Question

CuO reacts with HCl but Cu does not, why?
A.Copper has a higher reduction potential than hydrogen, it does not react with non – oxidising acids like HCl.
B.Copper has a lower reduction potential than hydrogen, it does not react with non – oxidising acids like HCl.
C.Copper is a less reactive metal, hence does not react with any acid
D.Both Cu and CuO do not react with HCl.

Answer 1

Hint: Reduction potential is the tendency of a substance to accept or gain electrons. Only metals which have their standard reduction potentials less than that of hydrogen displace hydrogen from their non – oxidising acids.

Complete step by step answer:
Reduction potential is the measure of the tendency of a chemical species to acquire electrons from an electrode and thus get reduced. Reduction potential is measured in volts (V). Each species has its own intrinsic redox potential, for instance, the more positive the reduction potential, the greater the species' affinity for electrons and tendency to be reduced.
In the given question, CuO reacts with HCl according to the reaction:
$$CuO+2HCl\to CuC{l}_2+H_{2}O$$
But Cu does not react with HCl because the reduction potential of Cu is higher than that of hydrogen. Only metals which have their reduction potential less than that of hydrogen react with non – oxidising acids.
i.e.
$$Cu\to C{u}^{+2}+2e^{-};\mathrm{\Delta }{E}_1$$
$$H\to H^{+}+e^{-};\mathrm{\Delta }{E}_2$$
$$\mathrm{\Delta }{E}_1>\mathrm{\Delta }{E}_2$$
Hence, the reaction is not feasible.
Therefore, the correct answer is (A).

Note: Remember that when we multiply a reaction by a constant, its electrode potential does not change. It can be very well confirmed with the Nernst equation.