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Z A Level Chemistry 2 > Organic Synthesis 1 > Flashcards

Organic Synthesis 1 Flashcards

1
Q

What do you need for Quickfit apparatus to carry out an organic preparation?

A
  1. Round bottom or pear shaped flask
  2. Receiver
  3. Screw tap adaptor
  4. Condensor
  5. Still head
    (diagram!)
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2
Q

Why is heating under reflux good?

A
  • Many organic reactions occur slowly at room temp
  • It is common for organic reactions to be heated to overcome the activation energy and increase the rate of reaction
  • Heating under reflux is a common procedure used to prepare an organic liquid without boiling off the solvent, reactants or products
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3
Q

What is heating under reflux?

A

The continual boiling and condensing of a reaction mixture back to the original container to ensure that the reaction takes place without the contents of the flask boiling dry

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4
Q

What do you need for heating under reflux?

A
  1. A round-bottom or pear-shaped flask
  2. Condenser
  3. Rubber tubing
  4. Stand and clamp
  5. Heat source (usually a bunsen burger, tripod and gauze or a heating mantle)
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5
Q

Why is using a Bunsen burner and water bath useful?

A
  • For a reflex experiment using. bunsen burner to heat the reaction mixture allow a reaction under reflux to be carried out at a fixed temperature
  • A water bath can be used if the reaction can be carried out below 100 degrees C
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6
Q

How do you heat flammable liquids?

A
  • A heating mantle can be sued so that there is no naked flame present
  • This provides an added level of safety should any of the apparatus leak or crack
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7
Q

How is the flask clamped?

A

By its neck

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8
Q

What should you do before fitting the condenser?

A

Add the reaction mixture and antibusing granules to the flask

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9
Q

Why are anti-bumping granules added?

A
  • Anti-bumping granules are added to the liquid before the flask is heated so that the contents will boil smoothly
  • If the granules are not used, large bubbles form at the bottom of the liquid and make the glassware vibrate or jump violently
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10
Q

What should you finally add to the ground-glass joint on the condenser?

A
  • Apply a thin layer of grease to the ground-glass joint on the condenser
  • Place the condenser carefully into the flask and gently rotate the condenser back and forth to provide a good seal and ensure that the apparatus comes apart easily a the end of the experiment
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11
Q

What should happen to the condenser during the experiment?

A
  1. During reflux the condenser is kept in the upright position
  2. Condensers should only be clamped loosely as the glass outer jacket is very fragile and is easily broom
  3. Never put a stopped in the top of the condenser as otherwise you would have a closed system and pressure would build up inside as the heated air expanded, which could result in apparatus exploding
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12
Q

Why is rubber tubing added and how does water enter the condenser?

A
  1. Rubber tubing is sued to connect the inlet of the condenser to the tap and the outlet to the sink
  2. Water always enters the condenser at the bottom and leaves at the top to ensure that the outer jacket is full
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13
Q

Why is heating under reflux good?

A
  • Heating under reflux enables a liquid to be continually boiled while the react takes place
  • And this prevents volatile components from escaping the flask boiling dry
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14
Q

What happens to the vapour in the mixture in a reflux?

A

-The vapour from the mixture rises up the inner tube of the condenser until it meets the outer jacket containing cold water
-The vapour then condenses and drips back into the flask
(similar to putting a lid on a saucepan when cooking)

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15
Q

Why is distillation useful?

A
  • Chemical reactions may not go to completion or may produce by products as well as the desired product
  • Once reflux is complete the crude oil or solid product present int eh false needs to be purified to remove any by-products and remaining reactants
  • Distillation is a common method used to separate a pure liquid from its impurities
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16
Q

What do you need to carry out a distillation?

A
  1. Round bottom or pear-shaped flask
  2. Condenser
  3. Rubber tubing
  4. Heat source
  5. Stand and clamp
  6. Screw-cap adaptor
  7. Receiver adaptor
  8. Still head
  9. Thermometer
17
Q

How is the flask clamped in a distillation?

A
  • The flask is clamped by its neck and the still head is connected to the flask
  • The still head adapter is T shaped and has two ground-glass joints, one to fit the screw cap adapter and one to fit the condenser
  • You should grease the joints so the apparatus comes apart easily after the experiment
18
Q

Where and why is a second clamp placed in a distillation?

A
  • A second clamp is placed round the receiver adaptor at the point at which it is attached to the condenser
  • This removes the need to clamp the condenser as it will be supported sufficiently at both ends
19
Q

Why is rubber tubing used in a distillation?

A
  1. As with reflux, rubber tubing is used to connect the inlet of the condenser to the tap and the outlet to the sink
  2. Water always enters the condenser at the lowest point and for distillation this is the closet point to the receiver adaptor
20
Q

Why is a flask used in distillation?

A

To collect the distillate so that the distillation apparatus is not completely airtight

21
Q

What happens in a distillation once the apparatus is set up?

A
  • Once the apparatus is set up, the flask is heated and the mixture In the flask will start to boil
  • The different liquids in the mixture will have different boiling points
  • The liquid with the lowest boiling point is the most volatile and will boil first
22
Q

What happens to the vapour in the distillation?

A
  1. The vapour moves out the flask up into other parts of the apparatus leaving behind the less volatile components of the mixture
  2. When the vapours reach the cold condenser, they condense and become a liquid
  3. The liquid then drips into the collecting flask
23
Q

What might happens when you prepare samples of organic liquids?

A
  • Water may be obtained along with the product
  • If this happened you will see two liquid layers inside your collection flask, one the organic layer and on the aqueous or water layer
  • It is easy to separate these two layers, although you need to know which layer is which to avoid throwing way your product by mistake
24
Q

How do you know which layer is which?

