A chemist titrates of a pyridine solution with solution at . Calculate the pH at equivalence. The of pyridine is . Round your answer to decimal places.

pH = 2.96

Note: The question is incomplete. the complete question is given below:

A chemist titrates 80.0mL of a 0.3184M pyridine C5H5N solution with 0.5397M HBr solution at 25°C . Calculate the pH at equivalence. The pKb of pyridine is 8.77 . Round your answer to 2 decimal places. Note for advanced students: you may assume the total volume of the solution equals the initial volume plus the volume of HBr solution added.

Explanation:

Equation of reaction: C₅H₅NH + HBr > C₅H₅NH⁺ + Br⁻

pKb = -log Kb

8.77= -log Kb

Kb = 1.698 * 10⁻⁹

Volume, V of HBR added to attain equivalence point is obtained:

millimoles of C₅H₅N reacting = 0.3184 M * 80.0 mL  = 25.472 mmol

moles of C₅H₅N = moles of HBr

25.472 mmol = 0.5397 M * V

V = 47.2 mL

25.472 millimoles of both  C₅H₅N and HBr to form C₅H₅NH⁺ and H₂O

C₅H₅NH⁺ formed = 25.472 mmol

Volume of Solution = (80 + 47.2) mL  = 127.2 mL

Concentration of C₅H₅NH⁺, C = 25.472 mmol/127.2 mL = 0.200 M

Ka of C₅H₅NH⁺ = Kw/Kb

Ka = 1.0 * 10⁻¹⁴ /1.698 * 10⁻⁹ = 5.889 * 10⁻⁹

Hydrolysis of C₅H₅NH⁺: C₅H₅NH⁺     +   H₂O >  C₅H₅N  +   H⁺

Initial concentration:          0.200                               0         0

Change in concentration: 0.200 - x                           x         x

Ka = [H⁺][C₅H₅N]/[C₅H₅NH⁺]

Ka = x * x/(c-x)

Assuming x is negligible compared to, the expression above simplifies to

Ka = x²/(c)

x = √(Ka * c)

x = √(5.889 * 10⁻⁶ * 0.200)

x = 1.085 * 10⁻³

Since x = [H+]

[H+] =

Using pH = -log [H+]

pH = -log (1.085 * 10⁻³)

pH = 2.96

i do not get it   at all

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.