cations separation exp

8/11/2019 Cations Separation exp

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1Academic Year

A14


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Contents Page

Preface 3

General instruction to the students 4

Basic tools 5

Before coming to laboratory 6

Experimental procedure 7

Preparation of the salt solution 9

Classification of cations 10

Group I 11

Report sheet 14

Group IIA 17

Report sheet 20

Group IIB 23

Report sheet 24

Group III 27

Report sheet 29

Group IV 32

Report sheet 34

Group V 37

Report sheet 39

Group VI 42

Report sheet 44

Test of ammonium 46

Report sheet 47

Scheme for identification of basic radical in mixture 48

General questions 50

Contents


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Preface

etals are a very important part of our society and the majority of

these are not found in the metallic form in nature. The more

useful metals (including copper, nickel, zinc, etc.) occur as

positively charged ions (cations) incorporated into minerals. The

cations of the more useful metals are often mixed with an array of less valuable

cations. Separation of the cations of the desired metal from the others is a

critical step in metal production. This experiment will explore some of the

strategies used to separate (and identify) metal cations. The term analysismeans the identification of the components in a substance. When the term

qualitative is used, it means that only visual observation are required. Not

include information about the quantity of the component in question is obtained.

Qualitative analysis is possible because experience has shown that

certain chemical reactions of ions in solution are limited to at most a few kinds

of ions. Some reactions are unique to a specific ion. If we conduct an experiment

in such a way that a positive reaction is possible for only one kind of ion, we can

get a yes or no answer to the presence of the ion in question. The separation

and qualitative analysis of a large number of the common cations is based on the

selective solubilities of the compounds of the cations. Qualitative analysis is a

method used for identification of ions or compounds in a sample. In many cases,

qualitative analysis will also involve the separation of ions or compounds in a

mixture. Examples of qualitative tests would include ion precipitation reactions

(solubility tests) or chemical reactivity tests. The separation of ions is easily

achieved by taking advantage of their solubility properties. The most common

cations have been placed into five groups based upon solubility in aqueous

solutions when different reagents are added. The reactions which occur are

useful in identifying the presence of these cations in unknown samples. The

process of identifying the cations is called qualitative analysis.

M


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Keep your work-table clean and neat which helps one to achieve the work

quickly in the laboratory.

Record your observations, write down the readings when you make them.

Wash all glass apparatus using dilute solution of detergent.

Wash immediately the apparatus after use.

Do not turn the test tube while heating towards your neighbors.

Turn off gas both tap and water tap whenever they are not in use.

Do not attempt to perform unprescribed experiments unless specific

permission is granted by the teacher in the laboratory.

In the case of any accident like swallowing of chemicals, solutions or

splashing of acids and other chemicals in the eyes or on the body, report

to the teacher immediately.

Wash your hands thoroughly with soap before leaving the lab. If the

soap is not set out in the lab, ask your instructor for it. This hand washing

should be a normal routine at the end of each laboratory period.

General Instructions to the Students


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ToolsFunnel

Test tube

Beaker

Filter papers

Folding filter paper

Rack of test tubes

Conical flask andbeaker


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To prepare for the experiments, you should:

Read the experiment you will be doing.

Covering the specific analytical group you will be working with.

Make marginal notes or high-light directions which you are required to

follow. Note any specific solution preparation directions.

Study the direction for centrifuging, connected with the separation.

Study the flow chart for the analysis and understand the logic in the

chart.

BEFORE COMING TO LABORATORY


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I. Techniques

Addition of reagents

Always use a dropper or capillary pipette when adding a small quantity of a liquid to a test

tube or other vessel. One ml is about 20 drops. If a reagent bottle has a dropper, replace it

promptly after use. Do not allow the dropper to touch the container or solution to which you

are adding the droppers contents. Do not set the dropper down on the bench top or anothersurface, and be sure to return it to the right bottle. Always mix thoroughly after adding

reagent.

