E12 10004 2021 Student Report Template (Auto Recovered) PDF

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REPORT COVER SHEET AND DECLARATION School of Chemistry The University of Melbourne Laboratory Report Cover Sheet Student Name: Student Number: Subject Name & Code: Demonstrator: Experiment Title:

Meraal Zaib 1268766 CHEM10004 Jacob Rowan Experiment 12: Coordination Chemistry – Synthesis of Hexaamminecobalt(III) Chloride.

Due Date: _________13th October 2021____________________ By submitting work for assessment, I hereby declare that I understand the University’s policy on academic integrity and I declare that: • This laboratory report is my own original work and does not involve plagiarism or unauthorised

collusion, except where due credit is given to the work of others. The report is based on results and spectra obtained by me during my laboratory session. • This laboratory report has not previously been submitted for assessment in this or any other subject. For the purposes of assessment, I give the assessor of this assignment the permission to: • Reproduce this laboratory report and provide a copy to another member of staff; and • Take steps to authenticate the assignment/laboratory report, including communicating a copy of this assignment to a checking service (which may retain a copy of the assignment on its database for future plagiarism checking). Feedback on Report: Feedback on your report and the mark you received will be available on the Online Practical Assignments page on Canvas. Plagiarism: Plagiarism is the act of representing as one's own original work the creative works of another, without appropriate acknowledgment of the author or source. Collusion: Collusion is the presentation by a student of an assignment as his or her own work, but which is in fact the result in whole or in part of unauthorised collaboration with another person or persons. Collusion involves the cooperation of two or more students in plagiarism or other forms of academic misconduct. Both collusion and plagiarism can even occur in group work. For examples of plagiarism, collusion and academic misconduct in group work please see the University’s policy on Academic Honesty and Plagiarism: https://academichonesty.unimelb.edu.au Plagiarism and collusion constitute cheating. Disciplinary action will be taken against students who engage in plagiarism and collusion as outlined in University policy. Proven involvement in plagiarism or collusion may be recorded on your academic file in accordance with Statute 13.1.18.

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Experiment 12: Coordination Chemistry – Synthesis of Hexaamminecobalt(III) Chloride. Author(s): Meraal Zaib Day/Time/Group number: Tues/2pm/21 Abstract: (Summary of what you did and what you found out) In this experiment, a typical coordination complex, hexaamminecobalt(III) chloride, [Co(NH3)6]Cl3 was synthesised, with a 31% actual yield. While a ligand’s strength is influenced by basicity and denticity, the ligand substitution rates were determined to be labile (fast) or inert (slow). As ligand substitution and oxidation rates with metal ions produced a change in colour, the reactions were observed with the naked eye. In part A, Co(II) sulphate was dissolved in water, where labile ligand substation and then oxidation occurred producing hexaammine cobalt(II) chloride, which was then cooled to form crude crystals. In part B, the purification process via recrystallisation of the curde crytsals involved the addition of hot dilute HCl, hydrating the cobalt ions, the chlorine ions force the water out of the water complex of cobalt. Several test tube reactions were completed with Co(III), Co(II) and Ni(II) complexes, and colour changes were observed with the naked eye to determine whether ligand exchange had occurred.

Introduction and Aim: (What is a coordination complex? Why are they of interest? Which metals are most commonly involved? What is the most common geometry?) When a metal ion is coordinated by a certain amount of ligands, this molecule is called a coordination complex and it is critical to many applications in civilisation. Arising from an Lewis acid/base reaction whereby ligands, neutral or charged, form coordinate bonds with a central metal atom in a transfer of electrons between compounds via a redox reaction. From their advantagous implementation primarily in industrial uses as catalysts, and medicine. More significantly understanding the coordination chemistry that occurs inside living bodies have helped in the development of anti-cancer treatments, such as cisplatin. For instance, understanding how a haem group carries oxygen in blood. Apart from medical uses, coordination compinds are also useful in synthesizing new materials, some with biological applications. The most common metals are cobalt, iron, scandium, titanium, vanadium, chromium, manganese, and nickel, with the most common geometry being octahedral, where six ligands are coordinated to the metal, increasing its denticity and thus stability.

