Che 21 Equations
Che 21 Equations
Che 21 Equations
litmus stays
red Na+
add 2 drops of dilute no precipitate add NaOH solution, heat,
NaOH solution. NH4+, Na+ test gas with red litmus. litmus goes
blue NH4+
Al(OH)3 + OH → [Al(OH)4]
- -
Pb + 2OH → Pb(OH)2
2+ -
Mg + 2OH → Mg(OH)2
2+ -
precipitate remains add 2 drops, then
Ba + 2OH → Ba(OH)2
2+ -
Mg2+, Ba2+ excess NH3 solution
new sample
Zn + 4NH3 → [Zn(NH3)4]
2+ 2+
→ BaSO4
2+ 2-
Ba + SO4 new sample
Cu + 2OH → Cu(OH)2
2+ -
Cu + 4NH3 → [Cu(NH3)4]
2+ 2+
brown precipitate
brown precipitate forms new add 2 drops, then excess then colourless
Ag+ sample NH3 solution solution Ag+
2Ag + 2OH → Ag2O + H2O
+ -
Ag + 2NH3 → [Ag(NH3)2]
+ +
Identifying Anions CO32−, Cl−, I−, SO42−, NO3−, OH−
bubbles of gas
CO32−
add red litmus litmus goes blue add dilute HCl
OH−, CO32− solution
no bubbles
OH−
white precipitate
add Ba(NO3)2 solution
SO42−
→ BaSO4
2+ 2-
Ba + SO4
no precipitate
new sample
precipitate disappears
Cl−
Ag + 2NH3 → [Ag(NH3)2]
+ +
add AgNO3 precipitate add dilute NH3
solution Cl−, I− solution
Ag + Cl → AgCl
+ -
precipitate remains
Ag + I → AgI I−
+ -
no precipitate
NO3−
Formation of precipitates with either 2 drops of NaOH (or 2 drops of ammonia solution) (*)
Metal ion + hydroxide ion → metal hydroxide precipitate
Al3+ + 3OH- → Al(OH)3 (*) Ba2+ + 2OH- → Ba(OH)2
Zn2+ + 2OH- → Zn(OH)2 (*) Fe2+ + 2OH- → Fe(OH)2
Pb2+ + 2OH- → Pb(OH)2 (*) Fe3+ + 3OH- → Fe(OH)3
Mg2+ + 2OH- → Mg(OH)2 Cu2+ + 2OH- → Cu(OH)2 (*)
White hydroxide precipitates that dissolve in excess NaOH forming complex ions
Metal hydroxide + hydroxide ion → soluble complex ion
M(OH)X + yOH- → [M(OH)4]y-
x + y = 4
Al(OH)3 + OH- → [Al(OH)4]-
Zn(OH)2 + 2OH- → [Zn(OH)4]2-
Pb(OH)2 + 2OH- → [Pb(OH)4]2-
Precipitates that dissolve in excess ammonia solution
Precipitates of zinc hydroxide, copper hydroxide, silver oxide** and silver chloride**
Zn2+ + 4NH3 → [Zn(NH3)4]2+
HINT BOX
Cu 2+
+ 4NH3 → [Cu(NH3)4] 2+
Write the equations for formation of
Ag + 2NH3 → [Ag(NH3)2] (** same equation)
+ +
precipitates backwards
• Product
• Reactants
Test to confirm Fe3+ • Balance it
Eg → Pb(OH)2
Fe3+ + SCN- → FeSCN2+ Or write as [FeSCN]2+ Pb2+ + OH- → Pb(OH)2
Pb2+ + 2OH- → Pb(OH)2
Test to identify barium ion / test to identify sulfate ion Write the equations for formation of
Ba2+ + SO42- → BaSO4 (yes – the same equation!) the complexes backwards
• Product
Test to identify lead ion • Reactants
• Balance it
Pb2+ + SO42- → PbSO4 Eg
→ [Cu(NH3)4]2+
Cu2+ + NH3 → [Cu(NH3)4]2+
Test to identify chloride or iodide ion
Cu2+ + 4NH3 → [Cu(NH3)4]2+
Ag+ + Cl- → AgCl Ag+ + I- → AgI