Precipitation

To detect the formation of a precipitate on mixing two solutions, it is essential that

both solutions be initially clear; if necessary, centrifuge to clarify. A clear solution

is transparent but not necessarily colorless.After adding a reagent to bring aboutprecipitation, always test for complete precipitation if the purpose is to separate one

substance from another. Suppose, for example, that a solution contains 0.10 millimole of

Ba+2. We add to this solution a few drops of dilute H2SO4, and the amount happens

to contain 0.08 millimole of SO4-2. We have thus produced 0.08 millimole of solid BaSO4,

but 0.02 millimole of Ba+2 remains in the supernatant liquid, because we did not add

enough H2SO4to precipitate all the Ba+2as BaSO4. This fact can be discovered by centrifuging

and adding another drop of reagent (dilute H2SO4in this case) to the clear supernatant. If

precipitation is complete, no additional precipitate will form. However, if insufficient reagent

was added the first time, the additional drop will cause formation of more precipitate. If more

precipitate is observed, add several more drops of reagent, centrifuge, and again test for

completeness of precipitation. Repeat until no precipitate is formed on adding reagent. After

the precipitate and supernatant are separated, the precipitate is washed by adding a few drops

of the washing reagent (usually water), mixing thoroughly with a stirring rod, centrifuging,

and removing the washings with a capillary pipette. Two or more washings are generally

necessary to prevent contamination of the precipitate. Failure to wash precipitates is one

of the most common sources of error in qualitative analysis.

EXPERIMENTAL PROCEDURE


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Transfer of Precipitates

The easiest way to transfer a residue from one container to another is to mix the residue

with small amounts of washing liquid and pour the suspension quickly into the new

container. Repeat this two or three times to get complete transfer. For small volumes,draw the suspension into a pipette for transfer.

Heating of solutions

To avoid excessive evaporation use a water bath. Always stir when heating test tubes. A

water bath with an aluminum test tube holder will be set up for you in your fume hood. Place

your test tubes into the pre-labeled positions and heat the water to a gentle boil.

Adjusting acidity

Always stir well when adding acid or base. To test the pH of the solution, apply a drop onto

litmus paper. Never dip the paper into the solution.

II. Available Equipment

Centrifuge

The centrifuge is used to speed up the separation of a precipitate from a liquid. When a

mixture of solid and liquid is placed in a tube and rotated at high speed in a centrifuge, the

more dense precipitate is forced to the bottom of the tube by a centrifugal force that is many

times greater than the force of gravity. After centrifuging, the supernatant, or clear liquid

above the precipitate, can easily be poured off or withdrawn with a capillary (Pasteur)

pipette. The centrifuge may be damaged if allowed to run unbalanced. Insert your test tubes

in opposite positions in the centrifuge, noting their locations by number. Set the

machine in motion for one minute, which should be sufficient to achieve effective separationof the solid from the liquid. Allow the centrifuge to stop spinning before trying to remove

your test tubes.

Vortex Mixer

This motorized mixer can be used to ensure complete homogeneity after reagent addition.

Simply place your test tube in the cup at the top and gently but firmly press down to achieve

mixing.


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To prepare the salt solution firstly dissolve the solid mixture in the proper

solvent by trying the following solvents in the cited order.

1 Distilled water (Cold and then hot).

2 Dilute hydrochloric acid (HCl) (Coldand then hot).

3 Dilute nitric acid (HNO3) (Coldand then hot).

4 Conc. hydrochloric acid (HCl) (Coldand then hot).

5 Conc. nitric acid (HNO3) (Coldand then hot).

6 Aqua regia [Conc. HCl + Conc. HNO3 3 : 1 ( v/v)]

Notes:

If the solid mixture is soluble in a certain solvent on hot and reprecipitate

on cooling in this case dissolve in the next solvent.

It is better to prepare the solution as concentrated as possible. The obtained

solution must be clear regardless of its colour.

