C4.2
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How do you test for hydrogen?
Hold a lighted splint over the gas , a squeaky pop sound will be made
Test for carbon dioxide
Limewater turns from colourless to cloudy.
What is Limewater and it’s reaction to CO2
Calcium hydroxide solution + carbon dioxide = water + calcium carbonate (white precipitate) Ca(OH)2 + CO2 = H2O + CaCO3(s)
Chlorine test
(Dissolves in water to become acidic.) Dampen blue litmus paper, Should turn red and then white as it bleaches it
Hydrogen test
Place a lit splint in gas, should make a squeaky pop sound
Oxygen test
Glowing splint , should relit
How do we see flame colours
As it burns, the metal ions are vaporised. They absorb energy and the electrons jump to a higher electron shells (excited). As they come back down the energy is emitted off as radiation, visible light in the wave spectrum
How do you conduct a flame test?
• Clean Nichrome wire loop in HCL, hold it in the flame until it stops changing colour. • dip the loop into the test powder. • Hold it in the roaring flame and note the colour
What colour is lithium
Red
What colour is sodium
Yellow
What colour is potassium
Lilac
What colour is Calcium in the flame test?
Orange- Red
What colour is copper
Green - blue
What could be a source of error
Contamination
Why is sodium hydroxide solution used in experiments?
Group 1 hydroxides are soluble in water.
What is the hydroxide precipitate colour of Iron (ll)
Green
What is the hydroxide precipitate colour of Iron (lll)
Orange - brown
What is the hydroxide precipitate colour of copper(ll)
Blue
What is the hydroxide precipitate colour of zinc
White however in excess the zinc hydroxide will dissolve into a colourless solution
What is the reaction for the copper hydroxide test
CuSo4 (aq) + 2NaOH(aq) —> Cu(OH)2 (s) + Na2SO4 (aq) Net ionic equation: Cu 2+ (aq) + OH- (aq) —> cu(OH)2 (s)
What is an anion
A negative ion
What is a cation
A positive ion
How to test for Sulfate ions (SO4 2-)?
• Add HCL • Add barium chloride, BaCl2 • A white precipitate (barium sulphate)forms if sulphate ions are present
How do you test for carbonate ions?
• Add some HCl to solution • If carbonate is present then there is bubbling (the release of carbon dioxide) 2H+ (aq) + CO3 2-(aq) —> CO2 (g) + H2O (l)