3.3.6 Organic analysis

Question 1

How to test for alkenes + what product does it form

Answer 1

add bromine to water
shake
turns colourless if alkene is present
produces dibromoalkane

Question 2

How to test for carboxylic acid

Answer 2

have a flask with a cork and a funnel leading into a test tube filled with limewater

place carboxylic acid into the flask and add carbonate (sodium carbonate solution or solid works)

co2 gas should be produced which gets bubbled through limewater

if limewater turns cloudy then it is a carboxylic acid

(other acids will react the same way so ensure that other test have been dont to narrow down the possibility that it is a carboxylic acid)

Question 3

What is mass spectrometry used to find?

Answer 3

the relative molecular mass (Mr) of a compound

Question 4

What does m/z stand for when reading a mass spectrometry graph

Answer 4

mass/charge

-when molecules are fired through mass spectrometry they are split up into fragments and the mass/charge is the mass of the each fragment divided by its charge (which is +1 as they get ionised at the very beginning)

-because it is mass/1, the m/z ratio is basically just the mass of the fragment

Question 5

On the last fragment peak on a mass spectrometry graph M+1 is written, what does this mean?

Answer 5

the last peak is the M+1 peak/ molecular ion peak, this is the same as the relative molecular mass of the molecule

Question 6

What is high resolution mass spectrometry?

Answer 6

they measure the relative mass to SEVERAL DECIMAL PLACES used

Question 7

When is high resolution mass spectrometry used?

Answer 7

when identifying different molecules with the same molecular mass rounded to the nearest whole number

e.g CH3CHO and C3H8 have the same mass rounded to the nearest whole number (mass spectrometry wouldn’t allow you to identify which of them it would be) But because HRMS measures to several decimal points, you can identify as CH3CHO = 44.0302 and C3H8 = 44.0624

Question 8

What is Infrared spectroscopy

Answer 8

uses infrared radiation to increase the vibrational energy of covalent bonds in a sample (measures the absorptions made by each type of bond in the compound)

Question 9

What 2 things does the frequency of infrared radiation absorbed by a covalent bond depend on?

Answer 9

1. the atoms that are either side of the bond
2. the position of the bond in the molecule e.g OH in alcohol or in carboxylic acid

Question 10

What is the fingerprint region found in a graph from infrared spectroscopy

Answer 10

lies between 500cm-1 and 1500cm-1.

allows us to identify specific molecules (like fingerprints, the size and position fo the peaks are unique to a particular molecule)

Question 11

How do we identify a molecule from its fingerprint region?

Answer 11

compare the fingerprint region generated against a known library of spectra to identify the molecule

Question 12

What do extra peaks in the fingerprint region indicate you have?

Answer 12

impurities in your sample

Question 12

What do extra peaks in the fingerprint region indicate you have?

Answer 12

impurities in your sample

Question 13

How do greenhouse gases cause global warming? (link to bonds)

Answer 13

EM radiation from sun reaches the earth and is absorbed by land and sea. Some is re-emitted as infrared

greenhouse gases, specifically the covalent bonds of the greenhouse gases, ABSORB this radiation and re-emit this back towards the earth (greenhouse effect).

Human activités e.g burning fossil fuels, increase the levels of greenhouse gases in the atmosphere which increases the re-emiting of radiation towards the earth and hence gradual causes global warming