Wednesday, March 23, 2016

Tetraaminecopper(II) Sulphate - Lab Report

Bismillah.

Saya akan share lab-lab report yang mungkin sangat berguna kepada anda yang mengambil bidang Kimia. Mohon maaf sekiranya terdapat kesalahan teknikal atau tersalah kira. Mohon rujuk sumber yang lebih boleh dipercayai.

Title: Tetraaminecopper(II) Sulphate

Objectives:
1) To prepare and understand the essential conditions for the preparation and separation of tetraaminecopper(II) sulphate.
2) To determine the stoichiometry of the solid tetraaminecopper(II) sulphate by analysing the content of copper and ammonia.
3) To observe the conditions and the limitation of the technique of analysis used in the experiment.
4) To study the important properties of tetraaminecopper(II) ion complex.
5) To gain knowledgeable experience on how to handle toxical substance with care.

Introduction:
            Transition element is named like this due to their position in the periodic table, which are between the s-block and p-block. Transition element can be defined as the elements which contain partially filled d-orbital and f-orbital. All transition elements are metals which are shiny metals and good conductor of heat and electricity. For an example, copper is widely used in the manufacture of electrical wire while silver is mainly used in the industry of mirror plating due to the high properties of light reflection in silver.
            One of the features of transition element is it is paramagnetic.  This is due to the partially filled d and f subshell, that makes a high possibility that there are unpaired electrons. The second feature of transition element is it contains more than one oxidation state but not all transition elements has a variety number of oxidation states. Thirdly, transition element can form a colourful compounds. Most of the compounds formed by the transition elements contains a certain colour. This can be related to the excitation oleh electron from ground state to the excited state. Lastly, transition elements tend to form complexes.
            Copper, Cu, is a reddish-brown metal but contains thin pieces of brown colour when exposed to light. Its melting point is 1083°C in pure condition. The compound formed by copper consists of two classes, which are copper(I) and copper(II). For copper(I), the copper atom had losses one electron from valence shell, which is now give the electronic configuration of [Ar] 3d10 4s0, while for the copper(II), two electrons are removed from the outer shell and the electronic configuration is [Ar] 3d9 4s0 which is paramagnetic (Dr. Ibrahim Haji Baba 1983).
            Many of the -block elements form characteristically coloured solutions in water. For example, although solid copper(II) chloride is brown and copper(II) bromide is black, their aqueous solutions are both light blue. This is due to the hydrated copper(II) ions, [Cu(OH2)6]2+ that formed when the solids dissolve.
            The hydrated ion [Cu(OH2)6]2+ is an example of a complex, a species that has a central metal atom or ion to which a number of molecules or ions are attached by coordinate covalent bond. Coordination compound is an electrically neutral compound in which at least one of the ions present is a complex. Much research focuses mainly on the structures, properties and uses of the complexes formed between d-metal ions acting as Lewis acids and a variety of Lewis bases, partly because they participate in many biological reactions (Peter Atkins & Loretta Jones 2010).


 Chemical and Apparatus:
Chemical substances
Ammonium thiocyanate solid
CuSO4.5H2O solid
Zinc solid
Concentrated aqueous ammonia
Ethanol
Dichromate acid
2 mol/L hydochloric acid
2 mol/L sodium hydroxide
2 mol/L potassium iodide
2 mol/L barium chloride
0.1mol/L thiosulphate solution
Starch solution

Apparatus
Drying jar
Weighing bottle
Buchner funnel
250mL, 500mL conical flask
Mortar


