Organic analysis

How do you test for an ALCOHOL [4 or 3]?

1. 1cm³ of the sample.

2. Add 1cm³ of acidified potassium dichromate solution & shake well.

3. Water bath for 5 min.

Orange solution to green solution.

OR,

1. Add metallic sodium.

Produces hydrogen gas which can be identified by the squeaky pop test.

How do you differentiate between primary, seconday & tertiary alcohols [5]?

• Tertiary = lack of reaction with potassium dichromate.

Use fractional distillation to collect the products made from the oxidation.

• Primary = makes aldehyde.

• Secondary = makes ketone.

Add tollens or fehlings and only the primary presents a positive result.

How do you test for an ALDEHYDE [4 or 4]?

1. 1cm³ of the sample.

2. Add 1cm³ of Fehlings A & B solution.

3. Water bath for 5 min.

Blue solution to brick-red precipitate.

OR,

1. Add 1cm³ of Tollens reagent.

2. Water bath for 5 min.

Grey solution to a silver mirror forms.

How do you test for an ALKENE [3]?

1. 1cm³ of the sample.

2. Add 1cm³ of bromine water & shake well.

Orange solution to colourless solution.

How do you test for an HALOGENOALKANE [4]?

1. 1cm³ of sample.

2. Add 2cm³ of dilute nitric acid.

3. Add 1cm³ of silver nitrate solution.

A silver-halide precipitate forms.

How do you test for a CARBOXYLIC ACID [4]?

1. 1cm³ of sample.

2. Add 1cm³ of sodium hydrogencarbonate solution.

3. Bubble the CO2 produced through limewater.

Turns the limewater milky.

What is MASS SPECTROMETRY & high resolution mass spectrometry?

• Mass spectrometry determines the relative molecular mass of a compound.

• High resolution identifies molecules with the same molecular mass by measuring the relative mass to 4d.p.

What are the isotopes of Cl & Br? And their ‘probabilities'?

→ Chlorine:

Cl³⁵ = 25%

Cl³⁷ = 75%

→ Bromine:

Br⁷⁹ = 50%

Br⁸¹ = 50%

How do you identify a compound from its infrared spectrum?

Use the fingerprinting region to compare the spectrum with spectrums of known compounds to identify the sample. (If there are extra peaks in the fingerprinting region, your sample is impure).

What are the greenhouse gases? How do they contribute to global warming?

• CO2, H2O, CH4.

• Their covalent bonds absorb infrared radiation, re-emit it back to earth and trap the heat.