UNIVERSITY OF MALAYA UNIVERSITI MALAYA EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE PEPERIKSAAN IJAZAH SARJANA MUDA SAINS EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE WITH EDUCATION PEPERIKSAAN IJAZAH SARJANA MUDA SAINS DENGAN PENDIDIKAN ACADEMIC SESSION 2011/2012 : SEMESTER 2 SESI AKADEMIK 2011/2012 : SEMESTER 2 SCES2252/ SCES2433 : BASIC ELECTROCHEMISTRY/ ELECTROCHEMISTRY ELEKTROKIMIA ASAS/ ELEKTROKIMIA June 2012 Jun 2012 TIME : 2 hours MASA : 2 jam INSTRUCTIONS TO CANDIDATES : ARAHAN KEPADA CALON : This paper consists of 5 questions. Answer 4 questions only. Kertas ini mengandungi 5 soalan. Jawab 4 soalan sahaja (This question paper consists of 5 questions on 7 printed pages) (Kertas soalan ini mengandungi 5 soalan dalam 7 halaman yang dicetak)
SCES2252/SCES2433/02 1. (a) Combine the following two half-reactions into a balanced equation for spontaneous reaction and calculate E o cell. Gabungkan dua tindak balas setengah berikut ke dalam persamaan tindak balas spontan yang seimbang dan kira E o cell. i. NO 3 - (aq) + 4 H + (aq) + 3e - NO (g) + 2H 2 O (l) E o = + 0.96 V ii. MnO 2 (s) + 4 H + (aq) + 2e - Mn 2+ (aq) + 2H 2 O (l) E o = +1.23 V A concentration cell consists of two Ag/Ag + half-cells. In half-cell A, electrode A dips into 0.010 M AgNO 3 ; in half-cell B, electrode B dips into 4.0X10-4 M AgNO 3. Calculate the cell potential at 298 K and show which electrode will have a positive charge. Sel kepekatan mengandungi dua sel setengah Ag/Ag +. Pada sel-separuh A, elektrod A dicelup dalam 0.010 M AgNO 3 ; dalam sel-separuh B, elektrod B dicelup dalam 4.0X10-4 M AgNO 3. Kira keupayaan sel pada 298 K dan tunjukkan elektrod yang akan mempunyai cas positif. (c) Explain with the electrochemical reactions what will happen at the hulls and anchors of ocean-going vessels if it is not painted. Terangkan dengan tindak balas elektrokimia apa yang akan berlaku pada badan kapal dan sauh kapal lautan jika ia tidak dicat. (d) Sodium hydroxide and chlorine are widely used in our everyday life. Describe the electrochemical chlor-alkali process for their production. Natrium hidroksida dan klorin digunakan secara meluas dalam kehidupan seharian kita. Huraikan proses elektrokimia klor-alkali untuk penghasilannya. (10 marks/markah)
SCES2252/SCES2433/03 2. (a) Black-and-white photographic films are coated with silver halides. Because of silver is a heavy metals which pollutes the environment, the manufacturers monitor [Ag + ] waste of the waste stream from the plant with a Ag + -selective electrode at 25ºC. A stream of known [Ag + ] standard is passed over the electrode in turn with the waste stream and the data is recorded with a computer. Calculate the concentration of silver waste, [Ag + ] waste, if E waste is 0.003 V higher than E standard and the standard contains 1000 ng/l. Filem fotografi hitam putih disalut dengan halida perak. Disebabkan perak adalah logam berat yang mencemarkan alam sekitar, pengeluar mengawal [Ag + ] aliran sisa dari kilang dengan elektrod Ag + -terpilih pada 25 ºC. Suatu aliran yang diketahui [Ag + ] piawai melewati elektrod dengan aliran sisa dan data direkodkan dengan komputer. Kirakan kepekatan sisa perak, [Ag + ] sisa, jika Ewaste adalah 0,003 V lebih tinggi daripada Estandard dan standard mengandungi 1000 ng / L. In a test of a new reference electrode, a chemist constructs a voltaic cell consisting of a Zn/Zn 2+ half-cell and a H 2 /H + half-cell under the following conditions: Dalam ujian elektrod rujukan