Preparation of the salt solution


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Classification of cations

Group Group reagent Cations Distinguishing features

I

(Silver group) Dilute HCl Ag+, Pb

++, Hg2

++

Precipitate as

Chlorides

II(Acid sulphide group) HCl + H2S

Hg

++

, Pb

++

, Bi

+++

, Cu

++

, Cd

++

,Sn

++, As

+++, Sb

+++, Sn

++++

Precipitate asSulphidesin acid medium

III

(Iron group) NH4OH + NH4ClAl

+++, Cr

+++, Fe

+++ Precipitate as

Hydroxides

IV

(Alkaline sulphide

group)

NH4OH + NH4Cl+H2S

Ni++

, CO++

, Mn++

, Zn++

Precipitate as

Sulphidesin alkaline medium

V

(Alkaline earth

group)

NH4OH + NH4Cl +(NH4)2CO3

Ba++

, Sr++

, Ca++

Precipitate as

Carbonates.

VI

(Alkali metal group)

No

group reagent

Mg++

, Na+, K

+, NH4

+ Ions not Precipitate in previous

groups.

Note: The ions indicated with a Roman numeral probably do not exist as simple ions in solution and the Roman numeral given is the oxidation

state.


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Silver (Ag+), Lead (Pb

++), and Mercurous(Hg2

++)

This group is insoluble in water,

Group reagent is cold dilute hydrochloric acid (HCl).

Group (I) is precipitate as chloride.

Chemistry of Group (I)

The more commonly encountered cations can be separated and analyzed

according to the solubilites of their various compounds in water, acid, etc. The cations

in analytical group (I) are silver ion, mercury or mercurous ion, and lead ion. The

chlorides of these cations are practically insoluble in cold dilute hydrochloric acid,

and these are the only common chlorides which are insoluble. This insolubility may

be used to effect the separation of this group of cations from other cations which

might be present but which do not form insoluble chloride salts.

In the first step,

If a dilute solution of HCl is added to a solution containing ALLof the common metal

ions, a white precipitate will be formed. This precipitate will contain AgCl(s),

Hg2Cl2(s), and PbCl2(s). If this solution is centrifuged to collect the solid material at

the bottom of a test tube, the supernatant liquid can be removed (decanted). The

remaining solid can be washed with distilled water so that the ONLYmetal ions that

remain are Ag+, Hg22+, and Pb2+. The reactions that occur are

Ag+

(aq)+ Cl-(aq)-> AgCl (s)

Hg22+

(aq)+ 2 Cl-

(aq)-> Hg2Cl2 (s)

Pb2+(aq)+ 2 Cl- (aq)-> PbCl2 (s)


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The reactions are conducted in acidic solution, to avoid the possibility that

these and other metal ions might be precipitated as hydroxides or oxides. This

reaction of this group of ions with chloride ions allows them to be separated from allother metal ions. Silver, mercurous, and plumbousions have been designated as the

Group I Cations.

If addition of dilute HCl to a solution of metal cations results in a precipitate, this is

conclusive evidence that at least one - and possibly all - of the Group I Cationswereare present in the original solution. Additional tests are necessary to determine which

of these three cations are present in the precipitate.

While these three chlorides are relatively insoluble in cold water, lead chloride

is found to be quite soluble in hot water. Therefore, cold water may be added to theprecipitate containing any or all of the three chlorides without any of them re-

dissolving. However, heating this mixture will cause lead chloride to dissolve, if anyis present. While still hot, the tube can be centrifuged and the supernatant solution

can be decanted into another test tube. If any lead ion is present, addition of cold HCl

solution to the liquid will cause white lead chloride to precipitate.

Silverion has a special property which distinguishes it from the other two cationsof Group I. When mixed with ammoniain basic solution, complex ions are formed

(these complexes are not formed in acidic solution in which the ammonia exists asammonium ion):

Ag+ (aq) + NH3 (aq) = Ag(NH3)+ (aq)

Ag(NH3)+

(aq) + NH3(aq) = Ag(NH3)2+(aq)

The formation of these complex ions lowers the concentration of free silver ion,allowing precipitated silver chloride to dissolve:

AgCl(s) + x NH3(aq) -> Ag(NH3)x+(aq) + Cl

-(aq) ; x = 1 to 2 .

