CHM 474 exp 1

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CHM 474

INORGANIC CHEMISTRY

EXPERIMENT 1 & 2 :

QUALITATIVE ANALYSIS FOR

IDENTIFICATION OF METAL CATION AND

TRANSITION METAL

NAME : NUR SYAFIQAH BT CHE KAMARUDIN GROUP : AS2022M2

LAB PARTNER : AMIRAH FARZANA BT AZMAN

LECTURER’S NAME : DR. AMALINA BT MOHD TAJUDDIN DATE OF EXPERIMENT : 17 MAC 2016

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1. To perform qualitative analysis to identify the cations

2. To study the solubility and reactivity of each of metal cations. 3. To verify the ions presents by process of separation method.

INTRODUCTION :

In order to verify and detect the presence of specific ions especially in aqueous solutions, we know that it is measured by qualitative analysis, where qualitative analysis is a process in which the components of the mixtures are separated and can be identified as it is confirm any presence or absence of certain substances. A basic of qualitative analysis is by knowing what are the component that present in each of different samples as some samples that contains the ions will have to undergoes a specific chemical reaction with certain reagent that can be used to yield the observable product. Furthermore, qualitative selection of ion are commonly accomplished by a system analysis where the precipitation act as a role in order to know what actually the ions present.

Different solubilities causing the ion to be separated in solution. Commonly, a metal ion in mixture can form a kind of solid for that is precipitate in the presence of specific anions , while some of it will dissolved. Then two ions are separated by process of centrifuge to separate the precipitate form in solution. the clear solution called as the supernatant was decanted or poured into another test tube and being used for the next stage. The solid formed was left behind as it is to show that both solid indicate insoluble solution and liquid solution as soluble solution are completely separated.

For example, the reaction between Group I cations include Ag+_{, Pb}2+ _{and Hg}2+ _{formed the precipitate} when it is reacted with the hydrochloric acid, HCl. The precipitate formed indicating that it produce the insoluble chloride salt. Other examples is when group II cations such as As2+_{. Bi}3+_{, Cd}3+_{. Cu}2+ Hg2+_Pb2+_Sn4+_{react with acidic hydrogen sulphide, there is precipitate are formed because these ions} are insoluble in sulphate salts.

APPARATUS AND EQUIPMENT:

Test tubes, test tube holder, test tube rack, centrifuge machine, Thermometer, hot water bath, glassrod, Unknown Solution I, Unknown Solution II, mixture solution, dH2O, 1M thioacetamide, NH3 , 6M HCl, 1M K2Cr2O4

PROCEDURES : Experiment 1 Procedure A.

1. 2 drops of 6M HCl was added to 1 mL of unknown I, unknown II and the mixture of the cation.

2. If ppt chloride formed, the suspensions was centrifuged for a minute.

3. 1 additional of 6M HCl was added to clear supernatant to check for complete precipitation. 4. If ppt observed, the suspension was centrifuged again.

5. The supernatant was decanted to another tube. 6. The supernatant was saved for procedure B.

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For experiment 2 , if it is precipitate, the precipitate was washed and 10 drops of 6M NH3 was stir to dissolve. The 6M NHO3 was added dropwise. Then the solution was discarded and is continued for the procedure B.

Procedure B

1. 6M of NH3 was added to the solution until it is basic.

2. The sample was placed in a boiling water bath for 2-3 minutes to remove excess NH3. 3. The volume solution was adjusted to 2ml with distilled warer and 10 drops of 6M HCl was

added.

4. 12 drops of thioacetamide was added to solution and was stirred.

5. The sample in the boiling water was heated for 10 minutes to allow for the hydrolysis of thioacetamide producing H2S.

6. If ppt formed, the sample was centrifuged for 2 minutes and the supernatant was decant to another clear test tube and saved for procedure C.

For experiment 2, if ppt was formed, the precipitate was washed and being centrifuge. Then the precipitate was saved and the supernatant was discarded. Then, 20 drops of 6M HNO3 was added into solution and was boiled for several minutes with stirring occasionally. After centrifuged, 6M NH3 was added until acidic and 10 drops of 0.1 M K4Fe(CN)6 was added and stirred. Then the solution was tested and proceed for procedure C.