yang baru, seorang ahli kimia membina sebuah sel yang terdiri daripada sel setengah Zn/Zn 2+ dan sel setengah H 2 /H + di bawah keadaan berikut: [Zn 2+ ] = 0.010 M [H + ] = 2.5 M and P H2 = 0.3 atm. Calculate E cell at 298 K. Kira pada 298 K. (c) Lead can displace silver from solution: Plumbum boleh menggantikan perak dari larutan: Pb (s) + 2Ag + (aq) PB 2+ (aq) + 2Ag (s) As a consequence, silver is a valuable by-product in the industrial extraction of lead from its ore. Calculate K and Gº at 25ºC for this reaction. Akibatnya, perak adalah produk sampingan yang bernilai dalam pengekstrakan perindustrian plumbum daripada bijihnya. Kira K dan Gº pada 25 ºC bagi tindak balas ini. (6 marks/markah)
SCES2252/SCES2433/04 (d) Discuss the three forms of mass transport in an electrochemical reaction. Bincangkan tiga bentuk pengangkutan jisim dalam tindak balas elektrokimia. (9 marks/markah) 3. (a) Show how the electrical current on an electrode depends on the electrode potential in Butler-Volmer equation. Tunjukkan bagaimana arus elektrik pada elektrod bergantung kepada keupayaan elektrod dalam persamaan Butler-Volmer. (3 marks/markah) Describe standard hydrogen electrode (SHE) Jelaskan elektrod hidrogen piawai (SHE) (c) Define the followings: Takrifkan yang berikut: i. Working electrode Elektrod kerja ii. iii. Counter electrode Elektrod kaunter Reference electrode Elektrod rujukan (4.5 marks/markah) (d) Discuss the differences between potentiometry and voltammetry measurements. Bincang perbezaan di antara pengukuran potentiometry dan voltammetry. (12.5 marks/markah)
SCES2252/SCES2433/05 4. (a) Sketch the cyclic voltammogram for a mixture of two reversible 1 electron species, ox 1 and ox 2, with E o s separated by 300 mv (E o ox1 = E o ox2 + 300 mv) for D ox1 = D ox2 and [ox 1 ] = [ox 2 ]. On the same diagram, sketch the cyclic voltammogram for a mixture of ox 1 and ox 2 when E o s are different by 5 mv. Lakarkan cyclic voltammogram untuk spesis 1 elektron campuran dua tindak balas berbalik, ox 1 dan ox 2, dengan E o s dipisahkan oleh 300 mv (E o ox1 = E o ox2 + 300 mv) di mana D ox1 = D ox2 dan [ox 1 ] = [ox 2 ]. Dalam rajah yang sama lakarkan cyclic voltammogram untuk campuran ox 1 dan ox 2 bila E o s berbeza sebanyak 5 mv. (15 marks/markah) Sketch the chronoamperometric excitation and response waveforms and explain based on Cottrell equation. Lakarkan chronoamperometric excitation dan response waveforms dan terangkan berdasar persamaan Cottrell. (10 marks/markah) 5. (a) Explain the steps involved in the technique below together with an example of the response waveform. Terangkan langkah yang terlibat dalam teknik di bawah bersama dengan contoh response waveform. (15 marks/markah)
SCES2252/SCES2433/06 Cadmium ion is reduced at a DME and the diffusion current measured as 24.3 µa. Previously, a sample of 2.0 X 10-4 mol dm -3 Cd 2+ was analysed at the same DME with the same drop time, and the diffusion current was then found to be 15.2 µa. Calculate the concentration of the sample. (Assume that the residual current was known, and has been subtracted for both samples.) Penurunan ion cadmium pada DME dengan pengukuran diffusion current sebanyak 24.3 µa. Sebelum ini, sampel 2.0 X 10-4 mol dm -3 Cd 2+ telah dianalisis pada DME yang sama dengan masa titik, dan diffusion current adalah 15.2 µa. Hitungkan kepekatan sampel. (mengambil kira residual current diketahui, dan telah ditolak untuk kedua-dua sampel.) (10 marks/markah)
END TAMAT SCES2252/SCES2433/07