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Laws of electrolysis
Faraday’s laws of electrolysis.
Laws of electrolysis were first stated by Faraday.
According to his laws, the amount of substance produced or dissolved on the electrode during electrolysis depends on.
It states that mass of the substances deposited or dissolved is directly proportional to the quantity of electricity passed. This can be illustrated by the graph below.
Quantity of electricity (Q) = Current × time
Units (coulombs) (amperes) sec
: Coulombs = Amps × Sec
Is the quantity of electricity required to deposit one mole of a mono valet element (Valence of 1 like silver?)
1 mole of silver ions requires faradays (1 mole of electrons to discharge at the cathode).
IF ≡ Ie ≡ 96500C (faradays constant)
2e ≡ 2F ≡ 2 × 96500c
2e≡ 2F ≡ 193000c
2e ≡ 2F ≡ 2× 96,500C
Using graphite electrode
Quantity electricity used.
Q = current (amps) × time /sec.
Q = 0.45 × 10
Q= 4.5 C
The mass of copper deposited.
Cu 2+ (aq) + 2e Cu[c]
2e ≡ 2f ≡ 2 x 96500C
2 × 96500C deposit 64g of copper metal.
2H+ + 2e H2 [g]
4 OH– [aq] 2H2O [L] + O2 [g] + 4e
Calculate the quantity of electricity
1 minute = 60 sec
10 minutes = 10 × 60
= 600 sec
Q = c × t
= 8 × 600
Volume of hydrogen dissolved at (molar gas volume at s.t. p is 22.4 dm 3) or litres)
Calculate the mass of aluminium deposited when a current of 960 amps passes through a solution of Aluminium (iii) oxide in fused crystals for 10 seconds.
2.Faraday’s second law:
The moles of a substance deposited at the electrode in inversely proportional to the charge of the electrode
One moles of a substance deposited at the electrode in inversely proportional to the charge of the electrode
It states that when the same quantity of electricity is passed through solutions of different electrolytes, the relative numbers of moles of the elements deposited are inversely proportional to the charges on the ions of each of the elements respectively.
The masses of different elements liberated by the same quantity of electricity from simple whole ratios when divided by their Relative Atomic mass
During an electrolysis experiments, 0.6g of silver metal and 0.18g of copper metal where deposited by passage of the same quantity of electricity.
RATES OF CHEMICAL REACTIONS
Rates of reaction: Is the degree of reduction in the concentration of the reactants by unit time.
It’s the note at which reactants disappear with time.
Rate at which one of the products accumulates with time
Some reactions produce at a very fast rate and their rate cannot be measured e.g.
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