Inorganic Chemistry (Qualitative Analysis)

Group I (Silver/Chloride) cation precipitant

2M/3M HCl or any soluble chloride salt.

Group I cations

Ag+, Pb2+, Hg2^2+.

Group II (Cu-Tin) cation precipitant

H2S; adjust H+ to 0.3 M and saturate with H2S.

Group II Cu subgroup

Cu2+, Cd2+, Pb2+, Bi3+; insoluble in Na2S.

Group II Tin subgroup

Hg2+, As3+/As5+, Sn2+/Sn4+, Sb3+/Sb5+; soluble in Na2S.

Group III (Al-Fe) precipitant

(NH4)2S or NH4Cl, NH3, and H2S.

Group III Al subgroup

Al3+, Cr3+, Zn2+; soluble in NaOH and Na2O2.

Group III Fe subgroup

Fe2+/Fe3+, Mn2+, Ni2+, Co2+; insoluble in NaOH and Na2O2.

Group IV (Alkaline Earth) precipitant

NH3, NH4Cl, (NH4)2CO3, and 95% C2H5OH.

Group IV cations

Ba2+, Sr2+, Ca2+, Mg2+.

Group V (Alkali) precipitant

None.

Group V cations

K+, Li+, Na+, NH4+.

Ag+ + NH4OH

AgOH; white precipitate.

Ag+ + excess NH4OH

Ag(NH3)2+; soluble, colorless solution.

Cu2+ + NH4OH

Cu(OH)NO3; green basic salt.

Cu2+ + excess NH4OH

Cu(NH3)4+ or Cu(NH3)4(OH)2; soluble blue solution.

Al3+ + NH4OH

Al(OH)3; white gelatinous precipitate.

Cr3+ + NH4OH

Cr(OH)3; grayish-green precipitate.

Zn2+ + NH4OH

Zn(OH)2; white precipitate.

Zn2+ + excess NH4OH

Zn(NH3)4^2+; soluble colorless solution.

Mn2+ + NH4OH

MnO2·H2O; white to light-brown precipitate.

Fe3+ + NH4OH

Fe(OH)3; reddish-brown precipitate.

Fe2+ + NH4OH

Fe(OH)2; white to green to brown precipitate.

Co2+ + NH4OH

Co(OH)NO3; blue basic salt.

Co2+ + excess NH4OH

Co(NH3)4^2+; soluble dirty-yellow solution.

Ni2+ + NH4OH

Ni(OH)NO3; green basic salt.

Ni2+ + excess NH4OH

Ni(NH3)4^2+; soluble blue solution.

Ag+ + NaOH

AgOH → Ag2O; white to brown precipitate.

Pb2+ + NaOH

Pb(OH)2; white amorphous precipitate.

Pb2+ + excess NaOH

Pb(OH)4^2− or Na2PbO2; colorless solution.

Hg2+ + NaOH

HgOH → Hg2O; black precipitate.

Al3+ + NaOH

Al(OH)3; white gelatinous precipitate.

Cr3+ + NaOH

Cr(OH)3; grayish-green precipitate.

Cr3+ + excess OH−

NaCrO2; soluble green solution.

Cr3+ + Na2O2 or H2O2

Na2CrO4; yellow solution.

Zn2+ + NaOH

Zn(OH)2; white precipitate.

Zn2+ + excess NaOH

Na2ZnO2; soluble colorless solution.

Mn2+ + NaOH

Mn(OH); white precipitate.

Mn2+ oxidized with Na2O2 or H2O2

MnO2·H2O; brown precipitate.

Fe3+ + NaOH

Fe(OH)3; reddish-brown precipitate.

Fe2+ + NaOH

Fe(OH)2; white to green to brown precipitate.

Fe2+ + Na2O2 or H2O2

Fe(OH)3; reddish-brown precipitate.

Co2+ + NaOH

Co(OH)2; blue precipitate on warming, pink precipitate.

Co2+ + Na2O2 or H2O2

Co(OH)3; brown or black precipitate.

Ni2+ + NaOH

Ni(OH)2; apple-green precipitate.

