Topic 17 - Chemical Testing

Lit splint 2H2 (g) + O2 (g) -> 2H2O (g) Exothermic (combustion)

Squeaky pop Top of the tube resonating and the gas expands quickly through it

Glowing splint Wood + oxygen -> smoke

Relights Oxygen concentration is multiplied by 5, so the rate of reaction increases

Measure MP and BP

MP = 0°C BP = 100°C

anhydrous CuSO4 (s) anhydrous CoCl2 (s)

white (s) -> blue (s) blue (s) -> pink (s)

Bubble through limewater Saturated Ca(OH)2 (aq)

Turns cloudy -> precipitation Ca(OH)2 (aq) + CO2 (g) -> CaCO3 (s) + H2O (l)

Damp blue litmus

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

Damp red litmus Damp because the ammonia gas needs to dissolve to make the colour change

Turns blue NH3 (aq) + H2O (l) -> NH4+ (aq) + OH- OH- is an alkali!

1) add dilute HCl (aq) 2) limewater test 2H+ + CO32- -> CO2 + H2O

Fizzing Limewater turns cloudy

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)

No fizzing White precipitate (barium sulphate) formed

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

White precipitate Ag+ (aq) + Cl- (aq) -> AgCl (s)

Cream precipitate Ag+ (aq) + Br- (aq) -> AgBr (s)

Yellow precipitate Ag+ (aq) + I- (aq) -> AgI (s)

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

Red flame