Procedure:
A.
Preparation of the complex
Note: All of the experiments were done in the fume chamber. Any solution that contact with skin was avoided. Concentrated aqueous ammonia (14M or ‘880’ammonia) was caustic and ammonia was smelly and poisonous if smelled.
1) 20 g of CuSO4.5H2O was grinded into powder in a mortar.
2) Then it was dissolved in the mixture of concentrated aqueous ammonia (30 mL) and water (20 mL). The temperature must not exceeded 35°C during the mixing process.
3) Dark blue homogen solution was formed.
4) 10 mL of ammonia solution was added before filtration process was done, if there was a precipitate formed. 40 mL of ethanol was added slowly while stirring the solution. The temperature must controlled by not exceeding 35°C.
5) Dark blue crystalline precipitate was formed.
6) The precipitate was isolated by using Buchner funnel.
7) The precipitate was washed with a mixture of 40 mL ethanol and 10 mL concentrated aqueous ammonia. It was dried by air on the Buchner funnel for 5 minutes.
8) The precipitate was dried in a drying jar which contained silicon gel before it was weighed and analysed.
9) The drying process was done for about 12 to 20 hours.
10) The weight of the product was recorded and the percentage yield was calculated.

Reaction with Complexes
1) The solid was heated in fume chamber. Then the gas released was tested by litmus paper. Any smell inhaled was recorded. The gas was then testes with filter paper that has been dipped in a dichromate acid solution.
2) A small amount of the complex was dissolved in water. The test was done by using litmus paper. The solution was heated.
3) Another small amount of the complex was dissolved in diluted hydrochloric acid solution (2 mol/L) and it was heated.
4) Another small amount of complex was dissolved in diluted sodium hydroxide solution and it was recorded.
5) Another small amount of complex was dissolved in distilled water. The solution was divided into two test tubes A and B. A small amount of hydrochloric acid was poured into test tube A. H2S gas was passed through each of the test tubes.
6) Another small amount of complex was dissolved in distilled water and 2 mol/L of barium chloride was added into it.

B. Analysis of Complex
i. Preparation of stock solution for the analysis
1. 5 g of complex was weighed accurately after dried. It was then put inside a 500 mL volumetric flask.
2. The complex was dissolved in a small amount of about 20 mL distilled water and 50 mL 2 mol/L diluted hydrochloric acid by using measuring cylinder. A clear solution with faint blue colour was formed.
3. 2 mol/L hydrochloric acid was added drop by drop if there was precipitate formed until the precipitate disappeared. The final solution must be in an acidic condition, and this was tested and confirmed by using litmus paper.
4. The volume was increased  to 500 mL by adding distilled water to the calibrated mark. This solution existed in stable state and can be used for a few weeks.
5. The complex was analysed for copper and ammonia, which was done for three times.
6. 50 mL of the sample solution was used in the determination of copper via iodometry and 25 mL of the sample solution for ammonia analysis.

ii. Determination of copper by volumetric analysis
1. 50 mL of the sample solution was transferred into 250 mL conical flask.
2. Ammonia was added until a complete precipitate was formed.
3. 3 mol/L of acetic acis was added drop by drop until the precipitate was completely dissolved.
4. 15 mL of 10% potassium iodide was added and it was titrated with 0.1 M standard thiosulphate solution until the brown colour of the iodine turned to pale yellow.
5. 2 mL of prepared starch solution was added and the titration was continued until the blue colour almost disappeared.
6. Solid ammonium thiocyanate (1 to 2 g) was added to absorb the iodine from CuI and the titration was continued until the last drop showed the changing from blue colour to white yellow.
7. The overall volume of thiosulphate that has been used was recorded.
8. The percentage of copper in the sample was calculated from the three titrations that have been done.

iii. Detemination of ammonia by volumetric analysis
1. Distillation apparatus was set up. Grease was usedon every joints of the distillation apparatus.
2. 25 mL of sample solution was added into the distillation jar, and distilled water was added until the volume became 100 mL. A few zinc marbles were added into it.
3. 10 mL of 20% sodium hydroxide solution was addded into the distillation jar.
4. 50 mL of standard hydrochloric acis (0.1 mol/L) was added into the absorption jar and it was connected quickly with the other parts.
5. The distillation was started and continued until 75% contents in the distillation jar was completely distilled.
6. The excess acid was titrated with prepared 0.1 mol/L sodium hydroxide solution and phenolphthalein was used as the indicator.
7. The percentage of ammonia in the sample was calculated from the three distillations that have been done including the expected errors.