Procedure C

1. 3 additional drop of 1M thioacetamide was added to supernatant and being reheated for 5 minutes.

2. If ppt formed, the sample was centrifuged and the supernatant was decanted to clear tube. 3. The volume of solution was adjusted to 3ml with distilled wate and 10 drops of 6M HCl

was added.

4. 6M NH3 was added dropwise until solution basic.

5. 5 additional drops of NH3 was added and 12 drops thioacetamide and the mixture was stirred thoroughly.

6. The sample was heated in boiling water bath for 10minutes.

7. If ppt formed, the sample was centrifuged and the supernatant was decanted and was saved for procedure D.

For experiment 2, if ppt was formed after procedure c, the precipitate was washed and 6M NH3 was added and being centrifuged again. Then, the precipitate solution was added with 20 drops of 6M HNO3 and being heated in a boiling water bath fr several minutes while stirring. The solution was centrifuged and the precipitare was discarded and supernatant was obtained for conformation test.

Procedure D

1. 6M NH3 was added dropwise to the sample until basic. 2. 10-15 drops of NH3 was added to the buffer solution.

3. 20-30 drops of (NH4)2CO3 was added to sample and was stirred.

4. The test tube containing ppt of carbonate was transferred a warm water bath of 70-80oC for 2-3 minutes.

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5. After sample have been warmed, the mixture was centrifuge and the supernatant was decanted containing either Na+ _{and K}+

6. The ppt was saved from procedure D(i).

Procedure D(i)

1. The ppt was washed with 2 ml of distilled water, and being centrifuged and was decanted.

2. 6M of acetic acid was added dropwise and stirred to dissolved ppt. 3. A few drops of acetic acid was added more until it was acidic. 4. 6 drops of 1M K2CrO4 was added to solution and stirred. 5. If ppt formed, centrifuged.

6. The supernatant was saved for procedure D(ii).

Procedure D(ii)

1. 10 drops of K2CrO4 was added to the solution and being stirred for 10 minutes. 2. If ppt oxalate formed, centrifuged.

Experiment 2 was continued from procedure C. 10 drops of 6M NH3 was added until basic and 6M CH3COOH was added too until it is acidic. Then, 10 drops of 0.1 M K4Fe(CN)6 was added and was mixed thoroughly. The precipitate formed and was centrifuged.

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Experiment 1

1. on adding HCl to the initial sample

OBSERVATION BALANCED CHEMICAL

EQUATION

UNKNOWN I Cloudy with white precipitate Ag+ _{+ Cl}- _{ AgCl}

UNKNOWN II Clear solution with no precipitate

-MIXTURES Blue solution with white Precipitate Ag+ _{+ Cl}- _{ AgCl}

2. On adding H2S under acidic condition

EQUATION

UNKNOWN I No precipitate

-UNKNOWN II Black precipitate Cu2+ _{+ S}2- _{ CuS}

MIXTURES Black precipitate with cloudy solution Cu2+ _{+ S}2- _{ CuS}

3. On adding H2S under basic condtions.

EQUATION

UNKNOWN I Greyish precipitate Zn2+ _{+ OH}- _{ Zn(OH)2}

UNKNOWN II White precipitate Zn2+ _{+ S}2- _{ ZnS}

MIXTURES Grey precipitate with black solution Zn2+ _{+ S}2- _{ ZnS}

4. On adding CO3

2-OBSERVATION BALANCED CHEMICAL

EQUATION

UNKNOWN I Clear solution with no precipitate

-UNKNOWN II White precipitate with cloudy solution Ba2+ _{+ CO3}2-_{ BaCO3}

MIXTURES Clear solution

-5. On adding CrO4

2-OBSERVATION BALANCED CHEMICAL

EQUATION

UNKNOWN I Clear solution without precipitate

-UNKNOWN II White precipitate with cloudy solution Ba2+ _{+ CrO4}2- _{ BaCrO4}

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OBSERVATION BALANCED CHEMICAL EQUATION

UNKNOWN I Clear solution

-UNKNOWN II No precipitate Mg2+ _{+ C2O4}2- _{ MgC2O4}

-Unknown Number I contains Ag + _Cu2+ _Zn2+

Unknown Number II contains Cu 2+ _Zn2+ _Ba2+ _Mg2+

Mixture contains Ag 2+ _Cu2+ _Zn2+

Experiment 2

1. On adding HCl to the intial sample.

EQUATION

KNOWN White precipitate Ag+ _{+ Cl}- _{ AgCl}

UNKNOWN Clear solution

-Confirmatory test for cation.

