Chemical Tests Common Homework Yau-Yan Chai 10P (Flame Tests for Cations,…
Chemical Tests Common Homework Yau-Yan Chai 10P
Test for Sulfate and Carbonate Ions
How to test for Sulfate ions:
If sulfate ions are present, a white precipitate of barium sulfate should form.
First, prepare a sample of the solution which you want to test in a test tube.
Then, add a few drops hydrochloric acid to remove any carbonate ions as they could also create a white precipitate which would give a false positive result.
Next, add a few drops of barium chloride solution. If sulfate ions are present, a white precipitate will form.
How to test for carbonate ions:
Prepare a sample of the solution you want to test in a test tube.
Add a few drops of any dilute acid. If carbonate ions are present, bubbles should begin to form.
If carbonate ions are present, the gas given off by the bubbles should be carbon dioxide. To test for carbon dioxide use limewater. If carbon dioxide is present, the limewater should turn milky white when the gas is bubbled through it.
Test For Halide Ions
How to perform a test for Halide Ions
Prepare of the solution that you want to test in test tube.
add a few drops of dilute nitric acid to the sample
Add a few drops of silver nitrate solution.
Observe and record the colour of any precipitate which forms.
Forms a yellow precipitate
Forms a cream precipitate
Forms a yellow precipitate
if it reignites, oxygen is present as oxygen is one of the components required for fire.
a lightened splint
insert the splint into the test tube, if it makes a squeaky pop, ca
damp litmus paper
turns from red to blue when ammonia is present
this is because ammonia is alkali
damp universal indicator paper
turns red and bleaches
if the water turns from clear to milky white, carbon dioxide is present
Flame Tests for Cations
How Can Flame Tests Be Used in Real Life?
They can be used by geologists to identify metal samples and by forensic scientists to make a quick analysis of the elements present at a crime scene.
produces a red colour
produces a yellow colour
produces a lilac colour
produces a brick red colour
produces a blue-green colour
How to conduct a flame test:
First, dip a clean wire loop into concentrated hydrochloric acid to remove any excess ions on the wire loop.
Then, dip the wire loop into a solid sample of the compound which you want to test
Next, put the loop into the edge of a blue flame on a bunsen burner instead of a yellow flame so that the colour can be seen easier.
Observe and record the colour produced.
Cation tests using sodium hydroxide
How to perform a cation test using sodium hydroxide:
Prepare a sample of the solution which you want to test for cations in a test tube.
Then, add several drops of dilute sodium hydroxide solution to the sample until a precipitate forms.
If a white precipitate forms, continue to add sodium hydroxide and observe the solution to see if the precipitate dissolves.
produces ammonia gas and water
Can be tested using damp red litmus paper. If present, will turn the red litmus paper blue.
forms a blue precipitate
forms a brown precipitate
forms a green precipitate