Result:
I. Preparation of complex
Mass of CuSO.5HO solid (g)
20.03
Mass of filter paper (g)
0.3300
Mass of petri dish (g)
38.03
Mass of complex + filter paper + petri dish (g)
55.05
Mass of complex (g)
16.69

The chemical equation for the production of tetraaminecopper(II) sulphate complex is,
CuSO.5HO + 4NH →  [Cu(NH)]SO.HO + 4HO
Number of moles of CuSO.5HO, n is,
n  =      mass of substance/molecular weight of substance
 =         20.03/[63.54g/mol+32.06g/mol+(4×16.00g/mol)+5(2(1.008g/mol)+16.00g/mol)]
 =      0.08022 mol
0.08022 mol of CuSO.5HO ≡ 0.08022 mol of [Cu(NH)]SO.HO

Mass of [Cu(NH)]SO.HO,
= 0.08022 mol × [63.54g/mol + 32.06g/mol + (4×16.00g/mol) + 4(14.01g/mol + (3×1.008g/mol)) + (2×1.008g/mol) + 16.00g/mol]
= 19.71 g
Theoretical yield = 19.71 g
Actual yield = 16.69 g
Hence, percentage yield,
= (actual yield)/(theoretical yield) * 100%
= 16.69 g/19.71 * 100%
= 84.68 %


II. Reactions with complex

Test
Observation
Conclusion
A
The solid was heated and the gas released was tested by using litmus paper, followed by filter paper that had been dipped in dichromic acid.
The dark blue solid was turned into light blue colour. There was a punget smell. Blue litmus paper did not change its colour. The orange colour of filter paper was turned into orange.
The equation of this reaction is, [Cu(NH3)]2+(s) Cu2+(aq)+4NH3(g)
The no change in the colour of blue litmus paper is due to the alkali properties of the ammonia.
B
The complex was dissolved in distilled water and tested by using litmus paper, and then followed by heating.
A pale blue solution was formed. Blue litmus paper did not change its colour. There was an efferverscence when heated.
The equation of this reaction is,
NH4++OH­­-→NH3+H2O
The no change in the colour of blue litmus paper is due to the alkali properties of the ammonia.
C
The complex was dissolved in diluted hydrochloric acid solution, and was heated.
Blue litmus paper was turned into red colour. The blue solution was turned into yellowish. A green precipitate was formed. Effervescence occured when heated and it was turned into cloudy blue solution.
The green solution was due to the [CuCl4]2+ ion. The change of colour from blue to red colour in the litmus paper was due to the acidity of solution.
D
The complex was dissolved in diluted sodium hydroxide solution and was heated.
Blue litmus paper did not change its colour. The blue solution was turned into cloudy blue. A pungent smell was released. Effervescence occured when heated, and the solution was turned into dark-blue colour.
This shows that the tetraaminecopper(II) sulphate is a basic complex. It gives ammonia gas when heated.
E
The complex was dissolved in distilled water, and was divided into two parts, one part is acidified.
Both were then tested with HS gas that passed through.
The solution turned into yellowish-green, and then turned into brown. A brown precipitate was formed.
The equation of this reaction is
Cu2+(aq) + 4I-(aq) ==> 2CuI(s) + I2(aq)
Brown solution indicates the present of iodine.
F
The complex was dissolved in water, and was divided into two parts, one part is acidified. Both were added with 2 mol/L potassium iodide.
White precipitate formed in the acidic solution. For the other solution, the blue colour solution was changed into green.
Copper metals formed a coordination bond with iodine ligand, resulting in the changes in colour and form precipitate.
G
The complex was dissolved in distilled water, and barium chloride was added.
No apparent changes were seen. Effervescence occured.
The milky blue solution formed was BaSO4(s).
The equation of this reaction is,
Ba2+(aq)+SCu2-(aq)→BaSO4(s)



III. Complex analysis
i. Preparation of stock solution for analysis
Mass of petri dish                                           = 37.64 g

