Doing the Electrolysis l. Obtain 2.0 g of solid KI, using a laboratory balance.

Question

Doing the Electrolysis l. Obtain 2.0 g of solid KI, using a laboratory balance. Do not place this solid directly on the pan of the balance as it will corrode the metal. Use a weighing paper to protect the balance. 2. Transfer the solid to a clean 125-mL or 250-mL Erlenmeyer flask. Add 100 ml of distilled water from a graduated cylinder, and swirl until a homogeneous solution is obtained. 3. Measure and record the pH of this solution. When you have an opportunity, calculate and record the hydroxide ion concentration, [OH 4. Place two graphite electrodes in a 150-mL beaker. Clamp the electrodes so that they cannot touch each other. Your laboratory instructor will tell you how to do this if it is not obvious from your eauinment

Explanation / Answer

Lets start with the possibility of products at cathode and anode.

As we know, the cathode is the negative terminal and will attract cations, anode is positive terminal and attract the anions.

If KI is dissolved in water, it dissociates to K+ and I- ions

So possible reactions at the cathode:

(a) K+ + e ------------> K

(b) H2O + e ------------> 1/2 H2 + OH-

Due to E0 values, water will be reduced at the cathode liberating H2

In the anode, possibilities (a) I- ----------> 1/2 I2 + e

(b) H2O ----------------> 1/2 O2 + 2 H+ + 2e

Again due to E0 values I2 will be liberated in the anode

Therefore our observation will be violet colored iodine at the anode and bubbles of Hydrogen at the cathode.

Over all cell reaction anode I- ½I2(s) + e cathode H2O + e 1/2H2 + OH- ------------ ---------------------------------------- Overall I- + H2O 1/2 I2 + 1/2 H2 + OH-

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