and distillation?

Answer 4

To allow smooth boiling- they prevent splashing up the sides of the flask due to bubbles caused by vapours.

Question 5

How do you use lab equipment to filter under reduced pressure?

Answer 5

Using a Büchner funnel and a Büchner flask, connect3d by a rubber tubing to the vacuum source.
- funnel contains a layer of filter paper
- pour the substance onto the filter paper and the liquid will be sucked through via vacuum filtration into the flask.
- the solid will remain on the paper

Question 6

How do you purify s solid product?

Answer 6

Be recrystallisation
- add minimum amount of warm solvent to the impure sample until it has dissolved
- allow to cool, crystals should form
- when no more form you can filter under reduced pressure to obtain a dry crystalline solid.

Question 7

How do you determine the melting point of a substance and why can this info be useful?

Answer 7

• place a small sample of the solid in a capillary tube
• melt using the apparatus available, measuring the temp. with a thermometer
• a pure substance will usually melt at a single temperature (or small range) but an impure substance will melt over a range of temperatures (usually lower than that of the pure substances)
• record the start and end points of the melting
• you can then compare the melting point to known values to identify the substance

Question 8

How do you purify a liquid product?

Answer 8

• use a separating funnel to isolate the organic layer from the aqueous layer
• add anhydrous MgSO4 to the organic product to get rid of all water
• you can then purify the liquid by distillation, which separates the substances by boiling point.

Question 9

How do you calculate the percentage yield of a product?

Answer 9

Actual yield/theoretical yield X 100