3.3.6 Organic Analysis

Question 1

Test-tube reaction identification - alcohols (3)

Answer 1

Acidified potassium dichromate
Primary, secondary - orange to green (dichromate ions reduced to chromium ions)
Tertiary - remains orange

Question 2

Test-tube reaction identification - aldehydes and ketones (2)

Answer 2

Tollen’s reagent - aldehyde gives silver mirror, ketone does not react
Fehling’s solution - aldehyde gives blue liquid to brick-red precipitate colour change, ketone does not react

Question 3

Test-tube reaction identification - carboxylic acids (2)

Answer 3

Solid sodium carbonate

Test any bubbles that are produced in lime water - turns cloudy if a carboxylic acid has released CO2

Question 4

Test-tube reaction identification - alkenes (2)

Answer 4

Bromine water

Decolourises from orange in the presence of double bonds

Question 5

What is mass spectrometry used for?

Answer 5

Determining the molecular formula of a compound

Question 6

What is infrared spectroscopy? (2)

Answer 6

IR radiation is absorbed at different frequencies by different bonds
A spectrometer produces a graph that shows the frequencies of infrared radiation that are being absorbed

Question 7

What is the fingerprint region? (2)

Answer 7

1000 cm^-1 to 1550 cm^-1

The region on an IR spectrum that is unique to a particular compound

Question 8

How can infrared spectroscopy assess purity?

Answer 8

Impurities produce extra peaks in the fingerprint region so a compound can be compared with the spectrum of its pure form

Question 9

How does absorption of IR radiation lead to global warming? (2)

Answer 9

Greenhouse gases (carbon dioxide, methane, water vapour) contains bonds that strongly absorb infrared radiation, trapping it in the atmosphere
The more of these gases there are in the atmosphere, the more IR absorption takes place