How do we test for Alkenes ?
- Bromine Water
- Add solution and then shake
- Colour change from orange to colourless
How do we test for a Haloalkane ?
How do we test for an Alcohol ?
How do we test for an Aldehyde ?
How do we test for a Carboxylic Acid ?
How does Infrared Spectrometry Work ?
What is the IR Fingerprint region ?
How can the Fingerprint region be used to detect impurities ?
by comparing the spectrum to the pure compound spectrum. Extra peaks show impurities.
How does IR Absorption link with global warming ?
- Q, R, S, T
- (Orange solution) turns green
- P, Q, R, S
- Sweet smelling (liquid)
- To react with (remove excess) acid / neutralise
Describe fully how infrared spectra can be used to distinguish between isomers R, S and T. Use data from Table A in the Data Booklet in your answer (4)
- R & S have an O-H alcohols peak at 3230-3550 cm−1
- T has C=O peak at 1680-1750 cm−1
- R & S (unique) fingerprint region or below 1500 cm−1
- Compare to a database / known spectra (and look for an exact match)
State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers (1)
All have the same Mr
- Named carbonate / hydrogencarbonate / bicarbonate (or Mg / Na)
- No (visible/observed) reaction/change/effect
- effervescence / bubbles (of gas) / fizzing
- Absorption at 1680–1750 cm−1 caused by C=O
- No absorption at 1620−1680 cm−1 caused by C=C
- No absorption at 3230–3550 cm−1 due to −OH (alcohol)
- No absorption at 2500–3000 cm−1 due to −OH (acid)
Explain why determining the precise relative molecular mass of propanal and
prop-2-en-1-ol by mass spectrometry could not be used to distinguish between samples of these two compounds (2)
- have the same molecular formula
- identical / exactly the same / same precise (relative) molecular
OH AND alcohol
No peak / no absorption / no C=O in the range 1680 to 1750 (cm−1) (suggesting no evidence of C=O)
Cyclopentanone
- use fingerprint region
- look for (exact) match to known spectrum