Mass of petri dish + product [Cu(NH3)4SO4] = 42.66 g

Mass of product [Cu(NH3)4SO4]                    = 5.02g

ii. Determination of copper via volumetric analysis (iodometry)
Titration
I
II
III
Initial reading (mL)
0.00
18.2
0.00
Final reading (mL)
18.2
36.8
22.7
Volume used (mL)
18.2
18.6
22.7

Average volume of thiosulphate solution used =  (18.2 + 18.6 + 22.7)/3 mL
                                                               =  59.5/3 mL
                                                               = 19.83 mL
iii. Determination of ammonia via volumetric analysis        
Titration
I
II
Initial reading (mL)
1.8
4.1
Final reading (mL)
4.1
4.8
Volume used (mL)
2.3
0.7

Average volume of sodium hydroxide solution used
                                       = ((2.3 + 0.7)/2 mL
                                       =  3/2 mL
                                       = 1.5 mL


Data Analysis:
A. i. Preparation of complex
2 M BaCl
gm = molecular weight * molarity * volume * 100/p
      = 244.28 x 2M x 1L x 100/99
      = 493.46 g in 1 L
      = 49.346 g in 100 mL
0.01 M dichromate acid
gm = molecular weight * molarity * volume * 100/p
      = 294.19 x 0.01 x 1 L x 100/99
      = 2.9716 g in 1 L
      = 0.29716 g in 100 mL

B. i. Preparation of stock solution for analysis
Mass of petri dish (g)
37.65
Mass of petri dish + product [Cu(NH3)4SO4] (g)
42.65
Mass of [Cu(NH3)4SO4] used (g)
5.02
Mass of [Cu(NH3)4SO4] used (g)
5.02

Number of moles of [Cu(NH3)4SO4] used     = (Mass of [Cu(NH3)4SO4] used)/(Molar mass of [Cu(NH3)4SO4])
                                                                        = (5.02 g) / (227.77 g/mol )
                                                                        = 0.022 mol
Volume of solution    = 500 mL
                                    = 0.50 dm3
                                    = 0.50 L

Concentration of solution , M =  (Number of moles of [Cu(NH3)4SO4]) / (Volume of solution)
                                                = (0.022 mol) / (0.50 L)
                                                = 0.044 mol/L
ii. Determination of copper by volumetric analysis
2Cu2+(aq) + 5I-(aq)     à    2CuI(s) + I3- (aq)
I3-(aq)+ 2S2O32-(aq)      à   3I-(aq) + S4O62- (aq)

2 mol Cu2+ produce 1 mol I3-

1 mol I3- reacts with 2 mol S2O32- to form 3 mol I- and S4O62-
1 mol Cu2+ is stoichiometric to 1 mol S2O32-


Total volume of thiosulphate solution used = 59.5 mL
Concentration of standard thiosulphate solution = 0.1 mol/L


Number of moles of SOз²ˉ used = MV/1000
                                                     = (0.1 mol/L  * 59.5 mL)/1000
                                                     = 0.00595 mol
Number of moles of Cu²+ ion in 500 mL solution =  (0.00595 mol * 500 mL)/(50 mL)
                                                                                = 0.0595 mol

Mass of Cu2+ ions in 500 mL solution = 0.0595 mol * 63.55 g/mol
                                                             = 3.78 g
Percentage of Cu2+ ions in 5.00 g of [Cu(NH3)4]2+ sample = (3.78g)/(5.00 g)  x 100%
                                                                                            = 75.6 %
Number of moles of 5.00 g of [Cu(NH3)4]2+  = (5.00 g)/(63.55+68.04 g/mol)    
                                                           =  (5.00 g)/(131.59 g/mol)
                                                           = 0.038 mol

1 mol of [Cu(NH3)4]2+ has 63.55 g of Cu2+ and 68.04 g (NH3)4 
0.038 mol of [Cu(NH3)4]2+  =  (63.55 g × 0.038 mol)/( 1 mol)      
                                            = 2.41 g Cu2+


