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Flashcards in Prepartaion For Organic Practical Deck (19)
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0
Q

When something is combusted what are the possible observations and what could they mean?

A

It burns with a clear non-smokey flame. Low carbon to hydrogen ratio, could be an alcohol.
It burns with a smokey flame. High carbon to hydrogen ratio. Could be a cyclic alkane or cyclic alkene.

1
Q

What are the only types of compounds they could ask about?

A

Hydrocarbons, alcohols and halogen alkanes.

2
Q

If a substance is added to water, what are the two possible observations and what do they mean?

A

Two layers can form- it does not hydrogen bond with the water.This means a halogen alkane as they don’t have strong dipoles.
It can dissolve fully- it hydrogen bonds with the water meaning a short chain alcohol.

3
Q

How can the C=C bond be tested for?

A

Add bromine water, stopper test tube and shake. If the C=C is present it will go colourless and two layers will form.
Add dilute sulphuric acid then potassium manganate (VII). Shake or put in a beaker of warm water. If C=C present the purple solution will go colourless and two layers will form.

4
Q

How can the OH group be tested for?

A

Add a small piece of sodium or add solid phosphorus chloride and test the gas formed with damp blue litmus paper or a glass rob dipped in concentrated ammonia.

5
Q

If sodium is added to a solution and it contains the OH group, what will happen?

A

Bubbles form and sodium dissolves. A white solid forms in its place.

6
Q

What is the test for alcohol?

A

Add phosphorus pentachloride. It should produce Steamy fumes that turn blue Litmus paper red.
You could also add a dichromate. It should go from Orange to green. This will only happen with primary and secondary secondary alcohol.

7
Q

How do you tell the difference between a tertiary alcohol and other alcohols?

A

Add dilute sulphuric acid and aqueous potassium dichromate (VI) then warm in a beaker of hot water.

8
Q

When testing to find differentiate between tertiary and other alcohols what are the possible observations and what do they mean?

A

The orange solution can turn green meaning it is a primary or secondary alcohol.
It if stays orange it is a tertiary alcohol.

9
Q

How do halogenalkanes react with water?

A

They are insoluble and will form 2 layers.

10
Q

How do you test for the C-Cl, C-Br and C-I group in halogenalkanes?

A

Add ethanol and aqueous silver nitrate and dilute nitric acid. Stand in hot water.
White precipitate= C-Cl group.
Cream precipitate= C-Br group.
Yellow precipitate = C-I group.

11
Q

How can the identity of the halogen in the precipitate formed by adding silver nitrate be found?

A

Add ammonia solution.
Dissolves in dilute ammonia= AgCl a chloroalkane
Soluble in concentrated ammonia= AgBr a bromoalkane
Insoluble in concentrated ammonia= AgI an iodoalkane.

12
Q

How do you oxidise a primary or secondary alcohol?

A

Distill it with sulphuric acid and potassium dichromate (VI) and it will form an aldehyde.
If you heat it under reflux it will form a carboxylic acid.
Water will also form in both instances.

13
Q

What happens when a secondary alcohol is refluxed with an oxidising agent?

A

It will form a ketone and water.

14
Q

What is Brady’s reagent used for?

A

Add it to an aldehyde or ketone and it will give a yellow or orange precipitate.

15
Q

How can aldehydes be tested for?

A

Add Tollen’s reagent and warm. It gives silver mirroring.

Fehling’s solution, which gives a red precipitate on warming.

16
Q

How can an alcohol be dehydrated chemically?

A

Use concentrated phosphoric acid. It will produce an alkene and water.

17
Q

How do you test for an alkane?

A

Burn in oxygen. Should give a blue or yellow flame. If it is sooty, it is a larger molecule.

18
Q

What is the test for carboxylic acid?

A

Add PCl₅. It should produce steamy fumes.

Add an indicator to see if it is acid or alcohol.