Chemical Analysis - 4.6
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Test for Cl2 - chlorine
Damp blue litmus paper –> white
Test for NH3 - ammonia
Damp red litmus paper –> blue
How to conduct flame test?
Wire into acid Wire into sample Wire into flame Observe flame colour
Flame test: Li +
red
Flame test: Na +
Yellow
Flame test: K+
Lilac
Flame test: Ca 2+
Orange-red
Flame test: Cu 2+
blue-green
Cation - NaOH (sodium hydroxide) tests:
Fe(OH)2 - green Fe(OH)3 - brown Cu(OH)2 - blue
How to conduct NaOH tests?
dissolve sample in water add drops of NaOH observe colour
Test for H2 - hydrogen
Collect a sample of gas in a test tube. Attempt to ignite the gas using a lit splint. Result: squeaky pop sound
Test for O2 - oxygen
Collect a sample of gas in a test tube. Place a glowing splint into the tube. Result: the splint relights
Test for CO2 - carbon dioxide
Bubble a sample of gas through limewater Result: limewater turns cloudy
Chemical test for water
Add anhydrous copper sulphate (CuSO4) Result: goes from white to blue
Physical tests for water
Measure its boiling point - 100 degrees Measure its freezing point - 0 degrees
Test for halides
We test a sample for halide ions (Cl−, Br− and I−) using the Silver Nitrate Test: 1. Dissolve the sample in water. 2. Add nitric acid (HNO3). 3. Add silver nitrate (AgNO3) solution. If Cl−, Br− or I−ions are present, a precipitate forms with the Ag+ ions from the AgNO3
The colour of the precipitate tells you which halide ion (Cl−, Br− or I−) was in the sample:
White - AgCl - Cl- Cream - AgBr - Br- Yellow - AgI - I-
Testing for carbonates
• Add hydrochloric acid (HCl), look for effervescence. • If there is effervescence, bubble the gas through limewater. If CO3 2− ions were present in the sample, the gas evolved turns the limewater cloudy
Testing for sulphates
• Add hydrochloric acid (HCl), look for effervescence. • If there’s no effervescence, add barium chloride (BaCl2) solution. If SO4 2− ions are present, they will form a white precipitate with the Ba2+ ions from the BaCl2
How to conduct the ammonium test?
Dissolve the sample in water. Add some NaOH(aq) and warm it. Test the gas evolved with damp red litmus paper i.e. The Ammonia Test. If NH4 +ions are present in the original sample, the litmus paper will turn blue
How to calculate an Rf value?
Rf = distance moved by spot/distance moved by solvent use a ruler to find measurement if not given