Theoretical value of Cu2+= 2.41 g
Experimentally value obtained of Cu2+ = 3.78 g

iii. Determination of ammonia by volumetry analysis
HCl (aq) + NH4OH(aq)    à          NH4Cl (aq)+ H2O (l)

HCl (aq) + NaOH (aq)       à         NaCl (aq) + H2O (l)

           
Total volume NaOH used in titration            =  3.00 mL
Concentration of NaOH used in titration       = 0.1 mol/L
Number of moles of NaOH used        = MV/1000
                                                            = (0.1 mol/L  * 3.00 mL)/1000                         
                                                            = 0.0003 mol

1 mol of HCl   is stoichiometric to  1 mol of NaOH
0.0003 mol of NaOH reacts with 0.0003 mol of HCl

Volume of standard HCl                    = 50 mL
Concentration of standard HCl          = 0.1 mol/L
Number of moles of HCl produced    = MV/1000
                                                             = (0.1 mol/L  * 50 mL)/1000
                                                             = 0.005 mol

Number of moles of HCl that reacts with NaOH = 0.005 mol - 0.0003 mol
                                                                  = 0.0047 mol

1 mol of HCl reacts with 1 mol of aqueous ammonia
Number of moles of ammonia produced = 0.0047 mol in 25 mL sample

Number of moles of ammonia in 500 mL solution = (0.0047 mol * 500 mL)/(25 mL)
                                                                                                  = 0.094 mol

Mass of NH3 = Number of moles of NH3  *  Molar mass of NH3
                      = 0.094 mol * [14.01 + 3(1.01)] g/mol.
                      = 0.094 mol * 17.04 g/mol
                      = 1.60 g

Percentage of NH3 in [Cu(NH3)4] 2+ = (1.60 g)/(5.000 g)  * 100 %
                                                         = 32 %

5.00 g of [Cu(NH3)4]2+ contain 0.038 mol, in 1 mol of [Cu(NH3)4]2+, there is 68.04 g (NH3)

In 0.038 mol of [Cu(NH3)4]2+, theoretically, (68.04 g * 0.038 mol)/1mol
                                                  = 2.59 g

Experimental value of (NH3)4 produced = 1.60 g
The difference between experimental value and theoretical value
= 2.59 g – 1.60 g
= 0.99 g


Discussion:
            Transition elements can be defined as a metal that can form at least one ion which has a partially-filled d-subshell. One of the uniqueness of transition elements is the variety of oxidation states. They can form complex ions which have empty orbitals that can receive electron pair from the ligands. Besides, they can form colourful compounds due to the transition of the electrons occcured in the partially-filled d-subshell. Transition elements may also serve as a catalyst in the chemical industry. (Kho Chin He 1989).
            The chemistry of copper can be divided into copper(I) and copper(II). Copper(I)  is much more stable than copper(II). Some of the copper(II) compounds are not stable due the the easy-oxidized ion, for example copper(II) iodide, copper cyanide and copper(II) thiocyanate are spontaneously decomposed to copper(II) compounds in room temperature. Meanwhile, copper(I) complex is a stable copper compound which is soluble in water. This complex ion can be formed from two types of complex. Cation complexes, for example is [Cu(NH3)2]+and for the anion complexes are [Cu(Cl)2]- and [Cu(CN)4]3-.
            Copper(II) compound can form a group of stable complexes. Tetraaminecopper(II) ion, [Cu(NH3)2]2+ is commonly contains six ligands, however two of its ligands are far away from it compared to the other four ligands, which give a octahedron shape. Therefore, [Cu(NH3)2]2+ is suitable to be represented as [Cu(NH3)4(H2O)2]2+ (Dr. Ibrahim Haji Baba 1983).
            In this experiment, the tetraaminecopper(II) sulphate complex is prepared by mixing hydrated copper(II) sulphate with ammonia and is undergo separation process via Buchner funnel in the presence of air vacuum. After 24 hours, the complex is fully dried in a dry jar consists of silica gel.
            From the several tests of tetraaminecopper(II) sulphate complex, it is found that the complex has a high alkaline properties. This can be observed from the presence of ammonia in the compound. When heated and tested with red litmus paper, its colour changed into blue colour, indicates that it is an alkali. Besides, the strong pungent smell also give a strong evidence that the compound contains the easily vaporised ammonia.   
            For the analysis of copper and ammonia in tetraaminecopper(II) sulphate complex, we use iodometry technique to determine the presence of targeted entities. For the identification of copper, the tetraaminecopper(II) sulphate solution is titrated with the standard thiosulphate. At first, we failed to get a proper result for the titration. This is due to the contamination of potassium iodide which may influence the process of titration.
            In the determination of ammonia, the complex is firstly undergo distillation process. Zinc marbles are added in the distillation jar to avoid superheating. The excess acid obtained is now titrated with sodium hydroxide. Phenolphthalein is added as the titration indicator. We failed to get the second result of titration due to the absence of phenolphthalein, therefore only 2 results of titration are succesfully obtained.
            To avoid these errors in the future, one should make sure all substances and indicators are added before conducting the next steps. To handle toxical chemical substances, gloves and goggles should be wear during the laboratory session. All waste substances should be discarded in the proper jar.


