organic chemistry- organic synthesis Flashcards
what is the main purpose of heating under reflux?
so the solution is heated in a controlled manner at a constant temperature without boiling. Heating increases rate of reaction by overcoming activation energy.
to heat under reflux, what equipment do you need?
- pear shaped flask
- condenser
- rubber tubing
- stand and clamp
- heat source (usually Bunsen burner with tripod or heating mantle)
why is a heating mantle used when heating under reflux sometimes?
for heating flammable liquids for providing an extra level of safety in the case of a leak or crack
why can a water bath be used when heating under reflux sometimes?
if the reaction can be carried out below 100 degrees
Before fitting the condenser, add anti-bumping granules to the liquid before it is heated. Why?
so the contents boil smoothly. Without the granules, large bubbles form at the bottom of the liquid and make the glass vibrate.
why should the condenser be clamped loosely?
as it is fragile it may break
why should the stopper not be put at the top of the condenser?
otherwise there will be a closed system and the pressure will increase resulting in an explosion.
why does water always enter the condenser through the rubber tubing?
this allows the water to be continually boiled, preventing any volatile components from escaping and the flask from boiling dry.
why is distillation used after reflux?
to separate a purchase pure liquid from its impurities in the flask.
what apparatus is needed for distillation?
- pear shaped flask
- condenser
- rubber tubing
- heat source
- stand and clamp
- screw cap adapter
- receiver adapter
- still head
- thermometer
how does distillation work?
the different liquids in the mixture have different boiling points. The liquid with the lowest boiling point is most volatile and will boil first. Vapour reaches the condenser and liquid drips into the flask. Less volatile components will be left in the original flask.
sometimes in the collection flask, two liquid layers can be seen, one organic layer and one aqueous or water layer. How do you identify the organic layer?
Add water, the layer that gets bigger is the aqueous layer.
once the organic layer is identified, how do you separate the two layers?
- pour mixture in separating funnel, place stopper
- wait for layers to settle
- add water to identify the aqueous layer
- place a clinical flask under and remove the stopper until the whole layer is left
- place the other layer in another flask
in preparation using acids, how can you remove acid impurities from the product?
add aqueous sodium carbonate. Acid will react forming carbon dioxide gas.
How do you dry the organic compound if water is left in the organic compound?
add a drying agent which is an anhydrous inorganic salt that readily takes up water to become hydrated.
