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 2014/2015 : SEMESTER 2 ACADEMIC SESSION 2014/2015 : SEMESTER 2 SCES2252/ SCES2433 : ELEKTROKIMIA ASAS/ ELEKTROKIMIA BASIC ELECTROCHEMISTRY/ ELECTROCHEMISTRY Jun 2015 June 2015 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)
1. (a) AlBr 3 tercemar dengan KF mencair dan electrolyzed. Berikan rajah sel elektrolitik dengan menunjukkan anod, katod dan arah aliran elektron. Terangkan produk elektrod berdasarkan pengetahuan tenaga pengionan dan keelektronegatifan unsur-unsur dan tulis tindakbalas separuh dan tindak balas sel keseluruhan. AlBr 3 contaminated with KF is melted and electrolyzed. Diagram the electrolytic cell by indicating the anode, cathode and the direction of electron flow. Explain the electrode products based on the knowledge of ionization energy and electronegativity of the elements and write the half-reactions and the overall cell reaction. (9 markah/marks) Tuliskan tindak balas separuh dengan menunjukkan produk yang anda ramalkan akan terbentuk dalam elektrolisis bromida emas akueus. Write the half-reactions showing the products you predict will form in the electrolysis of aqueous gold bromide. (5 markah/marks) (c) Tulis tindak balas berikut sebagai tindakbalas spontan. Kira E o cell dan aturkan tiga spesies besi dengan unitan pengurangan kekuatkan penurunan. Write the following reaction as a spontaneous reaction. Calculate E o cell and rank the the three species of iron in order of decreasing reducing strength. Fe 2+ (aq) 2Fe 3+ (aq) + Fe (s) (5 markah/marks) (d) Apabila logam kadmium menurunkan Cu 2+ dalam larutan, Cd 2+ terbentuk di samping logam tembaga. Kira nilai K dan G o pada 25 C. When cadmium metal reduces Cu 2+ in solution, Cd 2+ forms in addition to copper metal. Calculate the value of K and G o at 25 C 2. (a) Bincangkan kinetik elektrod penghasilan gas hidrogen dari larutan yang mengandungi H + (aq). Discuss the electrode kinetics of hydrogen gas evolution from a solution containing H + (aq). (7 markah/marks) 2/6
Apabila natrium hidroksida cair telah dielectrolisis menggunakan katod nikel, keupayaan lebih didapati 0.394 V untuk mengekalkan ketumpatan arus 0.01 A/cm 2 dan 0.148 V untuk mengekalkan ketumpatan arus 0.0001 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 electrolyzed using a nickel cathode, the overpotential was found to be 0.394 V to maintain a current density of 0.01 A/cm 2 and 0.148 V to maintain a current density of 0.0001 A/cm 2. Calculate the transfer coefficient and the exchange current density for the hydrogen/hydrogen ion equilibrium at a nickel cathode in the given medium. (c) Tuliskan persamaan Tafel yang diperolehi daripada persamaan Tafel Anod dan katod Tafel. Write the Tafel equation derived from Tafel Anode and Tafel Cathode equations. (d) Bincangkan fenomena pengangkutan ion atau jisim bagi 'penyebaran', 'perolakan' dan 'penghijrahan' ion atau jisim dalam larutan yang mempengaruhi kinetik tindakbalas elektrokimia. Discuss the ion or mass transport phenomena of diffusion, convection and migration of ions or mass in the solution that influence the electrochemical reaction kinetics. 3. (a) Satu sel voltan terdiri daripada setengah sel Cr/Cr 3+ dan Cd/Cd 2+ dengan semua komponen pada keadaan piawai. Selepas 10 minit operasi, lapisan nipis logam Cd telah bersalut di katod. Terangkan apa yang akan berlaku jika anda memasang terminal negatif bateri (1.5 V) untuk katod dalam sel dan terminal positif bateri kepada anod sel. A voltaic cell consists of Cr/Cr 3+ and Cd/Cd 2+ half-cells with all components in their standard states. After 10 minutes of operation, a thin coating of Cd metal has plated out on the cathode. Describe what will happen if you attach the negative terminal of a battery (1.5 V) to the cathode of the cell and the positive terminal of the battery to the anode of the cell. Apakah itu sel kepekatan? Diberi sel kepekatan berdasarkan H 2 /H + tindak balas setengah, tunjukkan bahawa ph=e cell /0.0592. What is a concentration cell? Considering a concentration cell based on the H 2 /H + half-reaction, show that ph=e cell /0.0592. (7 markah/marks) 3/6
(c) Bincangkan perbezaan diantara kaedah elektrokimia statik dan dinamik. Beri satu contoh teknik untuk setiap kaedah. Discuss the differences between static and dynamic electrochemical methods. Give one example of technique for each method. (12 markah/marks) 4. (a) Lakarkan pengujaan kronoamperometrik dan bentuk gelombang sambutan. Terangkan jawapan anda berdasarkan persamaan Cottrell. Sketch the chronoamperometric excitation and response waveforms. Explain your answer based on Cottrell equation. (12 markah/marks) Perihalkan satu eksperimen dalam voltametri siklik (CV) bagaimana untuk menganalisis dan membezakan voltamogram tindak balas elektrokimia berbalik dan tidak berbalik. Perihalkan ciri-ciri voltamogram. Describe an experiment in cyclic voltammetry (CV) on how to analyze and distinguish voltammogram between a reversible and irreversible electrochemical reaction. Describe the features of the voltammogram. (13 markah/marks) 5. (a) Bincangkan dengan lakaran bagaimana liku arus-keupayaan polarografi mencirikan perubahan penurunan proses elektrokimia tidak berbalik. Explain with a sketch how the polarographic current-potential curve characterising an electrochemical process of reduction changes when the process becomes irreversible. (10 markah/marks) Voltametri pelucutan anodik (ASV) telah dibangunkan sebagai teknik analitikal untuk ion logam berat dalam air. Anodic stripping voltammetry (ASV) was subsequently developed as a suitable analytical technique for heavy metal ions in water. (i) (ii) Perihalkan prinsip ASV dan nyatakan kenapa ia memberi kebaikan berbanding dengan polarografi. Describe the principle of ASV and state why it is advantageous compared to polarography. Lakarkan program keupayaan yang digunakan bila menjalankan experiment ASV. Sketch the potential programme used when carrying out an ASV experiment. 4/6
(iii) Namakan empat ion logam berat pencemaran toksik yang biasa ditentukan dengan menggunakan ASV. Name four common toxic pollutant heavy metal ions which can be determined using ASV. (15 markah/marks) 5/6
Apendiks Appendix TAMAT END 6/6