Chemical Tests Flashcards
What does Bromine water test for?
Bromine water can be used to distinguish alkenes from alkanes.
Bromine water will change from brown/orange to colourless in the presence of an alkene.
What would you use Potassium Manganate(VII) to test for?
Test for alkenes, a positive result will show a colour change from purple to colourless.
Describe the Silver Nitrate test and what the positive results would show.
Silver Nitrate tests for a halogen in an organic compound.
The test is done by warming the solution with NaOH, then acidifying with dilute nitric acid, then adding the silver nitrate.
Iodine gives a yellow precipitate.
Chlorine gives a white precipitate.
Bromine gives a cream precipitate.
What would you use Potassium Dichromate(VI) to test for and describe a positive result.
When used as an oxidising agent, it changes colour from orange to green with primary and secondary alcohols. Tertiary alcohols cannot be oxidised any further so no reaction occurs and no colour change is observed.
Describe what would be observed in the reaction between sulfuric acid and halide ions
The reaction produces a hydrogen halide.
If the hydrogen halide is exposed to moist air, this can be observed as steamy fumes.
Describe the iodoform (alkaline solution of iodine) test
The test is used to identify a CH3CO group in a compound.
Iodine is added to the sample, followed by just enough NaOH to remove the colour of the iodine.
A positive result is the appearance of a pale yellow precipitate and a “medical” smell.
What does Fehling’s reagent test for and what is the positive result?
Used to test for aldehydes, warm in the presence of a suspected aldehyde and the reagent will change from a dark blue solution to a red-brown precipitate.
Describe the test using Tollen’s reagent and describe a positive result.
Add NaOH to give a precipitate.
Then add dilute NH3 to redissolve the precipitate.
Add the aldehyde or ketone and warm gently.
A ketone will remain colourless, while an aldehyde will form a grey precipitate, or a silver mirror.
What does 2,4 - DNP (2,4-dinitrophenylhydrazine) test for and what is observed with a positive result?
Tests for a C=O bond, so can identify aldehydes and ketones. A positive result will show the formation of an orange/yellow precipitate.
Test for Phenols
Add Bromine to the compound. If a Phenol is present a white precipitate will form.
Alternatively, use aqueous FeCl3, this will change from a yellow solution to a violet solution.
What would you use NaHCO3 to test for?
Used to test for Carboxylic acids, produces carbon dioxide which can be seen as effervescence.
This can be tested by bubbling the gas through lime water, which will turn milky if the gas is CO2
