RP4 - Simple test-tube reactions Flashcards
Testing for halide ions
How would we test for halide ions, what solution would we need?
- Add 2cm3 of dilute nitric acid, followed by 2cm3 of silver nitrate to each sample
- shake gently
presence of chloride ions is show by…?
Presence of Bromide ions is shown by…?
Presence of iodide ions is shown by..?
Chloride = white precipitate
Bromide = cream precipitate
Iodide = yellow precipitate
Why do we add dilute ammonia to each precipitate?
because it is hard to distinguish between the colours sometimes
When we add dilute ammonia to each test tube what will happen?
- Dilute ammonia will cause the white precipitate of ammonia to become colourless
- No change with dilute ammonia for Bromide ions and Iodide ions
What happens when we add Concentrated ammonia to each of the test tubes?
- Bromide ion dissolves to form a colourless solution
- The iodide remains
What do we need to make sure when working with concentrated ammonia?
working in a fume cupboard
Testing for Sulphate ions
What is the test for sulphate ions
Acidified barium chloride
Describe how the test would be carried out?
- using a dropping pipette add equal volumes of Hydrochloric acid and Barium chloride to the sample
What would a positive result show?
A positive result would show a white precipitate of barium sulphate, sulphate ions are present
What are some safety procedure we must follow?
Wear gloves and lab coat because barium chloride is harmful
Testing for Carbonate ions
what is the test for carbonate ions?
Adding HCL and bubble through limewater
Describe how this test would be carried out?
- Add dilute HCL to sodium carbonate solution
- be careful not to touch the sides of the tube with the dropping pipette
- using a a clean pipette collect the gas produced and bubble it through limewater
- place a bung and shake gently from side to side
What is a positive result?
cloudy white mixture
Testing for Ammonium Ions
solutions containing ammonium ions are usually what colour?
They are usually colourless
How would you carry out test to identify ammonium ions?
- Place 10 drops of ammonium chloride into a clean test tube. Add about 10 drops of sodium hydroxide solution. Shake the mixture.
- Warm the mixture in the test tube gently using a water bath. (necessary because ammonia gas is very soluble)
- Test the fumes released from the mixture by using forceps to hold a piece of damp red litmus paper in the mouth of the test tube.
- Make sure the sides of the red litmus paper does not touch the sides of the test tube
What is the observation made?
The red litmus paper turns blue
Why do we mix at the start?
Shaking ensure the reactant
combine properly.
Why is a water bath preferred over a flame?
A water bath is more gentle than using a flame.
Testing for Group 2 ions
What is the test for group 2?
Sodium hydroxide solution
How is the test carried out?
- sodium hydroxide is added to test tubes containing Magnesium, Calcium, Strontium and Barium Chloride
What are the results?
Magnesium forms a Slight white ppt in little NaOH and a white precipitate in excess NaOH
Calcium forms a Slight white ppt
Strontium forms a slight white precipitate
Barium forms a colourless solution with NaOH
Done!!