Thus, when the Group I cations are precipitated with HCl, ammonia may be added to

the precipitate until litmus indicate that the solution is basic. If the precipitate ontainssilver ion, it will dissolve and may be removed from the others by centrifuging and

decanting the supernatant solution. Addition of HCl to this solution until litmusindicates that the solution is acidic will re-precipitate silver ion, if present.Mercurouschloride may be distinguished from the other two Group I chlorides by its ability to

resist re-dissolving by either heating or the addition of ammonia.


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Silver (Ag+), Lead (Pb++), and Mercurous(Hg2++)

1- Take 1ml of the mixture + 1ml of cold dilute HCl if white precipitate(ppt.) is

formed that means group (I)is present. The filtrate contains other groups.

2-

Then transfer the ppt. into a clean beaker; add water, boil, and then filter.

FiltrateContains PbCl2

PrecipitateContains AgCl and Hg2Cl2

Pour hot ammonium hydroxide solution on the ppt. and collect

the filtrate.Filtrate Precipitate

Confirmation of

lead(Pb2+

)

Take portion of filtrate +

acetic acid (CH3COOH) +

potassium dichromate

Yellow ppt. (PbCrO4)

Confirmation of silver

(Ag+)

Take portion of filtrate + dilute

nitric acid (HNO3)

White ppt. (AgCl)

Confirmation of

mercuros (Hg22+

)

The ppt.

(Hg0+ Hg (NH2) Cl)

is dissolve in aqua regia, then

heat to evaporate excess aqua

regia., add SnCl2.

White ppt.

Turns to gray


potassium iodide solution.

Yellow ppt. (PbI2)

Soluble by boiling


solution of potassium iodide

Pale yellow ppt. (Agl)Take portion of filtrate +

dilute sulphuric acid.

White ppt. (PbSO4)Soluble by boiling in amm.

acetate solution.

L e a d

is present

S i l v e r

is present

M e r c u r o u s

is present

Group (I)


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EXPERIMENT 1: Qualitative analysis results of group (I)

Report sheet

Physical properties

Colour : .. Shape : .

Solubility : ..

Chemical properties

Experiment Observation Results


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Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties


Conclusion


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Group (IIA): Lead (Pb2+

), Mercuric (Hg2+

), Bismuth (Bi3+

), Copper (Cu2+

),

and Cadmium (Cd2+

)

Group (IIB): Arsenic (As3+,5+

), Antimony (Sb3+,5+

) and Stannate (Sn2+,4+

)

It is called the Acid Sulphide group

Group reagent : dil HCl + H2S

Both group II and group IV have their sulphides insoluble in water. But

group IV has higher Ksp (needs high S-2

to precipitate).

So to precipitate the group IIonly we use dilute HCl with H2S

Chemistry of Group (II)

The next two steps in the flow chart separate group II ions and group III ions from the

remaining solution by their ability to form insoluble sulfides upon reaction with H2S.

M2++ H2S MS(s) + 2H+

This equilibrium is really a combination of three standard equilibria:

H2S HS- + H+ Ka1= 8.910

-8

HS S2- + H+ Ka2= 1.210-13

M2++ S2- MS(s) 1/Ksp

When these are combined (added together), the resulting equilibrium constant is strongly

dependent on the Kspof the particular sulfide (MS). According to the common ion effect rule,

addition of strong acids will shift equilibrium to the left, leading to a sharp decrease in [S -2] in

the solution. On the other hand, alkaline medium enhances ionizations of H2S producing higher

concentration of sulphide ion in solution. Group (IV) sulphides having higher solubility products

than those of group (II) may precipitate if the acidity of the solution is lower than 0.2N. If theacidity is higher than 0.3N sulphides of lead, candmium and tin are not completely precipitated.


