For this galvanic cell reactions 3HNO_2(aq) + BrO_2 (aq) rightarrow 3H (aq) + 3N

Question

For this galvanic cell reactions 3HNO_2(aq) + BrO_2 (aq) rightarrow 3H (aq) + 3NO_2 (aq) + Br (aq) the Nernst equation that the galvanic cell will have a more negative voltage if your increase the pH. Decrease the Br concentration. Increase the NO_2 concentration Increase the BrO_2 concentration. The oxidation number of carbon changes from___in this redox reaction. 2MaO_4^- (aq) + 3C_2O_4^3 (aq) + 4OH (aq) rightarrow 2MaO_2(s) + 6CO_3^2 (aq) + 2H_2O(f) + 3 to +4 + 3 to + 6 + 4 to + 3 + 6 to + 4 The reaction Zn(s) + Ni^2 (aq) rightarrow Zn^2 (aq) + Ni(s) occurs in the galvanic cell shown. Which statement is true? Electrons flow to the Ni electrode. Na^+ ions flow toward the Zn electrode. Electrons flow to the Ni electrode. Na^+ ions flow toward the Ni electrode. Electrons flow to the Zn electrode. Na^+ ions flow toward the Zn electrode. Electrons flow to the Zn electrode. Na^+ ions flow toward the Ni electrode. Which species is the most powerful reducing a

Explanation / Answer

19 ) according to Nernst equation

Ecell = E0cell - 0.0592 / n log Q

Q= [H+]^3 [[NO3-]^3 [ Br-] / [HNO3]^3 [BrO3-]

So if we increase Q the value of Ecell will decrease

a) increasing pH means we are decreasing [H+] which will decrease Q and hence will increase Ecell (more positive)

b) Decrease Br- means we are increasing Q and hence will decrease Ecell (more negative)

20) Let Oxidation number of carbon in C2O4-2 = x

2x + 4(-2) = -2

x = +3  

Let Oxidation number of carbon in CO3-2 = x

x + 3(-2) = -2

x = +4

so change is +3 to +4

21) Zinc is undergoing oxidation, and gives 2e which will be transfered to Ni+2 to form Ni(s) and Na+ will flow towards Ni electrode

22) The most powerful reducing agent is one with lowest reduction potential

Answer : Na

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