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Transcript
256
*5.
Ans.
Describe the following types of electrodes giving one example, with reference to formulation,
electrode reaction and Nernst equation for electrode potential.
(a) metal-sparingly salt electrode, (b) gas electrode.
Refer 4.5 (e).
6.
Ans.
What is reference electrode? Give one example.
Refer 4.6
7.
Ans.
Describe the construction and working of Standard Hydrogen Electrode.
Refer 4.6 (a)
8.
Ans.
Describe the construction and working of Calomel Electrode.
Refer 4.6 (b)
9.
Ans.
Why is anode in galvanic cell considered to be negative and cathode positive electrode?
Negative polarity :
(a) According to latest IUPAC convention, the electrode where de-electronation or oxidation
takes place is called anode, for example zinc electrode, Zn(s) ⎯⎯
→ Zn 2+ (aq) + 2e –
(b) The electrons, thus produced are accumulated on the electrode hence, it acquires negative
charge. Due to above reasons the anode in galvanic cell in considered to be negative.
Positive polarity :
(c) According to latest IUPAC convention, the electrode where electronation or reduction
takes place is called cathode, for example copper electrode,
Cu 2+ (aq) + 2e – ⎯⎯
→ Cu(s)
(d) Here, electrons are removed from the electrode and Cu2+(aq) ions are deposited on the
electrode, hence, it acquires positive charge. Due to above reason the cathode in galvanic
cell is considered to be positive.
4.7
ELECTROCHEMICAL SERIES (ELECTROMOTIVE SERIES)
Concept Explanation :
1.
2.
3.
4.
5.
Definition : A series (table) of the arrangement of electrodes (metal or non-metals
in contact with their ions) with the electrode half reactions in decreasing order of
standard potentials, is called electrochemical series. OR A series in which electrodes
or half-cells of elements are arranged in the decreasing order of their standard
reduction potential, is called electrochemical series.
The E0 value is a measure of the tendency of the species to be reduced.
The greater E0 value means greater tendency of the species to accept electrons and undergo
reduction.
The positive E0 values show the tendency of half reactions to occur in the forward direction.
The negative E0 values indicate the tendency of the half reactions to occur in the reverse
direction.
Unique Solutions ®
S.Y.J.C. Science - Chemistry - Part I