C4.2 Identifying Products Of Chemical Reactions Flashcards
How you can detect carbon dioxide
Test using limewater, mixture of calcium hydroxide solution
Bubbling carbon dioxide through limewater
Goes cloudy white
How you can detect chlorine
Damp blue litmus paper
Paper turns red then white
(Also never say “chlorine ions”, chlorine is an element, “chloride ions”.)
Anion test:
Add few drops of silver nitrate solution and white precipitate should form
How you can detect hydrogen
Lit splint in test tube
Squeaky pop
How you can detect oxygen
Glowing splint relights when put near mouth of the test tube
Flame test
When metal ions are heated energy is transferred to their electrons
This makes them move to higher electron shells
When they move back to their normal electron shells energy is transferred to the surroundings as radiation seen as light
Different metal ions produce different colours of light
Tests for Lithium
Ion: Li+
Flame: Red or crimson
Sodium hydroxide test: N/A
Tests for Sodium
Ion: Na+
Flame: yellow
Sodium hydroxide test: N/A
Tests for Potassium
Ion: K+
Flame: lilac
Sodium hydroxide test: N/A
Tests for Calcium
Ion: Ca2+
Flame: orange-red
Sodium hydroxide test: White precipitate
Tests for Copper(II)
Ion: Cu2+
Flame: green-blue
Sodium hydroxide test: Blue precipitate
Prepare flame test
Clean nichrome wire loop before test by dipping in hydrochloric acid
Rinse with distilled water
Dip clean loop in test powder or solution
Hold above a roaring flame
Clean for each test
What are hydroxide precipitate tests
Group 1 hydroxides are soluble in water but most other metal hydroxides are insoluble
Different metals produce different coloured precipitates
Add a few drops of sodium hydroxide solution to a solution containing metal ions
Tests for iron(ll)
Ion: Fe2+
Flame test: N/A
Sodium hydroxide test: green precipitate
Tests for iron(lll)
Ion: Fe3+
Flame test: N/A
Sodium hydroxide test: orange-brown precipitate
Tests for zinc
Ion: Zn2+
Flame test: N/A
Sodium hydroxide test: white precipitate
What happens when excess sodium hydroxide is added to zinc hydroxide
Zinc hydroxide dissolves to form a colourless solution
Anion test for sulphate ions
Add dilute HYDROCHLORIC ACID to remove any carbonate ions
Then add few drops of BARIUM CHLORIDE solution (BaCl2(aq))
White precipitate if sulfate ions are present
Example: BaCl2(aq) + K2SO4(aq) -> 2KCl(aq) + BaSO4
Ionic equation: Ba 2+(aq) + SO4 2-(aq) -> BaSO4(s)
Anion test for carbonate ions
Add metal carbonate to dilute acid
Bubbles of carbon dioxide gas will be produced
Check by bubbling the carbon dioxide through limewater
Metal carbonate + acid -> salt + water + carbon dioxide
Example: MgCO3(s) + 2HCl(aq) -> MgCl2(aq) + H2O(l) + CO2(g)
Ionic equation: CO3 2- + 2H + -> CO2 + H2O
Anion test for halide ions
Add a few drops of nitric acid
Add few drops of silver nitrate solution (AgNO3(aq))
If chlorine: Cl: white precipitate
If bromine: Br: cream precipitate
If iodine: I: yellow precipitate
Example: NaCl(aq) + AgNO3(aq) -> NaNO3(aq) + AgCl(s)
Ionic equation: Ag +(aq) + X -(aq) -> AgX(s)
Instrumental methods of analysis
Relies on a machine to carry out an analysis of a substance
Can analyse very small amounts of substances if difficult to obtain, very sensitive
Very accurate results, calibrated using international standards
Instruments can carry out analyses quickly and they can run all the time
How do you interpret gas chromatograms
Each peak represents a substance present in the mixture
Areas under each peak show the relative amount of each substance in the mixture
Retention time for a substance to travel through the chromatography column is different for different substances
How do you interpret mass spectra
Can measure masses of atoms and molecules
Used to analyse relative amounts of different isotopes of an element and structure of molecules
Used to detect toxic substances
Harmful as it ionises the sample and breaks it down into fragments
Each peak represents a fragment of the molecule
Peak on the far right represents the molecular ion
Molecular ion peak = relative formula mass of the molecule
