Chemical Tests Flashcards
Test for hydrogen and equation
Gives a squeaky pop with a lighted splint
The hydrogen combusts, reacting with oxygen to form water
2H2+O2 –> 2H2O
Test for oxygen
Relights a glowing splint
Test for Carbon Dioxide and equation
Turns limewater cloudy
Ca(OH)2 + CO2 –> CaCO3 + H2O
Test for chlorine
Bleaches damp litmus paper (it turns red first)
Test for Ammonia
Turns damp red litmus paper blue
Test for water
Turns white anhydrous copper sulphate into blue hydrated copper sulphate
To show the water is pure check that it boils at exactly 100 degrees
flame test: how to do it
Dip wire in concentrated acid and heat in Bunsen to clean it.
Then dip in some acid and then the solid being tested
Then place in blue flame
(Crimson) Red flame =
Lithium
Yellow flame =
Sodium
Lilac flame =
Potassium
Orange red =
Calcium
Sodium hydroxide test: how to do it
Add sodium hydroxide solution to a solution of the unknown compound
Some metal ions will form precipitates of metal hydroxide
NaOH test Blue precipitate
contains copper ions
NaOH test Green precipitate
contains iron (II) ions
NaOH test Orange - Brown precipitate
contains iron (III) ions
Test for ammonium ions: how to do it
Add NaOH solution, if no precipitate forms, warm the solution and test the gas produced with damp red litmus paper (the test for ammonia)
Paper turns blue if positive
Carbonate ions test: how to do it
add dilute acid eg hydrochloric acid to the unknown compound (solid or solution)
if contains carbonate ions then bubbles of CO2 will be produced which turns limewater milky
2H+ + CO3-2 –> CO2 + H2O
Sulphate ions test: how to do it
Add HCl and then barium chloride solution to a solution of the unknown compound (nitric acid and barium nitrate can be used)
Produces a white precipitate = contains sulphate ions
Ba+2 + SO4-2 –> BaSO4
Chloride, bromide, iodide ions (halide ions test)
Add nitric acid and then silver nitrate solution to a solution of the unknown compound
A silver halide precipitate will form
The colour of the precipitate can be used to identify the halide ion present
Results of halide ions test
White precipitate = silver chloride (contains chloride ions)
Ag+ + Cl- —> AgCl
Cream precipitate = silver bromide (contains bromide ions)
Ag+ + Br- —> AgBr
Yellow precipitate = silver iodide (contains iodide ions)
Ag+ + I- –> AgI
Why is acid added in the sulphate and halide negative ions test?
To remove other substances, like carbonate ions, that might form a precipitate and lead to false results
