Chemical tests Flashcards
What is the chemical test to show an alkene?
Add bromine water, the result is the bromine water is decolourised
What is the chemical test used to show the presence of chlorine?
Add sodium hydroxide followed by silver nitrate.
the result is a white precipitate.
What is the chemical test used to show the presence of bromine?
Add sodium hydroxide followed by silver nitrate.
the result is a cream precipitate.
What is the chemical test used to show the presence of iodine?
Add sodium hydroxide followed by silver nitrate.
the result is a yellow precipitate.
What are the chemical tests used to show a primary alcohol?
Add acidified potassium dichromate, and the solution should go from orange to green, then add more potassium dichromate to give a second colour change, from orange to green.
OR
The Lucas test (a solution of saturated and anhydrous zinc chloride) - there will be no change.
Why can you use potassium dichromate twice when testing for a primary alcohol?
Because with the first use the alcohol will oxidise into a aldehyde, and then the aldehyde will oxidise into a carboxylic acid.
What are the chemical tests used to show a secondary alcohol?
Add acidified potassium dichromate, and the solution should go from orange to green, but this only works once.
OR
The Lucas test (a solution of saturated and anhydrous zinc chloride) - the solution goes cloudy after a few minutes.
Why can you use potassium dichromate once when testing for a secondary alcohol?
Because secondary alcohols oxidise into ketones, which cannot be oxidised.
What are the chemical tests used to show a tertiary alcohol?
The Lucas test (a solution of saturated and anhydrous zinc chloride) - the solution goes cloudy instantly
What is the chemical test used to show a carbonyl compound?
Add 2,4-dinitrophenylhydrazine (Brady’s reagent), the result is a yellow/orange precipitate formed.
What are the chemical tests used to show an aldehyde?
Add Tollen’s reagent (ammonia + silver nitrate)
result - silver mirror/black precipitate formed
OR
Add Fehling’s reagent
result - red precipitate formed
What is the chemical test to show the presence of phenol?
Add iron(II) chloride result - orange to purple
What is the chemical test used to show carboxylic acids?
Add sodium hydrogencarbonate and lime water
result - bubbles of gas seen turning the lime water cloudy
What is the chemical test used to show aromatic amines?
Nitrus acid (HNO2) result - Azo dye formed
What is the chemical test used to show aliphatic amines?
Nitrus acid (HNO2) result - bubbles of gas seen.