EQUATION

KNOWN Cloudy with white precipitate Ag + Cl- _{ AgCl}

UNKNOWN Clear solution

2. On adding H2S under acidic condition.

EQUATION

KNOWN Cloudy with white precipitate Ag+ _{+ Cl}-_{ AgCl}

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OBSERVATION BALANCED CHEMICAL EQUATION

KNOWN Dark brown solution with black

precipitate

2Cu2+ _{+ Fe(CN)6}4- _ Cu2{Fe(CN)6]

-3. On adding H2S under basic condition.

EQUATION

KNOWN Black precipitate Zn2+ _{+ S}2- _{ ZnS}

UNKNOWN Cloudy precipitate with white

precipitate

Zn2+ _{+ S}2- _{ ZnS}

Confirmatory test for the cation.

EQUATION

KNOWN Light green solution with

precipitate

3Zn2+ _{+ 2Fe(CN)6}4- _ Zn[Fe(CN)6]2

UNKNOWN Light green solution with

precipitate

3Zn2+ _{+ 2Fe(CN)6}4- _ Zn[Fe(CN)6]2

Known solution contain Zn _{, Ag}2+ + _,Cu2+

Unknown solution contain Zn 2+

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In order to determine and identify the metal ions in the solution by performing qualitative analysis, several of tests and method have been conducted. For experiment 1, theoretically there are five groups of metal cations that we can determine through its chemical and physical changes and behaviour. Firstly, when the sample of Unknown I, Unknown II and Mixture react with the HCl, the result shows that there is precipitate formed in Unknown I and Mixture. Based on observation, the two samples contain ions that are insoluble salt of chloride due to formation of white precipitate in Unknown I and blue precipitate in Mixture II shows that the ions presented can be silver ion, Ag+, Mercury ion Hg+ and lead ion, Pb2+. Most chloride salt are soluble except for these three, and these salts are hardly distinguished as it gives the white solid precipitate. By then, it is expected that the precipitate formed was silver chloride, AgCl by the chemical equation

Ag+ _{+ Cl}- _{ AgCl}

And this part was obey to the analytical group II cations.

For the analytical group II cations, the sulphide salts was tested with dilute of HCl in order to keep the sulphide ion concentration at a minimum leve, resulting the precipitation was allowed to settle down.When the sample react with thioacetamide forming the hydrogen sulphide under acidic

condition, the result show that Unknown II and mixture have the black precipitate in the solution. the formation of black precipitate was clearly indicated that it was Cu because usually the insoluble sulphide compound are generally black in colour. Suppose in theory we know that suppose the blue precipitate are expect to formed due to presence of ammonia solute, whee the Cu tend to give a blue solution without precipitate. However we that CuS was formed and it is insoluble salt. The chemical equation for this reaction Cu2+ _{+ S}2- _{ CuS . For the basic condition, when the unknown solution and} mixture, the three solution have showed the result of forming the precipitate. Unknown I contain the black precipitate and unknown II formed white precipitate by showing the chemical equation of Zn2+ ₊ OH- _{ Zn(OH)2 that have greyish precipitate. While Zn}2+ _{+ S}2- _{ ZnS for white precipitate and grey} mixture with black precipitate for Zn2+ _{+ S}2- _{ ZnS.}

For carbonate salts, it is in connected to analytical group IV cations which are mostly insoluble in water. Usually it was added with NH4CO3 with a neutral basic or pH. Thereotically, all carbonates are insoluble except the alkali metal and NH4+ _{. since for this part the unknown II reveal precipitate, we} expect that the ions present in this salt was Ba2+ _{from the chemical equation Ba}2+ _{+ CO3}2-_{ BaCO3} forming white precipitate with cloudy solution.

