SCES2252/ SCES2433 : ELEKTROKIMIA ASAS/ ELEKTROKIMIA BASIC ELECTROCHEMISTRY/ ELECTROCHEMISTRY

Transcription

1 UNIVERSITI MALAYA UNIVERSITY OF MALAYA PEPERIKSAAN IJAZAH SARJANA MUDA SAINS EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE PEPERIKSAAN IJAZAH SARJANA MUDA SAINS DENGAN PENDIDIKAN EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE WITH EDUCATION SESI AKADEMIK 2015/2016 : SEMESTER 2 ACADEMIC SESSION 2015/2016 : SEMESTER 2 SCES2252/ SCES2433 : ELEKTROKIMIA ASAS/ ELEKTROKIMIA BASIC ELECTROCHEMISTRY/ ELECTROCHEMISTRY Jun 2016 June 2016 Masa : 2 jam Time : 2 hours ARAHAN KEPADA CALON : INSTRUCTIONS TO CANDIDATES : Kertas ini mengandungi 5 soalan. Jawab 4 soalan sahaja This paper consists of 5 questions. Answer 4 questions only. (Kertas soalan ini mengandungi 5 soalan dalam 6 halaman yang dicetak) (This question paper consists of 5 questions on 6 printed pages)

2 1. (a) Sel A dibina pada 25 C seperti berikut: Separuh-sel terdiri daripada pasangan Fe 3+ /Fe 2+ di mana [Fe 3+ ] = 1.00 M dan [Fe 2+ ] = M. Separuh-sel yang lain melibatkan pasangan MnO - 4 /Mn 2+ dalam larutan berasid dengan [MnO - 4 ] = 1.00 x 10-2 M, [Mn 2+ ] = 1.00 x 10-4 M and [H + ] = 1.00 x 10-3 M. Gunakan persamaan Nernst untuk mencari keupayaan elektrod untuk setiap separuh-sel dan juga keupayaan sel. A cell is constructed at 25 C as follows: One half-cell consists of Fe 3+ /Fe 2+ couple in which [Fe 3+ ] = 1.00 M and [Fe 2+ ] = M. The other half-cell involves the MnO 4 - /Mn 2+ couple in acidic solution with [MnO 4 - ] = 1.00 x 10-2 M, [Mn 2+ ] = 1.00 x 10-4 M and [H + ] = 1.00 x 10-3 M. Apply the Nernst equation to find the electrode potential for each half-cell and also the cell potential. (6 markah/marks) Bincangkan beserta sebab apa produk akan diperolehi daripada elektrolisis larutan KI akueus. Discuss with reasons what products would be obtained from the electrolysis of aqueous KI solution. (6 markah/marks) (c) Dalam sel elektrolisis akueus, ion nitrat tidak boleh bertindak balas pada anod tetapi ion nitrit boleh. Menjelaskan. In an aqueous electrolytic cell, nitrate ions never react at the anode but nitrite ions do. Explain. (3 markah/marks) (d) Jelaskan bagaimana sel kepekatan berfungsi dengan memberikan gambar rajah sel dan tindak balas sel. Describe how a concentration cell works by giving the cell diagram and the cell reactions. (10 markah/marks) 2. (a) Soda kaustik dan larutan akueus NaOH, boleh dihasilkan melalui elektrolisis garam, (NaCl) di dalam air. Terangkan proses elektrokimia ini dengan tindak balas sel. Caustic soda, an aqueous solution of NaOH, can be produced by electrolysis of table salt, NaCl, in water. Describe this electrochemical process with the cell reaction. (10 markah/marks) 2/6

