SS2 Third Term Chemistry Lesson Note – Electrolysis

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WEEK 5

TOPIC: ELECTROLYSIS

CONTENT:

1. Faraday’s law of electrolysis.
2. Calculations based on faraday’s laws of electrolysis
3. Uses of electrolysis and corrosion of metals: corrosion treated as a redox process
4. Rusting of iron and its economic costs, prevention of rusting of iron
5. Period 1: faraday’s laws of electrolysis
6. Faraday’s first law of electrolysis states that the mass (m) of a substance librated or deposited at an electrode during electrolysis is directly proportional to the quantity (q) of electricity passing through the electrolyte.

Mathematically;

M α Q ————– (1)

The unit of quantity is coulombs (c). It is the product of current in Amperes and time in seconds

Q = It ——————— (2)

M α It

.: M = k It ——————— (3)

Where k = proportionality constant

I = current in ampere (A)

T = time in seconds (S)

It can be shown that the reciprocal of k, which is called charge –to-mass ratio, is Cf/M. It is constant for a particular element

i.e.  = m = MIt/cF

Re-arranging     = {m/M = It/cF}

Where m= mass f element deposited in grams

M = molar mass of the element in g/mol

I = current, in ampere

t = time, in seconds

c = charge on the element (number of Faradays)

F = Faraday (96500Cmol^-1)

The quantity of electricity required for the passage of one mole of electrons is 96500coulombs.It is called one Faraday. i.e., Faraday, F=96500C = 1 mole of electrons 6.02xelectrons

Faraday’s second law of electrolysis states that when the same quantity of electricity is passed through different electrolytes the relative amounts in moles of the element deposited are inversely proportional to the charge on the ion of respective element.

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