16 -Organic analysis

Question 1

What is the test for alkenes?

Answer 1

Shake with bromine water
Orange turns colourless.

Question 2

What is the test for halogenoalkanes?

Answer 2

1) Add aqueous NaOH and warm.
2) Acidify with nitric acid
3) Add aqueous silver nitrate (AgNO3)
Precipitate of AgX formed

Question 3

What is the test for aldehydes?

Answer 3

Warm with Fehling’s solution
Blue colour turns to red precipitate

Warm with Tollens’s solution
Silver mirror forms.

Question 4

What is the test for alcohols?

Answer 4

Add acidified potassium dichromate (K2Cr2O7)
Orange colour turns green with primary and secondary alcohols.

Question 5

What is the test for carboxylic acids?

Answer 5

Add sodium bicarbonate (NaHCO3)
Carbon dioxide given off.

Question 6

What is the test for oxygen?

Answer 6

Relights a glowing splint.

Question 7

What is the test for hydrogen?

Answer 7

Ignites a lighted splint with a squeaky pop.

Question 8

What is the test for carbon dioxide?

Answer 8

Turns limewater (calcium hydroxide) cloudy.
Forms calcium carbonate precipitate.

Question 9

What is the test for chlorine?

Answer 9

Bleaches damp litmus paper.

Question 10

Explain mass spectrometry.

Answer 10

The compound enters the mass spectrometer in solution.
It is ionised.
Cations accelerated through the instrument as a beam of ionised molecules.
Hits the detector.

Question 11

What is a mass spectrum?

Answer 11

A graph of relative abundance against mass to charge ratio.

Question 12

What is mass spectrometry used for?

Answer 12

To find the relative molecular mass of organic compounds.

Question 13

What is the molecular ion?

Answer 13

The ion at the highest significant peak on a mass spectrum.

Question 14

What is fragmentation?

Answer 14

Many molecular ions will break up as some of their bonds break as they are ionised so there are ions of smaller molecular mass.

Question 15

What is a fingerprint of a mass spectrum?

Answer 15

When all the fragment ions are used to help deduce the structure of the compound.

Question 16

What is Gas Chromatography Mass Spectrometry?

Answer 16

One of the most powerful analytical techniques used in forensics.

Question 17

How does Gas Chromatography Mass Spectrometry work?

Answer 17

Gas chromatography separates the mixture using a stream of gas to carry the mixture of vapours through a tube packed with a powder solid and the different components emerge at different times.
Their amounts are measured as they emerge and they are fed into a mass spectrometer to produce a mass spectrum of each compound.

Question 18

What is Gas Chromatography Mass Spectrometry used for?

Answer 18

Detecting drugs in athletes and race horses.

Question 19

What is high resolution mass spectrometry?

Answer 19

It measures compounds masses to 3 or 4 decimal places allowing us to work out the molecular formula of the parent ion.
Uses that isotopes don’t have whole number masses.

Question 20

How do atoms joined by chemical bonds act?

Answer 20

The two atoms joined by the bond constantly vibrates.
Stronger bonds vibrate at a higher frequency.
Heavier atoms vibrate at a lower frequency.

Question 21

How does an infrared spectrometer work?

Answer 21

1) A beam of infrared radiation containing a spread of frequencies is passed through the sample.
2) Any particular bond only absorbs radiation with the same frequency as the natural frequency of the bond (which is unique)
3) The radiation that emerges is missing the frequencies that correspond to the types of bonds in the sample.
4) An instrument plots a graph of the intensity of the radiation emerging against the frequency of radiation.

Question 22

What is frequency expressed as for infrared spectrometry?

Answer 22

As a wavenumber measured in cm-1.

Question 23

What does the infrared spectrum look like?

Answer 23

The dips in the graph (called peaks) represent particular bonds.

Question 24

What is infrared spectrometry used for?
(2)

Answer 24

To identify the functional groups present in a compound by identifying particular bonds.
To show the presence of impurities in a pure compound.

Question 25

What is the fingerprint region of an infrared spectrum?

Answer 25

The area of an infrared spectrum below 1500cm-1 which has many peaks caused by complex vibrations of the whole molecule. The area is unique for any particular substance.