Experiment 20 CALCULATIONS Name: Instructor: Student ID# Section: Date 20.2 Mole

Question

Experiment 20 CALCULATIONS Name: Instructor: Student ID# Section: Date 20.2 Moles of H, formed, electrons transferred, and copper TABLE TABLE 20.2 TAoxidized during electrolysis of H SO, using copper electrodes. otential for Cu" (aq) + 2 e-Cu(s) assuming Reduction p A | E.=-0.76 V for Zn2+ (aq)+ 2 e, Zrn(s) Reduction potential for sn"(aq) + 2-Sn (s) Reduction potent uction potential for Me'. (aq) + 2 e Mg(s) Total volume of H collected (mlL) (add uncalibrated volume if buret B used) used) Pressure equivalent of height of solution above that in beaker (mmHg) Total pressure of dry H, (mmHg) Moles of H2 formed during electrolysis (mol) Moles of electrons transferred during electrolysis based on H reduced (mol) Average amperage during the electrolysis (A) Number of Faradays of electrons used during electrolysis based on time of electrolysis (F) Mass of copper oxidized during electrolysis (g) Moles of copper oxidized (mol) Moles of electrons transferred during electrolysis based on copper oxidized (mol) Oxidation state of copper ions formed in solution Balanced chemical equation for overll electrolysis reaction Balanced chemical equation for overall electrolysis reaction

Explanation / Answer

A: Reduction potential for Cu2+(aq) + 2e- ------>Cu(s) ; E0(red) = 0.337 V

Reduction potential for Sn2+(aq) + 2e- ------> Sn(s) ; E0(red) = - 0.13 V

Reduction potential for Mg2+(aq) + 2e- ------>Mg(s) ; E0(red) = - 2.37 V

B: Total volume of H2 collected = 33 mL + 0 mL = 33 mL

Pressure equivalent of height of the solution above that in the beaker = 24.5 mm Hg

Total pressure of dry H2 = 24.5 mm Hg

moles of H2 formed during electrolysis = PV/RT = (0.032237 atm x 0.033 L) / (0.0821 L.atm.mol-1K-1x297 K)

= 4.363 x 10-5 mol

2 moles of electron are required to form 1 mol of H2

2H+ + 2e- ---- > H2(g)

Hence moles of electrons transferred during electrolysis based on H+ reduced

= 2x4.363 x 10-5 mol = 8.726x 10-5 mol

Average amperage during electrolysis = (7.3 + 7.2) / 2 = 7.25 A

time, t = 5 min 19 s = 319 s

Q = Ixt = 7.25 x 319 = 2313 Q

Number of Faraday's of electrons required during electrolysis = 2313 Q / 96500 Q/F = 0.0240 F

mass of copper oxidised during electrolysis = 0.3143 g - 0.271 g = 0.0433 g

moles of copper oxidized = mass / atomic mass of Cu = 0.0433 g / 63.55 g/mol = 6.81x10-4  mol

1 mole of copper gives 2 mol electron.

Hence moles of electrons transformed during electrolysis based on copper oxidised

= 6.81x10-4  mol x 2 = 1.36x10-3 mol

oxidationstate of copper ions formed in solution = + 2

Balanced chemical reaction for the overall electrolysis reaction

Cu(s) + 2H+(aq) ------- > Cu2+(aq) + H2(g)

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