Topic 17 - Chemical Testing Flashcards
Hydrogen Test
Lit splint
2H2 (g) + O2 (g) -> 2H2O (g)
Exothermic (combustion)
Hydrogen Result
Squeaky pop
Top of the tube resonating and the gas expands quickly through it
Oxygen test
Glowing splint
Wood + oxygen -> smoke
Oxygen result
Relights
Oxygen concentration is multiplied by 5, so the rate of reaction increases
Test for water that determines purity
Measure MP and BP
Result for water test that determines purity
MP = 0°C BP = 100°C
Tests (2) for water which do not determine purity
anhydrous CuSO4 (s)
anhydrous CoCl2 (s)
Results (2) for water tests which do not determine purity
white (s) -> blue (s)
blue (s) -> pink (s)
Test for carbon dioxide
Bubble through limewater
Saturated Ca(OH)2 (aq)
Result for carbon dioxide test
Turns cloudy -> precipitation
Ca(OH)2 (aq) + CO2 (g) -> CaCO3 (s) + H2O (l)
test for chlorine
Damp blue litmus
Result for chlorine
Turns white (via red because a solution of chlorine is acidic)
Cl2 (g) + H2O (l) -> HCl (aq) + HClO (aq)
Goes white because chloric acid (HClO) acts as a bleach
Test for ammonia
Damp red litmus
Damp because the ammonia gas needs to dissolve to make the colour change
Result for ammonia
Turns blue
NH3 (aq) + H2O (l) -> NH4+ (aq) + OH-
OH- is an alkali!
Test for carbonate
1) add dilute HCl (aq)
2) limewater test
2H+ + CO32- -> CO2 + H2O
Result for carbonate test
Fizzing
Limewater turns cloudy
Test for sulphate
1) do the carbonate test (adding HCl gets rid of any traces of carbonate or sulfite ions which would both produce a precipitate, confusing the results)
2) add a few drops of BaCl2 (aq)
Ba2+ (aq) + SO42- (aq) -> BaSO4 (s)
Result for sulphate
No fizzing White precipitate (barium sulphate) formed
Test for halides
1) add dilute HNO3 (aq) to get rid of carbonate or sulfite ions
2) add AgNO3 (aq)
To provide Ag+, and NO3 prevents false positives because there are no other precipitates
Chloride result
White precipitate
Ag+ (aq) + Cl- (aq) -> AgCl (s)
Bromide result
Cream precipitate
Ag+ (aq) + Br- (aq) -> AgBr (s)
Iodide result
Yellow precipitate
Ag+ (aq) + I- (aq) -> AgI (s)
Describe test for lithium, sodium, potassium, calcium and copper
1) clean a platinum wire loop by dipping it into some dilute HCL
2) dip platinum wire into substance
3) put wire into non-luminous flame
4) check colour
Lithium result
Red flame
