Question

Revised 7/25/19 Station CHM 112 Determination of an Equivalent Mass by Electrolysis Post Lab Ouestions 1. In an electrolysis cell similar to the one employed in this experimenta student observed that his unknown metal anode lost 0.20 while a total volume of 9630 ml of was being produced. The temperature in the laboratory was 25°C and the barometric pressure was 748 mm Hg. At 25°C the vapor pressure of water is 23.8 mm Hg. To find the equivalent mass of his metal he filled in the blanks below Fill in the blanks as he did. PH-Phar-PHO mm Hg VH- ml T- nH2 moles (where P-P ) 1 mole H; requires passage of faraday's No. of faradays passed - Loss of mass of metal anode = No. grams of metal lost per faraday passed = 8=EM The student was told that his metal anode was made of iron. MM Fe = The charge n on the Fe ion is therefore 2. In standard, IUPAC units, the faraday is equal to 96,480 coulombs. A coulomb is the amount of electricity passed when a current or one ampere llows for one second. Given the charge on an electron, 1.6022 x 10-coulombs, calculate a value for Avogadro's number Page 1 of 1

Answer 1

(i) P_H2 = 748 - 23.8 = 724.2 mm Hg = (724.2/760) atm = 0.953 atm

(ii) V_H2 = 96.3 mL = (96.3/1000) l = 0.0963 L

(iii) T = (25+273) K = 298 K

(iv) n_H2 = PV/RT = 0.953 atm * 0.0963 L/(0.0821 L.atm.mol^-1.K^-1 * 298 K) = 0.00375 mol

(v) 1 mole of H2 required passage of 2 Faradays.

(vi) Number of Faradays passed = 0.00375*2 = 0.0075 F

(vii) Loss of mass of metal anode = 0.208 g

(viii) No. of grams of metal lost per Faradays passed = 0.208 g/0.0075 = 27.73

(ix) MM of Fe = 55.456 g

(x) The charge on Fe-ion = +2