chemical tests Flashcards
1
Q
cations
A
formed by metal when atoms lose electrons
2
Q
flame tests
A
Li red Na yellow K lilac Ca orange-red Cu blue-green
3
Q
testing compounds with sodium hydroxide
A
- place 1cm3 of salt solution to be tested in test tube
- add drops of 0.5mol/dm3 sodium hydroxide
- add more and record observations
iron(ii)
green/grey precipitate
FeSO4 + 2NaOH —> Na2SO4 + Fe(OH)2
Fe2+ + 2OH- —> Fe(OH)2
iron(iii)
red/brown precipitate
Fe3+ + 3OH- —> Fe(OH)3
copper (ii)
blue precipitate
Cu2+ + 2OH- —> Cu(OH)2
4
Q
test for sulphate and carbonate ions
A
- 1cm3 of solution of unknown substance add 1cm3 of 1mol/dm3 hydrochloric acid
- effervescence = carbonate
-no effervescence then add few drops of barium chloride solution
white precipitate formed = sulphate
5
Q
test for ammonium ions
A
- dissolve spatula of solid in 3cm3 of water
- few drops of sodium hydroxide solution
- damp red litmus = blue ammonia
6
Q
testing for halide ions
A
- measure 1cm3 sample of aqueous chloride into test tube
- add 1cm3 sample of 0.5 mol/dm3 nitric acid
- few drops of silver nitrate solution - forms silver salt (silver chloride)
- repeat with bromide and iodide
AgNO3 + NaCl —> AgCl + NaNo3
silver chloride- white precipitate
Ag+ + Cl- —> AgCl
silver bromide- cream
Ag+ + Br- —> AgBr
silver iodide- yellow
Ag+ + I- —> AgI
7
Q
presence of water
A
cobalt(ii) chloride - blue to pink
anhydrous copper(ii) sulfate- white to blue
