ELECTROLYSIS: H20 AND H202 Submttled by: William H Eberhardt, Georgia Institute of Technology, .\tlanta Checked 11.y: David B lIoss, Hiram College, Hila111 Ohm
PREPARATION
Obtain two Hoffman electrolysis outfits, dc source, 3% HsOs, 0.5 M HzSOd. DEMONSTRATION
The concurrent electrolysis of HsO and H202. Fill one electrolysis apparatus with a n~ixtureof water and H?S04and the other with a similar concentration of 3y0 Hz02and H2S04, Connect the electrolysis uuits in series and pass about 1 amp through the circuit. Allow the current to flow a short time before closing the stopcocks to start the demonstration. As electrolysis proceeds, observe the relative volun~esof gases in the four tubes. REMARKS
Water decomposes into 2 voluines of HSand 1 volun~e of 0%.During the early stage, H20syields 2 volumes of O2and somer?hat less than 1volun~eof H?. As theaction
CONCERNING EQUILIBRIUM, FREE ENERGY CHANGES, LE CHATELIER'S PRINCIPLE I1
continues, the volumes of the first three gases remain in the same ratio with considerably less Hz being produced from the H202 The values for vater are normal. The HzOSprov~desa volume of OS equal to that of H2 from HsO which may be expected on the basis of the following aiiodr reaction H20s= O2+ 2H+ 2e-
+
It is not apparent why the volume of Hza t the cathode is quite small, Presumably most of the current is used to reduce H208 to H20, Current efficiency may he brought in here. The value of the faraday may be obtained from the electrolysis of water, This will necessiate maintaining a steady current of about 1 amp, clocking the electrolysis, and making an accurate measuren~entof the volume, temperature, and pressure of the gases.
( m m
Submitted by: William H. Eherhardt, Georgia Institute of Terhnology, Atlanta Checked by: David B Moss, Hiram College, Hiran], Ohio
PREPARATION
Obtain two 600.n11 beakers, two 500-in1 Erlei~n~eyer flasks, hot plate, absolute ethanol, HCI (conc ), CoCL DEMONSTRATION
In one beaker dissolve 10 g of CoCl2 in 500 1111 of ethanol aud 10 the other, 10 g of CoC12in 500 ml of water, Kote the colorsof the solutions. (The blue color is supposedly due to tetrahedrally coordinated Co++ and the pmk to sixfold coordmated Go++.) Slowly add just enough rvater to the blueethanol solutiou to change the color to pink. Divide this pink solution into two equal volumes in the Erlenn~eyerflasks Add conc HCl to one until the blue color reappears, Heat the othe~portion of pink solution on the hot plate until it t ~ ~ rblue n s again.
The hot solnt~oi~ may h? cooled in ao ice bath to restore the pink color. REMARKS
Thc cquilihriuni under study can be discussed in terms of the equatlon CoCL- + 6H30z+ Co(H?OY++ 4ClThe free energy of the reaction nlay be related to the canaton AG = AG" + RT ln[C0(H~0)~++1 + 4RT In [Cl-1 - RT ln [CoCls-I- 6RY ln[H?O] On the basis of this relation, consider the changes iu free energy caused by adding (a) H 2 0 and ( b ) GI-. From experiniental results deduce that AH < 0.