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1. To the filtrate from group (I), add dilute HCl + H2S gas. If precipitate is formed.

2. Group II is present

3. Filter, and then dilute the filtrate with HCl, add excess H2S till no ppt.

FiltrateContains groups 3, 4, 5 and 6

PrecipitateContains sulphides of group 2A and 2B

Step 1

Separation of group (IIA) from group (IIB)

1-Transfer ppt. of group IIAand IIBinto a clean beaker, add ammonium sulphide, heat with

stirring and then filter.

FiltrateContains group (IIB)

PrecipitateContains group (IIA)

AS2S5 Ammoium thio-

arsenate

Yellow

ppt.

HgS Mercuric sulphide Black

ppt.

Sb2S5 Ammonium thio-

antimonate

Orange

ppt.

CuS Copper sulphide Black

ppt.SnS2 Ammonium thio-

stannate

Yellow

ppt.

Bi2S3 Bismuth sulphide Dark

brown

CdS Cadmium sulphide Cannary

yellow

Step 2

2- Transfer the precipitate of group IIA into a clean beaker, add dilute nitric acid (HNO3), boil,

and then filter.

Precipitate Filtrate

Contains mercuric sulphide

(HgS)

Note

May be yellowish is formeddue to sulphur.

Dissolve in aqua regia, heattill the excess of sulphur,

dilute with water, and add

solution of SnCl2 white ppt.changes to grey.

Contains nitrate of Bi, Cu, Cd, and Pb

Take portion of filtrate + H2SO4if white ppt. is formedthat means lead is present.

Here, precipitate all of Pb in the filtrate using conc.H2SO4 and boil, cool, dilute with water, filter and

neglect the ppt.

Add to the filtrate excess NH4OH.

If whit ppt. is formed bismuth also is present.

Group IIA


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Mercuric is present Hg2+


Contains Bi(OH)3

Confirmation of Bismuth

(Bi+3):-

Dissolve in least amount of

dilute HCl then add sodium

stannite solution.

if black ppt. is formed

Bismuth Bi3+

Note:Preparation of sodium

stannite solution:

SnCl2 solution + NaOH

white ppt. and then add

excess NaOH.

Contains copper (Cu+) and

cadmium (Cd2+)

Detect in presence of each

other

Detection of copper:1-

Blue colour indicate

copper

2-

Portion + acetic acid +

potassium ferrocyanide

k4[Fe(CN)6].

If brown ppt. is formed

Copper Cu2+

is present

Detection of copper in

presence of copper:1-

Take portion + KCN till

the solution became

colourless add H2S.

If yellow ppt. is formed

Cadmium Cd2+

is present

2- If copper absent, add H2S

directly


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EXPERIMENT 2: Qualitative analysis results of group (IIA)

Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties


Conclusion


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Aresnate (As3+,5

)+, Antimonate (Sb

3+,5)

+,and Stannate: (Sn

2+,4+)

1-

Transfer the precipitate of group IIBinto a beaker.

2- Add solid ammonium carbonate + some water, boil, and then filter.

Filtrate Precipitate

Filtrate contains:Aresnate (AS3+) as Ammonium

thioarsenate

Take portion of filtrate + conc.

HCl

Yellow ppt.

Arsenic is present

Precipitate contains:

Ammonium thio-antimonate Sb2S3(orange)Ammonium thio-stannate: SnS (yellow)

. . ,

Then divided the solution into two portions:

Test for Tin:Take portion of solution add iron powder, heat, filter and

then add HgCl2

White ppt.(turns to grey or black)

Test for Antimony in presence of Tin:Take portion of solution add NH4OH + solid oxalic acid,

heat, and then add H2S.

If orange precipitate is formed

Antimony is present

Test for Antimony in absence of Tin:Take portion of solution+ H2S if orange precipitate is

formed.