3 Secara definisi, penyaduran memerlukan arus elektrik mengalir antara bahagian yang bersalut dan cecair kimia. Jika sesuatu bahagian bukan konduktif, maka arus elektrik tidak dapat mengalir. Sebagai seorang ahli elektrokimia, terangkan secara terperinci bagaimana sudu plastik boleh diberikan lapisan salutan perak di atasnya menggunakan proses elektrokimia. Tunjukkan tindak balas yang terlibat. By definition, electroplating requires an electric current to flow between the part being plated and the chemical solution. If the part is non-conductive, then an electric current cannot flow. Being an electrochemist, explain in details how a spoon made of plastic can be given a layer of silver coating on it using the electrochemical process. Show the reactions involved. (10 markah/marks) (c) Sel voltaik terdiri daripada Cr/Cr 3+ dan Cd/Cd 2+ separuh sel dengan semua komponen dalam keadaan piawai mereka. Selepas 10 minit operasi, lapisan nipis logam Cd telah bersalut pada katod. Terangkan apa yang akan berlaku jika anda sambungkan terminal negatif sel kering pada (1.5 V) katod sel dan terminal positif ke anod sel. A voltaic cell consits of Cr/Cr 3+ and Cd/Cd 2+ half-cells with all components in their standard states. After 10 minutes of operation, a thin layer of Cd metal has plated out on the cathode. Describe what will happen if you attach the negative terminal of a dry cell (1.5 V) to the cell cathode and the positive terminal to the cell anode. (5 markah/marks) 3. (a) Tulis nama dua elektrod rujukan dan terangkan mana-mana satu daripada mereka. Write the names of two reference electrodes and describe any one of them. (5 markah/marks) Bincangkan langkah penentu kadar dalam kinetik elektrod apabila Discuss the rate determining step in electrode kinetics when (i) (ii) Merujuk kepada persamaan Tafel Anod dan Tafel Katod Tafel Anode and Tafel Cathode equations are concerned Persamaan Nernst dipertimbangkan The Nernst equation is concerned. (4 markah/marks) 3/6

4 (c) Apabila natrium hidroksida cair telah dielectrolisis menggunakan katod nikel, keupayaan lebih didapati V untuk mengekalkan ketumpatan arus 0.01 A/cm 2 dan V untuk mengekalkan ketumpatan arus A/cm 2. Kira pekali pemindahan dan pertukaran ketumpatan arus untuk keseimbangan hidrogen/ion hidrogen pada katod nikel dalam medium yang diberikan. When dilute sodium hydroxide was electrolysed using a nickel cathode, the overpotential was found to be V to maintain a current density of 0.01 A/cm 2, and V to maintain a current density of A/cm 2. Calculate the transfer coefficient and exchange current density for the hydrogen/hydrogen ion equilibrium at a nickel cathode in the given medium. (4 markah/marks) (d) Terangkan jenis informasi berkenaan ion selektif logam dalam larutan yang boleh diperolehi dengan kaedah elektrokimia. Beri satu contoh teknik elektroanalitikal yang boleh digunakan dan bagaimana informasi relevan boleh didapati. Describe the types of information about selective metal ions in solution that can be obtained by electrochemical methods. Give an example of electroanalytical technique that would be used and how the relevant information would be obtained. (12 markah/marks) 4. (a) Dalam eksperimen voltametri yang dilakukan dalam larutan tidak berkacau, satu arus puncak diperhatikan, diikuti dengan penurunan perlahan arus sehingga keadaan arus tetap atau terhad dicapai. Terangkan asal usul profil arus ini. In a voltammetry experiment conducted in an unstirred solution, a sharp current peak is observed, followed by a slow reduction in current until a steady-state or "limiting" current is reached. Describe the origin of this current profile. (12 markah/marks) Lukis gambar rajah berlabel sel elektrokimia untuk eksperimen voltametri siklik. Lakarkan voltamogram dan tentukan nilai keupayaan dalam mv pemisahan di antara puncak anodik dan katodik suatu voltametri siklik satu elektron berbalik. Draw a labelled diagram of an electrochemical cell for cyclic voltammetry experiment. Sketch a voltammogram and determine the potential value in mv of the separation between the anodic and cathodic peaks of a reversible one electron cyclic voltammogram. (13 markah/marks) 4/6

5 5. (a) Jelaskan dengan lakaran gambar rajah berlabel bagaimana lengkuk aruskeupayaan polarografi mencirikan perubahan penurunan proses elektrokimia apabila proses menjadi tidak berbalik. Explain with a sketch labelled diagram on how the polarographic current-potential curve characterising an electrochemical process of reduction changes when the process becomes irreversible. (12 markah/marks) Senaraikan dan jelaskan dengan ringkas parameter, tindak balas jangkaan output dan kelebihan teknik voltametri pelucutan. Namakan empat pencemar biasa toksik ion logam berat yang boleh ditentukan dengan menggunakan voltametri pelucutan anodik. List and briefly explain the parameters, expected response output and advantages of stripping voltammetry technique. Name four common toxic pollutant heavy metal ions which can be determined using anodic stripping voltammetry. (13 markah/marks) 5/6

6 Apendiks Appendix TAMAT END 6/6