Nicotine is not only bad for you (ahem!), but it also acts as a base in aqueous solution:
Kb = 7x10-7 at 298K.
i) Find G per mol of nicotine acting as a base in aqueous solution at 298K.
ii) Find the pH of the solution if the initial [nicotine] = 0.80 M.
iii) Without doing the calculation, explain how you would find Kb and G at body temperature (310K). Be sure to note what other thermodynamic data you would need to do the calculations.
Tillie, Merissa, Ben -- please don't change names when you're posting on this forum.
i) Isn't delta G = -RTlnK?
ii)If we denote nicotine by N, then
N ==>NOH+ + H^+
Set up Kb expression.
(H^+) = y
(NOH) = y
(N) = 0.8-y
Solve for y
To find the answers to these questions, we will need to understand the concepts of thermodynamics and equilibrium constants. Let's address each question one by one.
i) To find ΔG per mole of nicotine acting as a base in aqueous solution at 298K, we can use the equation:
ΔG = -RTln(Kb)
where ΔG is the Gibbs free energy change, R is the gas constant (8.314 J/mol·K), T is the temperature in Kelvin (298K in this case), and ln is the natural logarithm.
By substituting the given value of Kb (7x10^-7) into the equation, we can calculate the ΔG value.
ii) To find the pH of the solution if the initial [nicotine] is 0.80 M, we can use the fact that nicotine acts as a weak base and undergoes hydrolysis in water:
C6H5CH3N + H2O ⇌ C6H5CH3NH2+ + OH-
The equilibrium constant Kb relates to the concentration of OH- ions produced. The OH- concentration can be determined using the Kb expression:
Kb = [C6H5CH3NH2+][OH-]/[C6H5CH3N]
We are given the initial concentration of nicotine, so we need to determine the equilibrium concentrations of nicotine and its conjugate acid C6H5CH3NH2+ to find the concentration of OH-. Once we have the OH- concentration, we can calculate the pOH and then convert it to pH using the equation pH + pOH = 14.
iii) To find Kb and ΔG at body temperature (310K), you would need to obtain the value of Kb at that temperature. Unfortunately, given only the Kb value at 298K, we cannot directly determine the Kb at 310K.
However, you could potentially use other thermodynamic data like enthalpy (ΔH) and entropy (ΔS) changes to calculate the ΔG at 310K. If you have the values for ΔH and ΔS, you can use the equation:
ΔG = ΔH - TΔS
where T is the temperature in Kelvin (310K in this case). If you have these values, you can substitute them into the equation to find ΔG at 310K.