Summary of Characteristic Reactions of Group Iv Cations

tFind Fe2 +

tFind Fe 3+

tFind Ball 3+

tFind Mn2 +

Solution: Fe 2+ , Fe 3+ , Mn 2+ , Bi 3+ Divide into 4 parts

Corresponding practice diagram: see diagram 3, Part 2. Practice analysis

qualitative

Exercise (Lesson 6)

6.1. Complete the following reaction equations: 1) FeCl 3 + NaOH  ... +....

2) Fe(NO 3 ) 3 + K 4 [Fe(CN) 6 ]  ... +....

3) Fe(NO 3 ) 2 + NaOH  ... +....

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4) FeSO 4 + K 3 [Fe(CN) 6 ]  ... +....

5) Bi(NO 3 ) 3 + Na 2 S  ... +....

6) Bi(NO 3 ) 3 + KI d −  ... +....

7) MnSO 4 + PbO 2 + HNO 3  ... +....

8) MnSO 4 + Na 2 HPO 4  ... +....

9) MgCl 2 + Na 2 HPO 4 + NH 4 OH  ... +....

10) MgCl 2 + NH 4 OH  ... +....

6.3. Can KSCN solution be used to detect the presence of Fe 3+ ions in a solution? Why?

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Lesson 7

Group V cations: Cu 2+ , Hg 2+

Target

4. Describe and explain the reaction of group reagents with group V cations.

5. Write some typical reactions of group V cations.

6. Explain the analysis steps according to diagram 4 (in Lesson 8, section on analysis of group V cations).

1. General properties

- -

Cations of this group are capable of forming stable complexes with NH 3 , CN , SCN ...

The sulfide salts of these cations have different solubilities depending on the acidity of the medium.

Therefore, we can use NH 4 OH to separate the cations of group V, then use Na 2 S to separate each cation in the group.

2. Typical analytical reactions of group V cations

2.1. With NaOH

2 green

Cu 2+ + 2OH - = Cu(OH)

When heated, it forms black CuO Cu(OH) 2 = CuO  black + H 2 O

Cu(OH) 2 is easily soluble in dilute acid and dissolves in NH 4 OH to form a complex.

2+

[Cu(NH 3 ) 4 ] .

2 

brick red

Hg 2+ + OH - = [HgOH] + [HgOH] + + OH - = Hg(OH)

Hg(OH) 2 = HgO  gold + H 2 O

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2.2. With NH 4 OH

4 3 4 2

4 3 4 dark blue 2

Cu 2+ + 4NH OH = [Cu(NH ) ] 2+ + 4H O Hg 2+ + 4NH OH = [Hg(NH ) ] 2+ + 4H O

2.3. With H 2 S or Na 2 S

black

2 black

Cu2 + + HS = CuS + 2H + Cu 2+ + S 2- = CuS 

CuS does not dissolve in HCl, concentrated H 2 SO 4 but dissolves in HNO 3 according to the reaction:

2 black

3CuS + 8HNO 3 = 3Cu(NO 3 ) 2 + 3S + 2NO + 4H 2 O Hg 2+ + HS = HgS + 2H +

black

Hg 2+ + S 2- = HgS 

HgS does not dissolve in HCl, H 2 SO 4 , HNO 3 , but dissolves in aqua regia according to the reaction:

3HgS + 6HCl + 2HNO 3 = 3HgCl 2 + 3S + 2NO + 4H 2 O

HgS is also reduced by SnCl 2 in alkali or oxidized by H 2 O 2 in acidic environment:

HgS + SnCl 2 + 6NaOH = Hg black + Na 2 SnO 3 + Na 2 S + 2NaCl + 3H 2 O HgS + 3H 2 O 2 + 2HCl = SO 2 + HgCl 2 + 4H 2 O

2.4. With Industrial Parks

4

4

Cu 2+ + 4KCN = [Cu(CN) ] 2- + 4K + Hg 2+ + 4KCN = [Hg(CN) ] 2- + 4K +

2.5. With SnCl 2 in NaOH

HgCl 2 + SnCl 2 + 6NaOH = 2Hg black + Na 2 SnO 3 + 4NaCl + 3H 2 O

2.6. With KI

white 2

2  orange red

2Cu 2+ + 4I - = 2CuI + I Hg 2+ + 2I - = HgI

- 2-

HgI 2 + 2I = [HgI 4 ] colorless

2.7. With NH 4 SCN

4 2 black 4

Cu 2+ + 2NH SCN = Cu(SCN) + 2NH +

4 2 white 4

Hg 2+ + 2NH SCN = Hg(SCN) + 2NH +

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If d − NH 4 SCN:

