Ethanethiol (CH3CH2SH, pKa=10.6) was named the smelliest substance in existence. Draw the equilibrium that forms when ethanethiol is added to a solution buffered at pH 9, and show the relative proportions of all organic species.

To draw the equilibrium that forms when ethanethiol (CH3CH2SH) is added to a solution buffered at pH 9 and show the relative proportions of all organic species, we need to understand how ethanethiol behaves in different pH environments.

First, let's start by understanding the different forms of ethanethiol at different pH levels. Ethanethiol is a weak acid, which means it can donate a proton (H+) to form its conjugate base.

In this case, the protonated form of ethanethiol (CH3CH2SH) is the predominant species in an acidic solution, whereas the deprotonated form (CH3CH2S-) is favored in basic or alkaline solutions.

Given that the solution is buffered at pH 9, we can assume that the buffer system is capable of maintaining the pH at this level. Therefore, the buffer system will consist of a weak acid and its conjugate base. In this case, let's assume the buffer system consists of acetic acid (CH3COOH) and its conjugate base, acetate (CH3COO-).

Now, let's draw the equilibrium using chemical equations:

CH3CH2SH ⇌ CH3CH2S- + H+

This equation represents the equilibrium between the protonated form of ethanethiol and its deprotonated form in the buffer solution at pH 9.

In a buffered solution, the pH is determined by the relative concentrations of the weak acid and its conjugate base. Therefore, the relative proportions of the organic species can be determined by the Henderson-Hasselbalch equation:

pH = pKa + log [A-]/[HA]

In this case, [A-] represents the concentration of CH3CH2S-, and [HA] represents the concentration of CH3CH2SH.

Since the pH of the buffered solution is 9, and the pKa of ethanethiol (CH3CH2SH) is 10.6, we can rearrange the Henderson-Hasselbalch equation and solve for the ratio [A-]/[HA]:

9 = 10.6 + log [A-]/[HA]

Simplifying the equation:

-1.6 = log [A-]/[HA]

To determine the relative proportions of the organic species, we need to calculate the antilog (-1.6) of the ratio [A-]/[HA]:

[A-]/[HA] = antilog (-1.6)

By calculating the antilog and simplifying the result, you can determine the relative proportions of the organic species present when ethanethiol is added to the buffered solution at pH 9.

Note: The calculations involving the Henderson-Hasselbalch equation and antilog may require a scientific calculator or appropriate software for accurate results.