Organic Analysis

Question 1

What test can be used to test for a carboxylic acid ?

Answer 1

Sodium hydrogencarbonate test
Dissolve NaHCO3 in water, mix carboxylic acid with the solution, and if it is a carboxylic acid it should produce a CO2 effervescence.

Question 2

What test can be used to test for a primary alcohol or secondary alcohol?

Answer 2

In reflux, using acidified potassium dichromate, the solution should turn from an orange solution to a green solution as the alcohol is oxidised.

Question 3

Describe Time of flight mass spectroscopy.

Answer 3

-A Sample is injected using a hypodermic needle
The sample goes through electrospray ionisation or electron impact ionisation to form 1+ ions
-An electric field (using a magnet) accelerates ions so that they all have the same kinetic energy
-they then go through a small hole into the flight tube, and they travel at different speeds and take different times to reach the detector
-as ions hit it at different times, electrons are transferred creating an electric current

Question 4

Describe electrospray ionisation

Answer 4

• Sample is dissolved in a volatile solvent *eg methanol)
• Dissolved sample is injected through a fine hypodermic needle to give a fine mist/aerosol
• tip of the needle is attached to the positive terminal of a high-voltage power supply
• particles are ionised by gaining a H+ ion, forming XH+ ions
• the solvent evaporates

Question 5

Describe electron impact ionisation

Answer 5

• Sample is vaporised, then high energy electrons are fired at sample from an ‘electron gun’
• usually knocks off one electron from each particle forming 1+ ions
• eg X(g) + e- > X+(g) +2e-

Question 6

What equation is used in mass spectroscopy

Answer 6

KE=0.5MV^2
J=0.5xKgx(M/s)^2
All particles have the same energy so heavier particles move slower, and lighter particles move faster

Question 7

How is the time in the flight tube calculated?

Answer 7

T=d/v

Time of flight= distance (m) / velocity (m/s)

Question 8

What does High resolution mass spectrometry not tell us?

Answer 8

It tells us the exact Mr, so therefore the formula but not the compound (due to isomerism)

Question 9

What is TMS?

Answer 9

Tetramethylsaline -used a reference

Question 10

How is TMS suitable for being a reference?

Answer 10

• It has 12 equivalent protons, forming only one peak
• No spin-spin coupling/splitting
• it is inert (doesn’t react)
• it is volatile (doesn’t contaminate the sample)
• it is non-toxic so safe to use
• good shielding

Question 11

What solvents can be used in NMR

Answer 11

D2O
CDCl3
CCl4