I had a couple of requests for a summary of tests for ions and functional groups. There are series of standard common tests but any reaction in the syllabus that involves an observable change could be used as a ‘test’ to distinguish between two compounds.
The standard tests can be found here in Practical Guide -aqa This is not a list of every reaction that could be used distinguish between compounds though. Almost all the group 2 and group 7 reactions can be used.
How would you distinguish these pairs of compounds?
1. KF (aq) and KCl(aq)
2. KNO3 and AgNO3
3. sodium carbonate and potassium nitrate
4. HNO3 and H2SO4
5. NaCl (aq) and KBr (aq)
6. AgCl (s) and AgI (s)
7. magnesium nitrate and barium nitrate
8. KCl(s) and KI (s) using only conc sulphuric acid
9 propanone and propanal
10. propanoic acid and hexane
11. cyclohexane and cyclohexene
12. butan-2-ol and 2-methylpropan-2-ol
I have a quick question regarding the AQA unit 4 exam tomorrow,
When adding OH- to a buffer, what does it react with and does the concentration of HA:A- remain constant? (and will the model answer for AQA be the same for for both acidic and basic buffers?)
Thank you in advance!
The OH- reacts with the H+ from the equilibrium forming water. The equilibrium shifts to replace the H+. The ratio of HA/A will essentially stay constant though.
It is the same for both acidic and alkaline buffers but the equilibrium equations may look different and shift in different ways.
Acidic is HA –> H+ + A-
alkaline buffer where the equilibrium is CH3CH2NH2 + H+ → CH3CH2NH3+
so acidic shifts equation above shifts right if OH- added and alkaline shifts left if OH- is added