Organic analysis

Question 1

where is the fingerprint reigon on an infrared spectrometry graph

Answer 1

below (to right of) 1500

Question 2

how is infrared spectrometer graph made

Answer 2

different functional groups absorb different wavelengths of IR radiation

Question 3

describe the greenhouse effect

Answer 3

UV wavelength passes through the atmosphere and heats up the earth
The earth emits long wavelength radiation
C=O bonds in CO2 absorb IR radiation so it does not escape the atmosphere
energy is transferred to other molecules through collisons so the atmosphere is warmed

Question 4

how to identify an alkene

Answer 4

add bromine water
positive= turns from orange to colourless

Question 5

identifying aldehydes with fehling’s

Answer 5

Add fehling’s solution and heat
This oxidises the aldehyde into a carboxylic acid and the Cu2+ in fehling’s are reduced to Cu+
positive= red precipitate formed
ketones do NOT react

Question 6

identifying aldehydes with tollen’s

Answer 6

add ammonia and silver nitrate
Silver ions are reduced and a silver mirror forms if test is positive
aldehydes are oxidised to carboxylic acids

Question 7

test for carboxylic acid

Answer 7

add sodium carbonate
fizzing and CO2 gas formed
carboxylic acid becomes a salt with Na+ ions

Question 8

primary and secondary alcohols test

Answer 8

add potassium dichromate and conc. H2SO4
orange to green colour change
alcohols are oxidised

Question 9

what is formed when primary and secondary alcohols are oxidised

Answer 9

primary alcohol will form a carboxylic acid under reflux of aldehyde and seconary alcohol will form a ketone

Question 10

identifying chloroalkane

Answer 10

add acidified silver nitrate and warm
white AgCl precipitate will form

Question 11

how is a H NMR spectra obtained

Answer 11

using samples dissolved in deuterated solvents or CCL4

Question 12

what is the standard used for H NMR and why is this used

Answer 12

TMS (tetramethylsilane)
all protons in same chemical environment (single peak)
non-toxic
unreactive (doesn’t interfere with sample)
volatile (can be easily removed from sample)
absorbs upfield from other protons

Question 13

why is chromatography a good way of separating compounds

Answer 13

each will have a unique affinity for the mobile and stationary phase

Question 14

explain TLC

Answer 14

silica or aluminium oxide spread onto glass/ plastic- stationary phase

organic solvent- mobile phase

Question 15

explain column chromatography

Answer 15

glass column is packed with silica or aluminia

solvent (eluent) is added at the top and substances move down

Question 16

explain gas chromatography

Answer 16

used to separate volatile liquids

long capillary tube is packed with stationary phase- solid or powder coated in oil or other viscous liquid

unreactive gas e.g nitrogen or helium is used as the mobile phase

sample is injected into the capillary tube and put under high heat and pressure

retention times are compared

compounds may be identified using mass spec