2019 ppq Flashcards
State what is meant by the order of a reaction
The number of species involved in the rate determining step
Name the substance that should be used to set the colorimeter to zero.
Deionised water
The absorbance of the sample solution was 0·71. The sample solution was then diluted to decrease the concentration by half.
The absorbance of this diluted solution was then measured. Explain why the sample solution was diluted.
The absorbance value was outwith the calibration range
State the Brønsted-Lowry definition for a base.
A proton acceptor
Explain why this is a Lewis acid-base reaction.
Water donates (a pair of non- bonding) electrons to B(OH)3
State what caused the electrons to become excited.
Heat
Explain why zinc is colourless
Full 3d subshell
It does not absorb visible light
Explain why the acidified potassium dichromate was added in excess.
To ensure all the ethanol reacted.
Other than apparatus uncertainties and transfer errors, suggest a reason why the experimentally determined concentration of ethanol was higher.
impurities in the vodka may be reacting with dichromate
Carmine can be removed from the reaction mixture by filtration. Suggest how the filtration could be carried out to ensure fast separation.
Under vacuum
Explain how a sigma bond is formed.
End on overlap of (two atomic) orbitals
Explain what is meant by sp2 hybridisation.
Mixing an s (atomic) orbital with two p (atomic) orbitals
Explain fully how this conjugated system gives rise to the red colour of carmine.
Electrons promoted/move from HOMO to LUMO (1)
The complementary colour(s) (to red) is absorbed
Explain why methanol is a suitable solvent for this extraction.
Similar polarities
Explain the effect infrared radiation has on the bonds within molecules and how this allows different functional groups to be identified.
Vibrate/bend/stretch (1) and Different functional groups absorb at different wavenumber