Ni2+ + H2O2

Ni(OH)3; green precipitate; no oxidation with Na2O2.

Pb2+ + H2S

PbS; black precipitate.

Bi3+ + H2S

Bi2S3; dark-brown or brownish-black precipitate.

Cu2+ + H2S

CuS; black precipitate.

Cd2+ + H2S

CdS; yellow precipitate.

Hg2+ + H2S

HgS; white → yellow → brown → black precipitate.

Hg2+ + H2S, then Na2S

Na2HgS2; soluble in Na2S, colorless solution.

Sb3+ + H2S

Sb2S3; orange or reddish-orange precipitate.

Sb3+ sulfide in excess Na2S

Na3SbS4; soluble in Na2S, colorless solution.

As3+ + H2S

As2S3; yellow precipitate.

As sulfide in excess Na2S

Na3AsS4; soluble in Na2S, colorless solution.

Sn2+ + H2S

SnS; light-brown precipitate.

Sn2+ sulfide in Na2S

Na2SnS3; soluble in Na2S, colorless solution.

Sn4+ + H2S

SnS2; yellow precipitate.

Sn4+ sulfide in Na2S

Na2SnS3; soluble in Na2S, colorless solution.

Al3+ + NH4Cl/NH4OH

Al(OH)3; white gelatinous precipitate.

Al3+ + (NH4)2S

Al(OH)3; white gelatinous precipitate.

Cr3+ + NH4Cl/NH4OH

Cr(OH)3; grayish-green precipitate.

Cr3+ + (NH4)2S

Cr(OH)3; grayish-green precipitate.

Zn2+ + NH4Cl/NH4OH

Soluble.

Zn2+ + (NH4)2S

ZnS; white metallic precipitate.

Mn2+ + NH4Cl/NH4OH

Soluble.

Mn2+ + (NH4)2S

MnS; flesh or salmon precipitate.

Fe3+ + NH4Cl/NH4OH

Fe(OH)3; reddish-brown precipitate.

Fe3+ + (NH4)2S

Fe2S3; black precipitate.

Fe2+ + NH4Cl/NH4OH

Soluble.

Fe2+ + (NH4)2S

FeS; black precipitate.

Co2+ + NH4Cl/NH4OH

Soluble.

Co2+ + (NH4)2S

CoS; black precipitate.

Ni2+ + NH4Cl/NH4OH

Soluble.

Ni2+ + (NH4)2S

NiS; black precipitate.

Ba2+ flame test

Yellowish-green.

Sr2+ flame test

Crimson or carmine red.

Ca2+ flame test

Brick red or dull red.

Mg2+ flame test

Colorless.

K+ flame test

Violet.

Na+ flame test

Intense yellow.

Li+ flame test

Crimson or carmine red.

Purpose of cobalt glass in flame test

To prevent the interference of sodium.

Na flame through cobalt glass

Golden-yellow flame becomes nil/absent.

K flame through cobalt glass

Violet flame becomes crimson.

Ca flame through cobalt glass

Brick-red flame becomes light-green.

Sr flame through cobalt glass

Crimson flame becomes purple.

Ba flame through cobalt glass

Yellowish-green flame becomes bluish-green.

Ag+ confirmatory test with HCl

AgCl; white curdy precipitate that becomes gray when exposed to light.

Ag+ with excess NH3

Colorless solution.

Ag+ confirmatory test with K2CrO4

Ag2CrO4; brownish-red precipitate.

Ag+ confirmatory test with KI

AgI; canary-yellow precipitate.

Pb2+ with HCl

PbCl2; soluble in boiling water.

Pb2+ confirmatory test with K2CrO4

PbCrO4; yellow precipitate.

Pb2+ with excess NaOH

Na2PbO2; yellow solution.

Pb2+ confirmatory test with KI

PbI2; yellow precipitate.

Hg2^2+ with HCl

Hg2Cl2; white curdy precipitate.

Hg2^2+ with excess NH3

HgNH2Cl and HgO; white and black precipitate.

Hg2^2+ confirmatory test with K2CrO4

Hg2CrO4; orange-red precipitate, becoming brownish-red on boiling.