What are the four flame tests and the results?
Li+ = red
Na+ = Intense yellow
K+ = Lilac
Ca 2+ = Dull orange/brick red
How do you identify an Ammonium ion - NH4+ (test, result and equation)?
Test: Add solution/solid to sodium hydroxide solution. Warm the mixture and test any gas given off with damp red litmus paper.
Result: If ammonium ions are present, pungent smelling gas is produced which turns damp red litmus paper blue.
Equation: NH4+ + OH- —> NH3 + H2O
How to identify metal cations by using precipitation reactions?
- Metal hydroxides are insoluble so can be precipitated from an aqueous solutions of metals salts by adding sodium hydroxide.
- You add the sodium hydroxide a drop at a time to the precipitate.
What are the three metal cations that can be added to sodium hydroxide?
- Copper (ll) ion Cu2+
- Iron(lll) ion Fe3+
- Iron(ll) ion Fe2+
What happens when sodium hydroxide is added to a copper(ll) ion?
- Blue precipitate formed
- Cu2+ + 2OH- —> Cu(OH)2
What happens when sodium hydroxide is added to a iron(ll) ion?
- Moss green precipitate
- Fe2+ + 2OH- —> Fe(OH)2
What happens when sodium hydroxide is added to a iron(lll) ion?
- Foxy red precipitate
- Fe3+ + 3OH—> Fe(OH)3
How do you identify halide ions (anions) by precipitation with silver nitrate solution?
You add to an aqueous solution of the solid being tested some dilute nitric acid, followed by a few drops of silver nitrate solution.
What are the three halide ions (anions) that precipitate with silver nitrate solution and nitric acid?
- Chloride ion Cl-
- Bromide ion Br-
- Iodide ion I-
What happens when silver nitrate solution and nitric acid are added to a chloride ion?
- White precipitate of silver chloride is formed
- Ag+ + Cl- —> AgCl
What happens when silver nitrate solution and nitric acid are added to a bromide ion?
- Cream precipitate of silver bromide is formed
- AgBr+ + Br- —> AgBr
What happens when silver nitrate solution and nitric acid are added to a iodide ion?
- Yellow precipitate of silver iodide is formed
- Agl+ + I- —> AgI
How do you identify sulfate ions - SO4 2- (test, result and equation)?
Test: Add to an aqueous solution of the solid being tested dilute hydrochloric acid followed by a few drops of barium chloride solution.
Result: White precipitate (of barium sulfate)
Equation: Ba2+ + SO4 2- —> BaSO4
How do you identify carbonate ions - CO3 2- (test, result and equation)?
Test: Add to either a solid or an aquesous solution of the solid dilute hydrochloric/ nitric acid.
Result: Bubbles/effervescence seen. Limewater turns milky due to carbon dioxide having been given off.
Equation: CO3 -2 + 2H+ —> CO2 + H2O
How do you do the flame test?
- Dip nichrome wire in concentrated hydrochloric acid, them into solid.
- Hold in blue bunsen burner flame
Why is any acid used?
To get rid of the carbonate and sufite ions before test.
What is the test and result for hydrogen?
Test: Place a lighted splint in mouth of test tube.
Result: Speaky pop sound produced
What is the test and result for oxygen?
Test: Place glowing splint into mouth of test tube.
Result: Splint relights.
What is the test and result for carbon dioxide?
Test: Bubble through limewater.
Result: Limewater turns milky/cloudy.
What is the test and result for ammonia?
Test: Damp red litmus paper
Result: Damp litmus paper turns blue
What is the test and result for chlorine?
Test: Damp blue litmus paper.
Result: Litmus paper turns red then bleaches (white)
