Consider the titrtation of 25.0mL of 0.0100M Sn2+ by 0.0500M Ti3+ in 1 M HCL, using Pt and Saturated Calomel Electrodes to find the endpoint.
F=96486.7 Cmol
E0 Sn4+/Sn2+ =0.15V
E0 TI3+/TI+ = 1.28
Esce = 0.241V
R=8.3141 J K Mol
(a) Write the balanced reaction.
Sn4+ + 2e- <--> Sn2+
TI3+ <--> TI+ + 2e-
Sn2+ + Tl3+- -> Sn4+ + Tl+
(b) Write two different half reactions for the net cell reaction.
I'm assuming this means
Sn4+ + 2e- <--> Sn2+ E0= 0.15V
TI3+ <--> TI+ + 2e- E0= 1.28 V
(c) Write the two nernst equations for the net cell reaction
Prior to the equivalence point, the equation would be;
E=1.28+RT/F ln(TI3+/TI+)-SCE (0.241)
Where TI3+/TI+ = Conc. products/reactants.
After the equivalence point, reaction then becomes,
E=0.15 + RT/F ln(Sn4+/Sn2+) - SCE
(D) calculate E at the following volumes of TI3+ : 1.00mL, 2.50mL, 4.90mL, 5.00mL,5.10mL and 10.0mL
This is the section I am having difficulty with, if anyone could help, thanks.
One problem I had with this yesterday was that the problem quote Ti and all of the answers quote Tl. Not to same so you need to clear up that little typo.
To calculate the potential (E) at the given volumes of TI3+, you will need to use the Nernst equation. The Nernst equation relates the concentration of species involved in an electrochemical reaction to the potential of the cell. The general form of the Nernst equation is:
E = E0 - (RT/nF) * ln(Q)
where:
E is the cell potential
E0 is the standard cell potential
R is the gas constant (8.3141 J K^(-1) mol^(-1))
T is the temperature in Kelvin
n is the number of electrons transferred in the reaction
F is Faraday's constant (96486.7 C mol^(-1))
ln is the natural logarithm
Q is the reaction quotient, which is the ratio of the concentrations of products to the concentrations of reactants, raised to their stoichiometric coefficients.
Given that:
E0 Sn4+/Sn2+ = 0.15 V
E0 TI3+/TI+ = 1.28 V
Esce = 0.241 V
TI3+/TI+ = Concentration of products (TI+)/Concentration of reactants (TI3+)
Sn4+/Sn2+ = Concentration of products (Sn4+)/Concentration of reactants (Sn2+)
You can now calculate the potential (E) at the given volumes of TI3+:
For 1.00 mL of TI3+:
Concentration of Sn4+ = 0
Concentration of Sn2+ = 0.0100 M
Q = (0)/(0.0100) = 0
E = 0.15 - [(8.3141 * T)/(2 * 96486.7)] * ln(0) - 0.241
For 2.50 mL of TI3+:
Concentration of Sn4+ = ? (Unspecified)
Concentration of Sn2+ = ? (Unspecified)
Q = (Concentration of Sn4+)/(?)
You will need to specify the concentrations of Sn4+ and Sn2+ to calculate Q and subsequently the potential (E). Repeat this process for each given volume of TI3+.