A
  • An easy way to identify the organic later is to add some water to your mixture
  • The layer that gets bigger is the aqueous layer
25
Q

Once the organic layer, has been identified, two are the two layers separated using a separating funnel?

A
  1. Ensure the tap of the separating funnel is closed
  2. Pour the mixture of liquids into the separating funnel, place a stopper in the top of the funnel, and invert to mix the contents
  3. Allow the layer to settle
  4. Add some water to see which layer increases in volume - this is the aqueous layer
  5. Place a conical flask under the separating funnel remove the stopper and open the tap until the whole of the lower layer has left the funnel
  6. Place a second conical flask under the separating funnel to collect the other layer
  7. You will know have one conical flask, costing the organic layer and another containing the aqueous layer, label the flask so that you don’t muddle them
26
Q

How can you purify organic compounds in preparation using acids?

A
  • In preparation using acids, your impure product may contain acid impurities
  • These can be removed by adding aqueous sodium cabinet and shaking the mixture in the separating funnel
27
Q

What will happen to the acid impurities?

A
  • Any acid present will react with sodium carbonate releasing carbon dioxide gas
  • The tap needs to be slowly opened, holding the stoppered separating funnel upside down, to release any gas pressure that may build up
  • Finally the aqueous sodium carbonate layer is removed and the organic layer washed with water before running both layers off into two separate flasks
28
Q

Why is drying the organic product useful?

A
  1. There may be some water left in the organic product

2. Traces of water are removed by adding a drying agent to the organic liquid

29
Q

What is a drying agent?

A

A drying agent is an anhydrous inorganic salt that readily takes up water to become hydrated
-E.G, anhydrous calcium chloride (drying hydrocarbons), anhydrous calcium sulfate (general drying), anhydrous magnum sulfate (general drying)

30
Q

What is the procedure of drying an organic liquid?

A
  1. Add the organic liquid to the conical flask
  2. Using a spatula, add some of the drying agent to the liquid and gently swirl the contents to mix together
  3. Place a stopper on the flask to prevent your product from evaporating away. Leave for about 10 minutes
  4. If the solid has all stuck together in a lump, there is still some water present. Add some drying agent until some solid is dispersed in the solution as a fine powder
  5. Decant the liquid from the solid into another flask. If the liquid is dry it should be clear
31
Q

Describe redistllation

A
  1. Sometimes organic liquid have boiling point that are relatively close together, so your prepared sample may still contain some organic impurities
  2. The distillation apparatus is cleaned and dried and se up again so that a second distillation can be carried out
  3. This time, only collect the product without eh boiling point of the compound you are trying to make
  4. The narrower the boiling range, the purer the product
  5. You now will have separated your product from any impurities
32
Q

What is reflux?

A
  1. Organic reactions are slow and the substance are usually flammable and volatile (they have got low BP)
    - If you sticks them in a beaker and heat them with a Bunsen burner they will evaporate or catch fire before they have time to react
  2. To get around this reflux
  3. The mixture is heated in a flask fitter with a vertical Liebig condenser (this continuously boils, evaporates and condenses the vapours and recycles them back into the flask giving them time to react
  4. The heating is usually electrical (hot plates, heating mantles, or electrical controlled water baths are normally used) and this avoids naked flames that might ignite the compounds
33
Q

What is distillation?

A
  1. Distillation works by gently heating a mixture in a distillation apparatus and the substances will evaporate out of the mixture in order of increasing boiling point
  2. The thermometer shows the boiling point of the substance that is evaporating at any given time
  3. If you know the boiling point of your pure product you can use the thermometer tot ell you when it is evaporating and therefore when it is condensing
  4. If the product of the reaction has a lower bp than the starting material then the reaction mixture can be heated so that the product evaporates from the reaction mixture as it forms
  5. If the starting material has a higher boiling point that the product, so as long as the temperature is controlled, it won’t evaporate out from the reaction mixture
    - Sometime, a product is formed that will go on to react further if it is left in the reaction mixture
    - E.G, iodise primary alcohol, first oxidised to aldehyde and then oxidised to a carboxylic acid, if you want aldehyde product then you can do your reaction in the distillation equipment. The aldehyde product has a lower bp than the alcohol starting material so will distill out of the reaction mixture as soon as it forms and it is then collected in a separate container
34
Q

How can volatile liquids be purified?

A
  • redisdtillation
    1. If a product and its impurities have different boiling points then redistillation can be used to separate them. You just use the same distillation apparatus but this time you are heating an impure product instead of the reaction mixture
    2. When the liquid you want boils (this is when the thermometer is at the bp of the liquid), you placed a false at the open end of the condenser ready to collect your product
    3. When the thermometer shows the temperature is changing, put another flask at the end of the condenser because a different liquid is about to be delivered
35
Q

What does separation do?

A
  • removes any water soluble impurities from the product
  • if a product is insoluble in water than you can use separation to remove any impurities than do dissolve in water such as salts or water soluble organic compounds e.g. alcohols
    1. Once the reaction to form the product is completer, pour the mixture into a separating funnel and add water
    2. Shake the funnel and then allow it to settle. The organic layer and the aq layer (which contains any water soluble impurities (are immiscible), so separate out into two distinct layer
    3. You can then open the tap and run each layer off into a separate container
36
Q

How do you dry your product?

A
  1. If you use separation to purify a product, the organic later will end up counting trace amounts of water so it has to be dried
  2. To do this you can add anhydrous salt such as magnesium sulfate or calcium chloride. The salt is used as a drying agent and it binds to any water present to become hydrated
  3. When you first add the salt to the organic layer it will be lumpy and this means you need to add more and you know that all the water has been remmed when you can swirl the mixture and it looks like a snow globe
  4. You can filter the mixture to remove the solid drying agent

Z A Level Chemistry 2 (17 decks)

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