Antimony is present

Group (II)B


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EXPERIMENT 3: Qualitative analysis results of group IIB

Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties


Conclusion


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Ferric (Fe3)+, Aluminum (Al

3+), and Chromium (Cr

3+)

It is called Ammonium hydroxide

Group (III)is precipitate as hydroxide

Group reagent: NH4Cl + NH4OH


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Ferric (Fe3)+, Aluminum (Al3+), and Chromium (Cr3+)

1- To the filtrate from group IIadd conc. HNO3, boil for 3 minutes, add excess NH4CL,

boil again and then add NH4OH. If precipitate is formed.

2- Group (III) is present.


Contains: Contains:

Groups 4, 5, and 6

Aluminum

hydroxide

Al(OH)3 Whit gelatinous ppt.

Chromium

hydroxide

Cr(OH)3 Green ppt.

Ferric hydroxide Fe(OH)3 Reddish brown ppt.

3- Transfer the precipitate into a clean beaker, add excess NaOH, boil, and then filter.


Contains:Sodium aluminate

Confirmatory test:

Take portion of filtrate + solid

NH4Cl boil till no odour of

ammonia

If white precipitate is formed

Aluminum

is present

Contains: Cr(OH)3 and Fe(OH)3

ppt. + (Na2O2+H2O), strong boil, and then filter


If yellow in colour

K2CrO4present

Confirmatory test:Take portion of filtrate +

acetic acid + lead acetate

Yellow ppt.

Chromium is present

If brown ppt. in colour

Fe(OH)3 present

Confirmatory test:Take portion of ppt. +

K4[Fe(CN)6]

Prussian blue

Take portion of ppt. + NH4CNS

Blood red

Iron is present

Group (III)


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EXPERIMENT 4: Qualitative analysis results of group III

Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties


Conclusion


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Manganese (Mn2+

), Zinc (Zn2+

), Cobalt (Co2+

), and Nickel (Ni2+

)

This group is called Ammonium sulphide group

Group reagent: NH4Cl + NH4OH + H2S

Group IV is precipitateas sulphide in alkaline medium


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Manganese (Mn2+

), Zinc (Zn2+

), Cobalt (Co2+

), and Nickel (Ni2+

)

1- To the filtrate of group III, add NH4Cl (solid) + NH4OH solution, and add H2S till complete

precipitation. If precipitate is formed.

2- Group IVis present.


Contains:

Group V& VIContains:

CoS

NiS

MnS

ZnS

Cobalt sulphides

Nickel sulphides

Manganese

sulphides

Zinc sulphides

Black ppt.

Black ppt.

Buff ppt.

White ppt.

3- Transfer the ppt. into a clean beaker add dilute HCl , stir , wait for 3 minutes , and then

filter the solution.


Contains : CoS + NiS Black

Dissolve the precipitate in aqua regia ,

evaporate till nearly dryness, dilute with

water , divide into 3 portions.

Test for Ni:Take a portion of precipitate + NH4OH +

Dimethylglyoxime

Red PPt.

Ni2+

is present

Test of Cobalt:Take a portion of precipitate + NH4CNS

Blue colour

Pot. Cobaltnitrite test :

Take a portion of precipitate + KNO2+

acetic acid Yellow PPt

Co2+

is present

Contains: MnCl2+ ZnCl2Boil the filtrate to expel H2S , add Excess NaOH ,

Boil , Filter


Contains: Mn(OH)2

Dissolve the ppt. in

conc.HNO3 , add

lead oxide

(PbO),boil for 3

minutes, and wait,

violet color

Mn2+

is present

Contains: NaZnO2

Take a portion of filtrate+ H2S gas

White ppt.

ZnS.

