Na2SO4 or K2SO4 1. You may want to experiment by adding a drop of pH indicator (

Question

Na2SO4 or K2SO4

1. You may want to experiment by adding a drop of pH indicator (BTB) to a drop of dilute mineral acid and then add another drop to a drop of dilute strong base (NaOH) to verify your possible answers to this question. What is indicated by the color changes of bromothymol blue in the solution surrounding the electrodes?

2. How can the changes in BTB color be helpful in identifying the products formed at the electrodes and help identify the species being reduced and oxidized?

3. A. Write the equation for the redox reaction taking place at the cathode:

B. Write the equation for the redox reaction taking place at the anode:

:(

Explanation / Answer

Analysis with BTB indicator

1. Addition of an acid first and then a base to a solution containing bromothymol blue (BTB) indicator shows color change. The color change shows when the solution pH is acidic : yellow and when the solution pH is basic : blue coloration.

2. Change in BTB color indicated the electrode anode is undergoing oxidation of material and color change at cathode shows reduction is proceeding. The H+ ions are formed or consumed in the process accordingly.

3. A. at the cathode : 2H2O + 2e- --> H2 + 2OH-

B. at the anode : 2H2O --> O2 + 4H+ + 4e-

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