3:5 Organic analysis

Result of potassium dichromate on all types of alcohols when warmed. How is the colour change formed

Another way to test for alcohols

Primary - orange to green as aldehyde forms

Secondary - orange to green as ketone forms

Tertiary - nothing happens

Colour change is due to orange dichromate (Cr2O7 2-) being reduced to the green chromium ion (Cr 3+)

Using sodium metal. If you add a small piece of sodium to a pure alcohol, it will fix and give offH2 gas.

How tot make Tollens reagent

Why do you get a silver mirror

Add silver nitrate (2cm^-3) then add a few drops of sodium hydroxide solution and a light brown ppt will form. Add drops of dilute ammonia solution until to brown precipitate dissolves completely.

Place the test tube in a hot water bath and add 10 drops of aldehyde and ketone and wait for a few mins to either see nothing (ketone) or a silver mirror forming (aldehyde)

Because the aldehyde reduces the Ag+ ions to silver atoms

How to test for carboxylic acids (or any acid)

They react with carbonates to make a salt, CO2 and water

Add solution and solid sodium carbonate, if it begins to fizz then bubble the gas that is produces through some limewater in a second test tube. This carbon dioxide as will turn the limewater cloudy. If there is no carboxylic acid, nothing happens.

What is high resolution mass spectrometry

Using really accurate atomic masses of atoms to distinguish between similar molecules that have the same mr to the nearest whole number

How does infrared spectroscopy work

How to calc wave number in terms of wavelength

What do they peaks on an infrared spectrum show

A beam of Infrared radiation (IR) is passes through a sample of a chemical, the IR radiation is absorbed by covalent bonds in the molecules, increasing ther vibrational energy. Bonds between different atoms absorb different frequencies of IR radiation. Bonds in different places in a molecule absorb different frequencies too.

1 / wavelength (cm) = wavenumber (cm^-1)

Where radiation is being absorbed

Where is the fingerprint region and what does it show. How can it be used to see purity of a sample.

How is infrared radiation linked to global warming

Between 500-1000 cm^-1 is unique to a particular compound = fingerprint region.

To see purity you can look at the extra peaks in the fingerprint regions as these show impurities.

Some of the electromagnetic radiation emitted by the sun is absorbed and re-emitts some of it as IR radiation. Greenhouse gases such as carbon dioxide, methane and water vapour in the atmosphere absorb the IR radiation and re-emit some back to earth = greenhouse effect. The increase in greenhouse gases is meaning the Earth is warming = global warming