Next, when being added with chromate ion. The unknown solution show the result of white

precipitate with cloudy solution. thus, we indicate the ions presented in sample was Ba2+_{that formed} white precipitate. When actually the real colour of it was yellow in colour with precipitate. And the chemical equation is Ba2+ _{+ CO3}2-_{ BaCO3}

In part 5 of adding dichromate ion, theoretically most of dichromate salt are soluble and some are not. based on the result, unknown solution II give the result where it formed no precipitate showing that it was magnesium dichromate by equation :_

Mg2+ _{+ C2O4}2- _{ MgC2O4 (s)}

For experiment 2, the experiment was conducted continuosly from experiment 1 in order to proceed for the confirmatory test especially for ion of Ag+ _{Cu and Zn that are involving the redissolving the} metal cation followed by receprecipating it. since the precipitate we obtained when adding HCl to the sample in experiment 1, the precipitate was washed with ammonia solution and added with some

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nitric acid for the confirmatory test. the result obtained for this part was a white solid indicate that presence of Ag+ _{are confirmed.}

For the next part when the salt formed with precipitate when added H2S in acidic condition, the unknown sample that formed the grey precipitate with light blue solution that formed was Cu2+ in experiment was tested. The precipitate of CuS salt formed was washed and centrifuge. Then it was added with nitric acid and being boiled by chemical equation Cu2+ _{+ S}2- _{ CuS}

The procedure was continued when ammonia solution was added until and adding more of sulphuric acid and adding Ke4Fe(CN)5 and the precipitate of dark brown solution with precipitate formed in the known solution by this equation of chemical reaction :- 2Cu2+ _{+ Fe(CN)6}4- _{ Cu2{Fe(CN)6] showing} that the presence of Cu2+ _{was confirmed. While for the unknown solution it give a just only clear} solution.

In basic condition, when adding the H2S the known solution give the black precipitate and the unknown solution of cloudy precipitate showing it contain Zn2+ _{ions the sample was tested in order to} verify the Zn2+ _{after added with H2S since the supertant appeared , the supernatant was continued by} adding drops of HCl and NH3 to buffer, there will be precipitate showing that precipitate of Zns. Then, the precipitate was added with HNO3 and being heated. The result for this part of experiment showing the light green solution precipitate for known and unknown solution by equation chemical of 3Zn2+ _{+ 2Fe(CN)6}4- _{ Zn[Fe(CN)6]2 . after ppt formed, the presence of Zn is confirmed. It is show} that the Zn are undissolved in some kind of solution. same goes to othe reactant.

However, during conducting the experiment, there might be some errors and some step of precaution needs to be taken in order to get accurate result and minimizing the error. Firstly the errors of the solution was the time where precipitate are formed but hardly to centrifuge that can affect the other chemical reaction to be occur and maximizing errors. Suppose any precipitate formed should be centrifudge to get the supernatant that might be used for the next experiment. During experiment, the students should wear gloves as the reagent used was a bit corrosive that might give injured to our body. Next, all apparatus that have been used should be rinsed first to remove any unwanted tracers that might give error in the experiment.

CONCLUSION :

In conclusion, for experiment 1, every sample have various kind of ions. Unknown Number I contains Ag+ _Cu2+ _Zn2+_{. Unknown Number II contain Cu}2+ _Zn2+ _Ba2+ _Mg2+ _{and the mixture} contains Ag2+ _Cu2+ _Zn2+ _{. for experiment 2, known solution contain these ions of zinc, silver and} copper while for the unknown solution number 2 contain Zn2+

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REFERENCE :

1. Hadariah B, Kamariah M, Sharifah Rohaiza S, (2015) Inorganic Chemistry Experiments

for Undergraduates Laboratory Manual, Experiment 1 and 2 Qualititative Analysis for Metal

Cations, Penerbit Press Universiti Teknologi Mara

2. Anne Marie H. (2016) Qualitative Analysis for Chemistry (2016) , Retrieved from

http://chemistry.about.com/od/lectureclassnotes/a/Qualitative-Analysis.htm

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