Question

For the cell shown, the measured cell potential (Ecell) is -0.3625 V at 25°C with the following half-reaction: Pt(s) | H2(g) | H+(aq). What is the concentration of H+ ions?

A) 0.3625 M
B) 0.723 M
C) 0.18125 M
D) 1.445 M

Answer 1

The concentration of H+ ions is approximately 0.18125 M, determined by taking the antilog of the negative measured cell potential in the Nernst equation at 25°C. Hence the correct option is c.

The Nernst equation is employed to relate the measured cell potential (E cell) of an electrochemical cell to the standard cell potential (E∘cell) and the concentrations of the ions involved. The equation is given by:

`E_c_e_l_l=E^0_c_e_l_l-Rt/nf ln(Q/Q^0)`

Here, R is the gas constant (8.314 J/(mol·K)), T is the temperature in Kelvin, n is the number of moles of electrons exchanged in the reaction, F is Faraday's constant (96,485 C/mol), Q is the reaction quotient, and Q∘ is the equilibrium constant.

For the given half-reaction Pt(s)∣H_2​ (g)∣H +(aq), the reaction quotient Q is determined by the concentration of H+ ions. At 25°C, the antilogarithm of the negative measured cell potential (E cell​ ) provides the ratio of the actual concentration of H+ ions to their standard concentration. In this case, the concentration of H+ ions is approximately 0.18125 M, corresponding to the antilogarithm of -0.3625 V. Therefore, the correct answer is option C. Hence the correct option is c.