Qualitive analysis Flashcards
Testing for an alkene? What reaction is taking place?
Addition of bromine water Br2 (aq) , will result in the decolourisation of a brown liquid. Addition.
What is the first step in the test for a haloalkane?
The reaction of the given haloalkane with NaOH in a mixture of ethanol and water (warm), will result in the halogen being released into solution.
What can then be used to test for the specific halogen?
React the solution with HNO3, followed by the addition of AgNO3. Silver halides will form if present.
Why is the acidification step done?
Will remove carbonate ions that could give a false read.
What colours will form with the silver halides? Order of reactivity?
Chloride: White (Fastest)
Bromide: Cream
Iodide: Pale yellow (Slowest)
What last test can be used to check for a halide? Concentrated or dilute?
Ammonia will allow distinction:
AgCl will disolve in dilute
AgBr will disolve in conc
AgI will be insoluble in conc
How can you test for a carbonyl? What will occur?
2,4-DNP or Bradys reagant followed by a few drops of sulfuric acid. Pale orange solution (2,4-DNP), if you add ketone or aldehyde then orange precipitate will form.
How can you differentiate between a ketone or aldehyde? What is added? What happens?
Addition of tollens reagant, warmed. If aldehyde then it will be oxidised to carboxylic acid, and Ag+ ions will be reduced to Ag. A silver mirror will be formed.
What is Fehlings solution?
Addition of solution containing a an aldehyde will change Fehlings solution from Blue to brick red precipitate.
What can be used to test for an alcohol?
Addition of oxidising agent such as K2Cr2O7/H+ to the alcohol.
Place in hot water bath at about 60°c
If primary or secondary then will be oxidised and turn from orange to green.
How can test for a carboxylic acid? 2 Ways.
Can either check the pH which shoud be about 3.
Or,
Addition of Na2CO3 will result in the formation of CO2 whcih can then be checked by lime water test.
