2019 Flashcards
Which of the following techniques could be used to purify an impure sample of solid caffeine?
recrystallisation
Describe a suitable control experiment that could be used to validate this technique.
Use a known concentration/standard
solution of ethanol
Describe fully how this 0·010moll−1 solution should be prepared in a
50 cm3 volumetric flask from the 0·10 mol l−1 stock solution.
- 5 cm3
- procedure involving pipette/
burette and making up to the mark
A complexometric titration can be used to determine the concentration of
calcium ions in milk
Explain fully why a solution of the complex ion [Zn(H2O)6]2+ is colourless.
- Full d sub shell so no d-d
transitions possible - It only absorbs ultraviolet/UV light
how do sigma bonds arise
end on overlap of orbitals
Other than apparatus uncertainties and transfer errors, suggest a reason why the experimentally determined concentration of ethanol was higher
Other ingredients in the
vodka may be reacting with
dichromate
Explain fully how this conjugated system gives rise to the red colour of carmine.
- Electrons promoted from
HOMO to LUMO - The complementary colour is absorbed
Explain why methanol is a suitable solvent for this extraction.
volatile
Explain the effect infrared radiation has on the bonds within molecules and how this allows different functional groups to
be identified.
- bend and stretch
- Different /functional groups
absorb at different wave numbers
State what is meant by the term optical isomers.
Non-superimposable mirror images of each other
Methoxide ions can be produced by reacting sodium with a reagent.
Name the reagent.
methanol
Suggest why this reaction is more likely to proceed by an SN1 mechanism rather than an SN2 mechanism.
Formation of a stable (tertiary)
carbocation