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Experimental: (How did you perform your experiment?) Refer to Lab manual.

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Results and Discussion: REMEMBER TO SHOW ALL WORKING FOR CALCULATIONS AND TO SUPPORT YOUR ANSWERS WITH EXPERIMENTAL EVIDENCE OR THEORY Part A and B. Synthesis of hexaamminecobalt(II) chloride. Question 1 What characteristic is essential for a molecule to act as a ligand? Must have basicity and have at least one donor atom with an electron pair used to form covalent bonds with the central atom.

Yield Mass of hexamminecobalt(III) chloride: 0.22 g a) Calculate the theoretical yield of hexaamminecobalt(III) chloride based on the no. of mole of CoSO4 7H2O used. 1:1, n(hexamminecobalt(III) chloride): n(cobalt sulfate heptahydrate) m(CoSO47H2O) = n*M = 2.66*10-3 mol* 267.48 g mol-1 = 0.711 g b) Express your actual yield as a percentage of the theoretical yield. Actual yield/theoretical yield*100% = 0.22 g / 0.711 g*100% = 31%

Part C: Test Tube Reactions of Co(III) and Co(II) and Ni(II) Complexes Record your observations and write an ionic equation for any overall reaction, or No Change, as required. Test 1 Observations Overall Reaction equation Test 2 Observations

Overall Reaction equation

Reactions of Co(III) complex

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[Co(NH3)6]Cl3, add AgNO3

Before the silver nitrate is added, the solution is yellow, after addition of AgNO3, the solution turns darker yellow and a faint white precipitate can be seen forming. The solution becomes more opaque over time. Co3+ (aq) + Ag (s) + Cl- (aq)  Ag2Co (s) Reactions of Co(III) complex  [Co(NH3)6]Cl3, add i)heat and ii)NaOH i)heat No change to colour of litmus paper. The vapours are neutral in pH, could be water vapour. ii)add NaOH Overtime, the solution turned dark brown, and developed a black precipitate. i)heat No reaction. ii)add NaOH Co3+ (aq) + 2NaOH- (aq)  Co(OH)3 (s) + NaCl (aq)

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Test 3 Observations

Explanation

Test 4

Reactions of Co(II) complex  [Co(OH 2)6]2+(aq) ion: stabilization energy 2[Co(OH2)6]2+ (aq) + 4Cl- (aq)[CoCl ⇋ (aq) + 6H2O (l) 4] Add HCl: Colour of cobalt went from orange to a rose, mauve colour. Adding more HCl, the solution then turned blue/purple. Cool: The solution turned more transparent and lighter purple in colour. Heat: The solution turned bright blue (colour it was when adding HCl) (Effect of heat, identify species formed on heating) The effect of heating the solution shifted the equilibrium to the right. By favouring the formation of the product ([CoCl 4]2-). The colour of the solution becomes what it was when adding HCl. Heating will favour the tetrahedral complex. Reactions of Co(II) complex  [Co(OH2)6]2+(aq) ion: concentration effect

Observations

Add HCl: Pink solution turns light blue Add water: The dilution with water resulted in the solution turning pink.

