organic synthesis ch 16-28

Why are anti bumping granules added to the flask before refluxing?

To ensure the contents boil smoothly. Without them large bubbles will form and the glassware will vibrate or jump violently.

Why shouldn’t you put a stopper on the top of the condenser when refluxing?

It would create a closed system and the pressure will build up inside as the heated air expands. Could cause the apparatus to explode.

What is distillation used for?

It is a common method used to seperate a pure liquid from its impurities

Why might you need to reflux?

Enables a liquid to continually be boiled whilst reacting. Prevents volitile liquids from escaping and the flask from boiling dry.

How does distillation work?

The different liquids in the mixture will have different boiling points. The liquid with the lowest boiling point is the most volitile and will boil first. Once the vapour reaches the cold condenser, it condenses and becomes liquid again. The liquid will then drip into the collecting glass.

When purifying organic products, how can you distinguish between the organic layer and the aqueous or water layer?

Add water to the mixture. The layer that gets bigger is the aqueous layer.

When preparing organic products using acid, the impure product may contain acids. How can you remove the acid?

Add sodium carbonate. The acid will react and release carbon dioxide. Hold the stoppered serparating funnel upside down and slowly open the tap to release any built up gas pressure.

What might you do if there are still traces of water left in the organic product?

Add the liquid to a conical flask and then add a drying agent to the organic liquid. Gently swirl to mix together. Place a stopper on the flask to prevent the liquid evaptorating and leave 10 mins. If the solid has stuck together in a lump, water may still be present. Add more drying agent until the solid is dispersed in the liquid as a fine powder. Then decant the liquid from the solid into another flask. If the liquid is dry, it should be clear.

What is a drying agent?

An anhydrous inorganic salt that readily takes up water to become hydrated. e.g. anhydrous calcium chloride.

When might you have to preform redistillation?

If the organic liquids have boiling points that are relatively close together, impurities may still remain. Set up a second distillation and only collect the product with the boiling point of the compound you are trying to make. The narrower the boiling range, the pureer the product.