In case of a standard hydrogen electrode
- A.absolute electrode potential is not zero
- B.absolute electrode potential is zero
- C.both absolute and standard electrode potential values are zero
- D.electrode potential is zero only at 25 °C
Correct answer
Explanation
The correct answer is A, absolute electrode potential is not zero. The standard hydrogen electrode has a real, non-zero potential; it is only assigned the value zero by convention.
The absolute potential of a single electrode cannot be measured, because any measurement needs a second electrode to complete the circuit. Chemists therefore chose the standard hydrogen electrode, platinum black dipped in an acid of unit hydrogen-ion activity with hydrogen gas at 1 bar, as the reference and fixed its standard potential at 0.00 V at all temperatures. Every other standard electrode potential, such as +0.34 V for copper or -0.76 V for zinc, is measured against it.
B is wrong because the absolute potential is not zero; the zero is an agreed reference value. C is wrong because only the standard (relative) potential is taken as zero, not the absolute one. D is wrong because the zero value is assigned at every temperature, not only at 25 °C.
Exam tip: SHE: E° = 0 V by convention, at all temperatures; its absolute potential is non-zero and cannot be measured alone.
Practice Questions
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- C.ovary, no ovule required
- D.ovule, no ovary required
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