Take a portion of filtrate +Acetic acid + K4[Fe(CN)6]

white ppt. of Zn2[Fe(CN)6],

may be yellowish white

Zn2+

is present

Group (IV)


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EXPERIMENT 5: Qualitative analysis results of group IV

Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties


Conclusion


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Barium (Ba2)+, Strontium (Sr2+) , and Calcium (Ca2+)

It is called Alkaline earth group or Ammonium carbonate group

Group reagent : NH4Cl + NH4OH + (NH4)2CO3

The cations precipitate as carbonate in alkaline medium


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Barium (Ba2)+, Strontium (Sr2)+, and Calcium (Ca2+)

1. To the filtrate of Group IV add NH4Cl till alkaline, heat, and then add ammonium

carbonate (NH4)2CO3 white ppt. then Group V is present.


Contains :Group VI

Contains:CaCO3

BaCO3

SrCO3

Calcium carbonate

Barium carbonate

Strontium carbonate

White ppt.

White ppt.

White ppt.

2. Transfer the precipitate into the beaker, add acetic acid till dissolve, and boil.

3. To a portion of this solution add K2CrO4 (potassium chromate) if yellow ppt.

then add K2CrO4to the whole solution, and filter.


Contains :BaCrO4

Dissolve in conc. HCl, evaporate till

dryness,

Use the residue in flame test Applegreen.

Ba2+

is present

Contains: SrO4& CaCrO4

Take portion of the ppt.+ conc soln. of CaSO4 White

ppt.

Sr2+is present

In this case add CaSO4to all the solution, boil , and then

filter


Contains :SrSO4Dissolve in conc.HCl

,evaporate till dryness, use

the residue in flame test

Crimson red

Sr2+

is present.

Contains: complex of

calcium ammonium

sulphate.

Portion + amm. oxalate

White PPt.Evaporate portion till

dryness and use the residue

in

Flame test Brick red

Ca2+

is present.

Group (V)


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EXPERIMENT 6: Qualitative analysis results of group (V)

Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties


Conclusion


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Magnesium (Mg2+

), Sodium (Na+), Potassium (K

+), and (NH4

+)

This group is known as

Alkali metal group


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Magnesium (Mg2+

), Sodium (Na+

), Potassium (K+

), and (NH4+

)

Test of magnesium Mg+ Test of potassium K

+& Sodium Na

+

Portion of filtrate of group V + NH4Cl

(solid) + NH4OH + excess of sodium

phosphate shake strong White PPt.

Mg2+

is present.

MgSO4+ Na2CO3 Na2SO4+ MgCO3

(White)

MgSO4+ 2 NaOH Na2SO4+ Mg(OH)2

(White)

Evaporate large portion of filtrate till no white

fumes of ammonium salts then add conc. HNO3,

add water to dissolve any formed precipitate. And

then divide the solution into two portions:

1- Test for potassium K+

Cobalt nitrate solution + amount of NaNO2

+ drops of acetic acid then add this

solution to a portion of the solution if

yellow ppt.

Potassium K+is present

2-

Test for sodium Na

+

Flame test Golden

yellow colour

Sodium Na+is present.

Group (VI)


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EXPERIMENT 7: Qualitative analysis results of group (VI)

Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties



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Report sheet

Physical properties


Solubility : ..

Chemical properties


Conclusion


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Test for Ammonium

To test for ammonium ions (NH4+), sodium hydroxide solution is added to the test

solution and gently heated. If ammonium ions are present, ammonia gas will be

given off. This can be shown in the following equation:

Ammonium ions + hydroxide ions ammonia + water

NH4+

(aq)+ OH-(aq)==> NH3(g)+ H2O(l)

The hydroxide ion removes a proton from the ammonium ion to release the

ammonia

Observation

Smelly ammonia releasedand red litmus turns blue, gentle warming helps BUT

the ammonia should be released at room temperature.

Ammonia gas is evolved because alkali frees ammoniafrom its salts.


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EXPERIMENT 8:

Report sheet

Physical properties


Solubility : ..

Chemical properties


Conclusion


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Scheme For Identification of Basic Radical in Mixture

Solution Containing one or more of the members of each group

Cold dil. HCl

ppt.Filtrate

[dil HCl +H2S]

Filtrateppt.

