Other Tests Flashcards
How do you test for carbonate CO3 2- and a hydrogen carbonate HCO3 - ?
The basis of the test is that acid plus carbonate equals salt plus water plus carbon dioxide.
To test for this you place a spatula of solid sample in a test tube.
Then you add 2 to 3 cm³ of nitric acid.
Collect any gas given off and bubble through limewater.
A positive test for this is that there is effervescence when the nitric acid is added and then the limewater turns from colourless to milky when tested through limewater.
How do you determine between carbonate and hydrogencarbonate?
You simply dissolve a spatula of the solid sample in 2 to 3 cm³ of water.
then you add 2 to 3 cm³ of magnesium nitrate or magnesium sulphate or even magnesium chloride.
if no precipitate appears immediately heat the contents of the test tube.
A white precipitate should form when the magnesium nitrate is added this confirms carbonate.
If a white precipitate forms on heating then this confirms hydrogen-carbonate.
Testing for halide ions?
Dissolve a spatula of solid sample in 2 to 3 cm³ of deionised water.
add 1 cm³ of nitric acid.
Add a few centimetres cubed of silver nitrate solution.
Add dilute ammonia solution.
Add concentrated ammonia solution
Whenever the silver nitrate solution is added if a white precipitate forms this means that there is a chloride ion.if a cream precipitate forms this means there is a bromide ion.it’s a yellow precipitate forms this means that there is a iodide ion.
When dilute ammonia is added the Cl- precipitate should dissolve. It also dissolves with concentrated ammonia solution.
When dilute ammonia is added the Br- precipitate doesn’t dissolve however dissolves whenever concentrated ammonia is added.
The I- precipitate doesn’t dissolve in either dilute or concentrated ammonia solution.
Testing for barium?
Dissolve a spatula of the solid sample in 2 to 3 cm³ of deionised water.
Add 2-3 cm³ of potassium chromate solution.
add XS hydrochloric acid and shake.
A yellow precipitate should form whenever the potassium chromate is added and whenever and XS dilute hydrochloric acid is added the precipitate dissolves and a yellow solution is formed.
Testing for a copper?
Dissolve a spatula full of the solid sample in 2 to 3 cm³ of the ionised water.
add few drops of dilute ammonia solution.
add XS dilute NH3 solution and Shake.
A blue ppt should form when the dilute NH3 is added and should dissolve to form a dark blue solution whenever XS NH3 is added.
Testing for the ammonium ion.
add a spatula of the solid sample to 3 to 4 cm³ of sodium hydroxide solution.warm this gently.
test with damp red litmus paper or damp universal indicator paper Or test with a glass rod dipped in concentrated hydrochloric acid.
When the solution is warmed a pungent gas should’ve evolved. The paper changes to blue (alkaline gas) and white fumes are formed.
Testing for Fe 2+ / Fe 3+
Fe2+ / Fe3+ :
Dissolve a spatula of solid sample in 2-3cm3 of deionised water. Add a few drops of sodium hydroxide solution. Add XS NAOH solution.
A pale green and a brown ppt should form. The ppts don’t dissolve with XS NAOH.
Fe3+
Dissolve a spatula full of solid sample in 2-3cm3 of deionised water. Test with potassium thiocyanate solution KSCN.
A Blood Red solution forms.
testing for aluminium, zinc and magnesium.
Dissolve a spatula of the solid in 2-3 cm3 of deionised water.
Add a few drops of NAOH.
Add XS NAOH.
ALL FORM A WHITE PPT with a few drops of NAOH. Only magnesium doesn’t dissolve with XS NAOH.
ADD a few drops of NH3 solution.
ADD XS NH3 solution.
All white ppt formed.
IN XS NH3 solution only zinc dissolves.
How do you test for Sulfate SO4 2-?
Firstly dissolve a spatula full of a solid sample in 2 to 3 cm³ of the ionised water.
Then you add 1 cm³ of nitric acid.
Add a few drops of barium chloride BaCl2 solution.
Shake to mix.
The positive result observation should be that a white precipitate forms.