Hg(SCN) 2 + 2NH 4 AD = (NH 4 ) 2 [Hg(SCN) 4 ]

Table 12: Summary of typical reactions of group V cations

Reagents

3. Analysis diagram

+++

Diagram 4*: Theoretical diagram of cations analysis of group V: Hg 2+ , Cu 2+ and group VI: NH 4 , Na , K (See section 3., Lesson 8 below)

Exercise (Lesson 7)

7.1. Complete the following reaction equations: 1) CuSO 4 + NH 4 OH d −  ... +....

2) CuSO 4 + Na 2 S  ... +....

3) Hg(NO 3 ) 2 + KI d −  ... +....

4) Hg(NO 3 ) 2 + NH 4 AD d −  ... +....

7.2. Explain why HgS precipitate cannot be dissolved with HNO 3 solution.concentrated or concentrated HCl? But when on HNO 3and HCl in a 1:3 volume ratio can dissolve HgS?

7.3. Write the reaction of dissolving HgS with H 2 O 2 in an acidic environment.

2+

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Lesson 8

4

Group VI cations: Na + , K + , NH +

Target

1. Write typical reactions to find group VI cations.

2. Explain the analysis steps according to diagram 4 (group VI cation analysis section).

1. General properties

Salts of cations of this group are all soluble, so there is no common reagent for the group. We find each ion directly from the analytical solution (stock solution) thanks to the characteristic reactions of each cation with each specific reagent.

2. Typical analytical reactions of group VI cations

2.1. Find K +

2 6 2 2 6 gold crystals

2K + + Na + + [Co(NO ) ] 3- = K Na[Co(NO ) ] 

+

But NH 4 also gives a similar reaction:

+ + 3-

2NH4​+ Na + [Co(NO 2 ) 6 ] = (NH 4 ) 2 Na[Co(NO 2 ) 6 ] gold crystal

+

Therefore, NH 4 must be removed with alkali and heated, then the solution must be brought to near neutral pH before adding the reagent.

3 2 2

Reaction to find K +hindered by I - ionsand the sensitivity of the reaction increases in the presence of Ag + ions . If I - is presentmust be pre-treated with concentrated HNO or HO

2.1.2. By picric acid

++

++

6 2 2 3 6 4 2 3 gold

K + + CH (NO ) OH = CH (NO ) OK + H +NH 4 + C 6 H 2 (NO 2 ) 3 OH = C 6 H 4 (NO 2 ) 3 ONH 4 Gold + H

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2.1.3. By flame color test: K + gives purple color.

2.2. Find NH 4 +

2.2.1. By strong alkali

+ - 

NH 4 + OH = NH 3 + H 2 O

Recognize NH3 vaporization by using red litmus paper soaked in phenolphthalein solution that turns blue, or paper soaked in phenolphthalein solution that turns red, or by the characteristic ammonia smell.

2.2.2. By Nessler's reagent:

+

In Nessler reagent, NH 4 is converted to NH 3 and gives the reaction: NH 3 + 2K 2 [HgI 4 ] + KOH = [HgI 2 NH 2 ]I reddish brown + 5KI + H 2 O

Some transition metal cations interfere with the above reaction by forming colored hydroxides or destroying the reagents, so they must be removed with strong alkalis and carbonates or locked in a complex with potassium sodium tartrate (KNaC 4 H 4 O 6 ) before using Nessler's reagent.

2.3. Find Na +

2.3.1. By Streng reagent (Zinc Uranyl acetate)

2 3 3 8 3 2 3 3 9 yellow green

Na + + Zn(UO ) (CH COO) + CH COO - = NaZn(UO ) (CH COO)

TT Strength

NaZn(UO 2 ) 3 (CH 3 COO) 9 has ring-shaped crystals when examined under a microscope.

2

2.3.2. Flame color test:

Na + gives a characteristic yellow color.

3. Analysis diagram

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