QA Flashcards
Possible white solid
- compounds of group 1 and 2 metals
- Zn2+/NH4+ compounds
Colourless solution
solutions of salts of group 1 and 2 metals, Zn2+/NH4+ salts, dilute acids/alkalis, hydrogen peroxide solution
Blue solid/solution
(Solution of) Hydrated Cu2+ salts
Green solid
Fe2+ salts(pale green), CuCO3
Green solution
Solution of Fe2+ salts(pale green)
Yellow solid
Fe3+ salts, AgI(pale yellow), PbI2(bright yellow), ZnO(hot)
Yellow solution
Dilute solution of Fe3+ salts
Brown/Red-brown solid
Fe2O3, Fe(OH)3, Cu(can be pink)
Brown solution
Concentrated solution of Fe3+ salts, i2(aqueous iodine)
Purple solid/solution
KMnO4
Grey solids
Metals except Cu and Au
Black solids
CuO, MnO2, I2(s), carbon powder
Solubility of (SO4)2- salts
All soluble except Ba, Ca, Pb, Ag(sparingly soluble)
Solubility of chloride salts
Soluble except Ag and Pb(except in hot water)
Solubility of carbonate salts
Insoluble except carbonates of group 1 metals and ammonium
Solubility of hydroxides and oxides
All insoluble except group 1 metals, Ba and Ca(slightly)
Test for hydrogen
Colourless, odourless gas evolved extinguishes lighted splint with ‘pop’ sound
Test for oxygen
Colourless, odourless gas relights a glowing splint
Test for carbon dioxide
Colourless, odourless gas evolved forms white precipitate with limewater
Test for ammonia
Colourless, pungent gas turns damp red litmus paper blue
Test for chlorine
Greenish-yellow, pungent gas turns damp blue litmus paper red, then bleaches it
Explanation for test for chlorine(blue litmus turns red then bleach)
Chlorine reacts with water to form mixture of hydrochloric acid and hypochlorous acid. The acids turn damp blue litmus paper red. Hypochlorous acid bleaches the litmus paper
Test for sulfur dioxide
(Use filter paper soaked with KMnO4) Colourless, pungent gas turns acidified potassium manganate(VII) from purple to colourless.
Explanation for sulfur dioxide test
Sulfur dioxide is a reducing agent. It reduces purple manganate(VII) ion to colourless manganese(II) ion
Test for ammonium
NaOH-> colourless, pungent gas evolved, (insert test for NH3)
Test for Ca2+
NaOH -> white ppt, insoluble in excess
Ammonia -> NIL
Test for Al3+
NaOH: white ppt, excess>colourless
NH3: white ppt, insoluble excess
Test for Pb2+
NaOH: white ppt, excess>colourless
NH3: white ppt, insoluble excess
Test for Zn2+
NaOH: white ppt, excess>colourless
NH3: white ppt, excess>colourless
Test for Cu2+
NaOH: blue ppt, insoluble excess
NH3: blue ppt, excess>dark blue
Test for Fe2+
NaOH: green ppt, insoluble excess
NH3: Green ppt, insoluble excess
^ppt turns red brown upon standing
Test for Fe3+
NaOH: red-brown ppt, insoluble excess
NH3: red-brown ppt, insoluble excess
Why no visible change if solution contains Na+ or K+
No reaction between aqueous NaOH or aqueous NH3 and solution containing Na+ or K+
Why do some precipitates dissolve in excess aqueous sodium hydroxide
Ppts can react further with excess alkali to form complex salt that is soluble. White ppts, Al(OH), Pb(OH)2, Zn(OH)2 are amphoteric oxides and ppt further reacts with aqueous sodium hydroxide to form soluble complex salts
Why do some precipitates dissolve in excess aqueous ammonia
Ppts can react further with excess alkali to form complex salt that is soluble. White ppt Zn(OH)2 and blue ppt Cu(OH)2 react with aqueous ammonia to form soluble complex salts
Why ammonia gas produced when aqueous sodium hydroxide is added to a solution with NH4+?
Ammonium salts react with aqueous sodium hydroxide to form soluble salt, water and ammonia gas
Why cant aqueous ammonia be used to test for NH4+
Upon heating, aqueous ammonia itself will produce ammonia gas. In this case, production of ammonia cannot be used to confirm presence of NH4+ in solution
How to differentiate solutions containing Pb2+ and Al3+
Add aqueous solution containing iodide ions/chloride ions/ sulfate ions. Pb+I: bright yellow, Pb+Cl: white, Pb+SO4:white, Ag+any, no visible change
Test for carbonate
Add dilute acids, observation and test for CO2
Test for sulfate
Add dilute nitric acid followed by aqueous barium nitrate. White ppt is seen
Test for chloride
Add dilute nitric acid followed by aqueous silver nitrate. White ppt is seen
Test for iodide
Add dilute nitric acid followed by aqueous silver nitrate. Pale yellow ppt is seen
Test for nitrate
Add aqueous sodium hydroxide followed by aluminium foil and warm. Test gas evolved with damp red litmus paper. (insert observation for ammonia)
Purpose of adding dilute nitric acid before adding test reagent
To remove carbonate ion which may be present in unknown solution as carbonate ion will also react with test reagent to form precipitate
Define thermal decomposition
A chemical process which heat is used to break down a single compound into two or more compounds or elements. A gas is usually produced in the process.