Chlorides of group I Follow analysis as

represented by the scheme of group I

Containing soluble Cations of

group II.III, IV, V and VI

Sulphides of group II Follow

analysis as represented by the

scheme of group II

Containing soluble Cations

of group III, IV, V and VI

To filtrate of group II add concentrated HNO3 . Boil for 3 minutes to make

1-Oxidation of ferrous to ferric 2- Oxidation of H2S gas to S.


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To Filtrate of group II add

NH4Cl +NH

4OH

ppt.. Filtrate

Filtrate

ppt.

Hydroxides of group III Follow analysis

as represented by the scheme of groupIII


group IV, V and VI

Carbonates of group V Follow


scheme of group V

Containing soluble Cations

of group V and VI

NH4Cl +NH

4OH +H2S

Sulphides of group IV Follow


scheme of group IV


group VI. Follow analysis From

scheme VI

NH4Cl +NH

4OH till alkaline b0il + (NH

4)2CO

3

ppt..

Filtrate


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General questions

Why slight excess of hydrochloric acid is added to group (I)?.

We add slight excess HCl to ensure complete precipitate of group (I), by the common ion

effect.

Why dil. HCl is added to group (I)?.

Because PbCl2 tends to form soluble complex and escape to group II in conc. HCl (i.e

PbCl2is soluble in excess Cl-)

Pb+2+ Cl- PbCl2

PbCl2+ Cl-

[PbCl3]-

+ Cl-

[PbCl4]2-

Soluble complex

Why not use conc. HCl to ensure that group IV will not interfere?

Because if we use conc HCl the concentration of S2-ion will decrease dramatically that it

becomes insufficient to ppt. some cations of group II which has slightly high Ksp eg: Cd,

Pb, Sn..

Therefore we have to adjust acidity. The suitable acidity was found to be 0.2 - 0.3 N HCl

(0.25N). We use crystal violet (external indicator) to adjust acidity.

Why do we oxidize Fe2+

to Fe3+

?

Because H2S used in pptn of group II is a reducing agent which reduces Fe+3(if present)

to Fe+2 and Fe(OH)2has high Ksp so not ppt. in conditions such that of group III but

Fe(OH)3has a lower Ksp which can ppt with group III and iron does not escape

Why do we boil after NH4Cl ?

1- To coagulate the ppt.

2- To break Cr Amine complex

[Cr(NH3)6] (OH)3 Cr(OH)3+ 6NH3

soluble Cr amine complex


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3- To expel O2and prevent oxidation of manganus (Mn2+) which has higher Ksp i.e. [not

ppt. as OH-] to (Mn3+) which has low Ksp and can be ppt. as Mn(OH)3so it escapes

from group IV to group III

Why do we add NH4Cl ?

By common ion effect it decreases OH-conc. so prevent pptn of group IV as hydroxide

Before we test for K+we must remove NH4+.

Because NH4+gives all tests for K+

Write the color of the precipitate formed

PbCl2+ K2CrO4 PbCrO4+ 2 KCl ..ppt

[Ag(NH3)2]Cl + 2 HNO3 AgCl + NH4NO3 ..ppt

Hg2Cl2+ excess SnCl22 Hg + SnCl4 ..ppt

Cu ++ [Fe(CN)6]4 Cu2[Fe(CN)6] ..ppt

(Cu(NH3)4] ++ 2 CN Cu(CN)2 ..ppt

[Cd(CN)4]-+ H2S CdS + HCN + CN ..ppt

Fe ++ K4[Fe(CN)6] K Fe [Fe(CN)6] ..ppt

CrO -+ H2O2 CrO4- + 4 H2O ..ppt

Pb(CH3COO)2+ (CrO4)- PbCrO4 ..ppt

Al(OH)3+ OH

-

AlO

-

+ H2O ..ppt

Zn ++ [Fe(CN)6]- Zn2[Fe(CN)6] ..ppt

MgSO4 + 2NaOH Na2SO4+ Mg(OH)2 ..ppt

K+ ion give .. color in Flame test


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cations separation exp

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