Explanation

(Effect of HCl, identify species formed) The increase in chlorine ions will mean the eqiulbiruim will try to decrease chlorine concentration by pushing the reaction to the left. Le Chaterlier’s principle explains the shift of the equilibrium to the left as an increase in chlorine ions will favour the production of [Co(OH2)6]2+, or Co(II) which is blue in dry form. Reactions of Ni(II) complex, add NH3

Test 6 Observations

Overall Reaction equation

Add water: A cyan solution forms. Add NH3: The solution turns cyan to a bright blue. A clear layer is visible at the top of the test tube, indicating the volatility of the ammonia. Ammonia replaces (displacement), which pushes the reaction forward. Add ethylenediamine: (Passive diffusion) The solution turns purple/violet after shaking. Heat: While a layers formed indicating competition between species, after mixing, test tube 1 contained a deeper purple solution, while test tube 2 was lighter purple. Add NH3: [Ni(H2O)6]2+ (aq) + 6NH3 (aq)  [Ni(NH3)6]2+ (aq) + 6H2O (l) Add ethylenediamine: [Ni(NH3)6]2+ (aq) + 3(en) (l)  [Ni(en)3]2+ (aq) + 6NH3 (aq) Heat: No reaction

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Test 7

Reactions of Ni(II) complex, add ethylenediamine

Observations

Add water: The solution is cyan in colour. Add ethylenediamine: Solution is purple/violet in colour. Add NH3: The solution turns lighter purple. Heat: Before mixing, there is a lighter purple layer at the top, while a darker sediment stays at the bottom. After mixing, the colour is relatively light violet.

Overall Reaction equation

Add ethylenediamine: [Ni(H2O)6]2+ (aq) + 3(en) (l)  [Ni(en)3]2+ (aq) + 6NH3 (aq) Add NH3: No reaction Heat: No reaction

Question 2 For Test 3, equation below, label the forward direction as exothermic or endothermic. Explain your answer using Le Chatelier’s Principle. 2[Co(OH2)6]2+ (aq) + 4Cl- (aq) [CoCl ⇋ (aq) + 6H2O (l) 4] Forward reaction is endothermic, while the backward reaction is exothermic and favoured. According to Le Chatelier’s principle, [Co(OH2)6]2+ is octahedral and more stable, thus is produced. As the concentration of reactants increase, the system will act to produce a stable ligand. A complex is more stable if a bidentate or multidentate ligand replaces a monodentate due to the increase in entropy.

Question 3 Draw the 3 coordination complexes formed in Test 6, beginning with the Ni(II) complex in water. Complex 1: Complex 2: Complex 3:

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Question Provide an explanation for the results of Tests 6 and 7: i.compare the ligands H2O, NH3 and ethylenediamine – which one is most easily substituted?) ii. which is the most stable complex and why? The rate of substitution of H2O is relatively high than ammonium, and ethylenediamine, making it a labile reaction. Complex 3 is more stable as the number of ligands bound to it are greater. Complex 3 is a chelate, which have greater denticity, and are thus more stable than the analgous monodentate ligands. Multidentate ligands can bind more tightly because of the chelate effect. As the enthalpy influences how strongly entropy affects a molecule, the entropy going from complex 1 to complex 3 is greater. The reaction is not spontaneous as there is a small entropic barrier, since entropy is relatively small compared to enthalpy. Additionally, the bidente ligand is stronger than monodentate. Complex 3 is relatively more stable than complex 2, as there is a more negative enthalpy change. And further adding to the stability of complex 3 is its higher equilibrium constant than complex 2.

Conclusion: (What have you found out?) In sum, the synthesis of hexaamminecobalt(III) chloride, the mass of hexamminecobalt(III) chloride being 0.22 g, had a 31% actual yield relative to the number of moles of cobalt sulfate heptahydrate (0.00266 mol) used. Consequently, the lability of reactions with cobalt(II), cobalt(III) and nickel(II) were determined while ligand exchanges were compared according to the denticity and stability of the compounds that were formed. With the test tubes reactions involving heating, cooling, and the addition of HCl, NaOH, or water. The addition of heat worked to break intermolecular bonds, though some atoms formed stronger bonds. The findings of the experiment revealed that a more stable coordinate complex will form as a result of it being multidentate, or chelate, and replaces monodentate ligands, such as H 2O in metal aquo complexes by NH3, and NH3 by ethylenediamine. Le Chaterlier’s principle was used as the basis for predicting the production of a more stable octahedral complex.

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