Conclusion:
The preparation of tetraaminecopper(II) sulphate can be expressed in the following equation,
CuSO4.5H2O (s) + 4NH3 (aq)      à              [Cu(NH3)4] SO4 (s) + 5H2O (l)

The percentage of complex produced is 84.68 %.

The percentage mass of Cu2+ ion in complex is 75.6%.

The percentage mass of NH3 in complex is 32 %.




Questions:
1. Aqueous ammonia always referred as ammonia “8-80” because the density of the solution is 0.880 g/mL. If the solution contain only 27% mass of NH3, what is the estimated molarity?
Density = 0.880 g/mL
1 mL of solution contains 0.880g of NH3
27% NH3 contains = (0.880 * 27∕100) g NH3 = 0.2376 g NH3

In 1 mL of solution, number of moles of NH3 = 0.2376/17.03
                                                                          =1.395 * 10-2 mol NH3

In 1000 mL of solution = (1.395 * 10-2) * 1000
                                      = 13.95 mol NH3

Molarity of NH3 = 13.95 mol/L

2. Explain why it is important for copper iodide to have a low solubility in the iodometry analysis? How starch can be functioned as an indicator in the titration of iodine with thiosulphate?
The reason of copper iodide to have a low solubility in the iodometry analysis is due to the comparison of standard potentials for copper and iodine. As the concentration of Cu+ ions in solution is very low, consequently the standard potential of the process Cu2+/Cu+ is much higher. There is excess of iodide cations in solution. The reaction which is observed when I-ions are added to Cu2+in solution is 2Cu2++ 4I- à 2Cu (precipitate) + I2 and one observes that the stoichiometric amount of iodine is formed.
During iodine titrations, concentrated iodine solutions reacted with thiosulphate in order to remove most of the iodine before the starch is added. This is due to the starch-iodine complex which may prevent some of the iodine reacting with the titrant. Near the end-point, the starch is added, and the titration process is resumed taking into account the amount of thiosulphate added before adding the starch.
3. What is the role of the zinc marbles added into the distillation jar for the ammonia analysis?
The role if the zinc marbles added into distillation jar is to lower the bumping during distillation. The zinc will react slowly with ammonia to produce effervescence of hydrogen gas to prevent superheating of the liquid.


References:
Atkins and Jones. 2010. Chemical Principles; the quest for insight (5th ed.). New York: W.H. Freeman and Company. Page 680.
Dr. Ibrahim Haji Baba. 1983. Unsur-unsur Peralihan. Kuala Lumpur: Penerbitan Mahakarya. Page 47.

Kho Chin He. 1989. Kimia Bukan Organik. Kuala Lumpur: Federal Publications. Page 94.

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