Testing for ions Flashcards
Ionic compounds needed to be tested for what? What two things do they contain?
Forensic science, +ve and -ve ions
What do flame tests do?
Indentifies metal ions which are positive ions
Why do fireworks contain different metals?
Because they burn in different colours
What colour flame does lithium give? What colour flame does sodium give? What colour flame does potassium give? What colour flame does calcium give? What colour flame does barium give?
Crimson yellow Yellow Lilac Red Green
How do you flame test in a lab?
Dip a clean wire loop into a sample of compound and put it through the blue flame on the BB, before make sure it’s clean by dipping it into HCl and rinsing it in distilled water.
What do some metal ions do?
Form a coloured precipitate with NaOH
What gives hydroxides of metal ions a characteristical colour?
So what experiment do you do to identify the metal ion in a solution?
Metal hydroxides are insoluble so precipitate out of the solution when formed giving the colour
Put some drops of sodium hydroxide into the solution and hope to see the formation of an insoluble hydroxide. You can tell the metal from the colour
What happens in the ionic reaction of calcium in hydroxide? to identify positive ions. Symbol equation:
Ca2+ (aq) + 2OH- (aq) = Ca(OH)2 (s)
What are the colours of the precipitates for the metals in the hydroxide reaction, and their original ions? Calcium Copper (II) Iron (II) Iron (III) Aluminium Magnesium
Ca2+ - white Cu2+ - blue Fe2+ - green Fe3+ - brown Al3+ - white at first but dissolves to colourless Mg2+ - white
If you testing for carbonates what do you test to find?
CO2
If you testing for carbonate ions what do you test to find?
What is the formula for a carbonate ion?
What is the experiment for this?
CO2 CO3(2-) - high 2-, it's the ions charge React the substance with acid, as acid + carbonate = CO2. Bubble the gases given off through lime water and if it's CO2 it will become cloudy
Acid + carbonate =
Salt + water + CO2
What are the halide ions? How do you test for halide ions? What colour precipitate chloride give and it's equation? Bromide Iodide
Halogen ions, chloride etc
Add them to dilute nitric acid HNO3 to acidify, followed by silver nitrate solution (AgNO3)
A white precipitate of silver chloride Ag+ + Cl- = AgCl (s)
A cream precipitate of silver bromide Ag+ + Br- = AgBr
A yellow precipitate of silver iodide Ag+ + I- = AgI (s)
How do you test for sulphate ions (what is the sulphate ion)?
What is the equation?
(SO4 2-) . Add dilute HCl followed by barium chloride solution BaCl2. If a white precipitate of barium sulphate forms it means the original compound was a sulphate.
Ba2+ (aq) + SO4 2- (aq) = BaSO4 (s)
What colour flame does lithium give?
Crimson yellow
What colour flame does sodium give?
Yellow
What colour flame does potassium give?
Lilac
What colour flame does calcium give?
Red
What colour flame does barium give?
Green
Hydroxide reaction precipitate colour: Calcium
Ca2+ - white
Hydroxide reaction precipitate colour: Copper (II)
Cu2+ - blue
Hydroxide reaction precipitate colour: Iron (II)
Fe2+ - green
Hydroxide reaction precipitate colour: Iron (III)
Fe3+ - brown
Hydroxide reaction precipitate colour: Aluminium
Al3+ - white at first but dissolves to colourless
