HW_4 - aliquot to 10 32.70mL of the 0.01080MEDTA standard...

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CHEM 150 HOMEWORK #4 Due: Monday, 7/14/08 1. Calculate the standard potential for the reaction ZnCO 3 (s) + 2e - = Zn(s) + CO 3 2- (aq) for ZnCO 3 having K sp = 1.4 X 10 -11 . 2. The following cell was found to have a potential of 0.512V: Pt(s) H 2 (l.00atm) HA (0.200M) ││ SCE Calculate Ka for HA. 3. For the cell, Zn(s ) ZnCO 3 (s) CO 3 2- (aq) ││ SCE Determine pCO 3 if the potential was 0.989V (you will need E° from #1). 4. A 1.728g sample of a Pb/Cd alloy was dissolved in acid and diluted to exactly 500mL. Titration of a 25.00mL aliquot at a pH = l0 in an NH 4 + /NH 3 buffer required 43.60mL of standard 0.01080M EDTA and involved both cations (Pb 2+ and Cd 2+ ). The cadmium ion was then masked by using an HCN/NaCN buffer to bring the pH of a second 25.00mL
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Unformatted text preview: aliquot to 10; 32.70mL of the 0.01080MEDTA standard was used in this titration and involved only the Pb 2+ . Calculate the respective percentages of lead and cadmium in the alloy. 5. Consider the following redox reaction: 2CS(NH 2 ) 2 + 4BrO 3-+ 3H 2 O = 3CO (NH 2 ) 2 + 3SO 4 2-+ 4Br-+ 6H + (a) Identify the atoms which are oxidized and reduced. (b) Determine the number of electrons transferred. (c) Write the balanced half-reactions. 6. The following cell was employed to determine pSO 4 of a solution: SCE ││ Hg 2 SO 4 (sat'd), SO 4 2-(xM) │ Hg Calculate the pSO 4 if the potential was 0.506V....
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