QA Post Lab Hand Out Flashcards
- Most _________ are soluble in water; only ____, ____, ____ form chlorides that precipitate from water.
- Thus, the first step in a qualitative analysis is to add about 0.3 F HCl, thereby causing AgCl, PbCl2, and/or Hg2Cl2 to precipitate.
*If no precipitate forms, then these cations are not present in significant amounts. The precipitate can be collected by filtration or centrifugation
- metal chloride salts
- Ag+, Pb2+, and Hg2+2
- metal chloride salts
GROUP 1: INSOLUBLE CHLORIDES
- Next, the acidic solution is saturated with ____.
Only those metal ions that form very insoluble sulfides, such as ____, ____,____,____,____,____,____ precipitate as their sulfide salts under these acidic conditions.
All others, such as ____ and ____, remain in solution. Once again, the precipitates are collected by filtration or centrifugation
- H2S
- As3+, Bi3+, Cd2+, Cu2+, Hg2+, Sb3+, and Sn2+
- Fe2+ and Zn2+
GROUP 2: ACID-INSOLUBLE SULFIDES
group II sulfides
HgS
CuS
Bi2S2
PbS
CdS
group III sulfides
ZnS
CoS
NiS
FeS
MnS
PRECIPITATION of GROUP II and Its Separation into Subgroups IIA and IIB
black
mercuric
bismuth
copper
lead ions
PRECIPITATION of GROUP II and Its Separation into Subgroups IIA and IIB
yellow
arsenic
cadmium
tin ions
PRECIPITATION of GROUP II and Its Separation into Subgroups IIA and IIB
orange
antimony
white turns black
mercury
white suspension
result of the reaction of the sulfide ion with the nitrate ion, in acid solution, to produce result if the reaction pension may appear in the absence of Group II cations.
Aqua regia dissolves HgS by two different types of reactions:
A. the oxidation of the sulfide ion to free sulfur by the nitrate ion
B. the complexing action of the chloride ion to produce the HgCl4 ion.
Aqua regia is composed of:
- 3 parts of concentrated HCI
- one part of concentrated HNO3. A small insoluble residue, after the aqua regia treatment, is free sulfur.
Aqua regia liberates ____ which, if not removed, will oxidize stannous ions to stannic ions
- chlorine
Lead ions are precipitated as PbsO4. However, this precipitate is soluble in the presence of HNO3, because of the formation of _______
**The appearance of dense white fumes of SO, indicates that ______ , has been distilled from the solution
- Pb(HSO4)2
- HNO3
CATIONS II A
- mercury
- lead
- bismuth
- cadmium
- white/gray ppt
- yellow ppt
- black ppt
- yellow ppt
SEPARATION OF GROUPS IIA and IIB
Separation
CENTRIFUGATE FROM GROUP 1: Procedure 3
1. Add 3F HNO3 and heat (water bath)
2. Make barely alkaline (3FNH3) then add 3F HCL until just acid
3. Concentrate to approx. 1 ml + drops HCl + 5 drops of thioacetamide
4. Boil
Procedure 4: SEPARATION OF GROUPS IIA and IIB
1. Ppt from procedure 3 – wash with 10 drops of water +1 drop of thioacetamide + NH4Cl
2. Discard wash water.
3. Add 8 Drops of 3F KOH
4. Stir and water bath
5. Centrifuge and separate
6. centrifugate from residue
7. Residue- treat with 3F KOH and combine the centrifugates
(CONTAINS SULFIDES OF IIA)
Test for Arsenic
The residue is washed
Reason for washing: remove the chloride ion
Unwanted effect: Cl- ion interferes with the confirmatory test for the arsenate ion.
Test for antimony:
Test for antimony:
Test 1: silver coin:
If the coin is not bright, place it in 3 F HNO3 for a few seconds, then pour off the acid and immediately wash with several portions of water.
Test 2: If the arsenic ion is in the solution, it will be deposited as metallic arsenic. However, metallic arsenic is soluble in NaOCI solution and metallic antimony is not.
presence of H2S = darken the coin
Mercuric and cupric ions = cause a black deposit
Gentle rubbing
= black mercury to silvery appearance
= copper to copper-red color
Sodium nitrite oxidizes antimony ions to the pentavalent state
pentavalent antimony apparently oxidizes rhodamine B to produce a color change.
Test for tin:
- magnesium metal is added to reduce the antimony ions completely to the metal
- stannic ions to stannous ions
- appearance of small black flakes = presence of antimony
- magnesium ribbon must be dissolved before making the confirmatory test for tin
- If any magnesium ribbon is left undissolved, a positive test will be obtained, since metallic magnesium reduces mercuric chloride.
