How many moles of HCl must be added to 100mL of a 0.100 M solution of methylamine (pKb=3.36) to give a buffer having a pH of 10.0?

To find out how many moles of HCl need to be added, we need to set up an equation using the Henderson-Hasselbalch equation for the buffer solution:

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

In this equation:
- pH is the desired pH of the buffer, which is 10.0
- pKa is the negative logarithm of the acid dissociation constant of the conjugate acid (methylamine in this case)
- [A-] is the concentration of the conjugate base (methylamine) in the buffer solution
- [HA] is the concentration of the acid (methylamine) in the buffer solution

First, let's determine the concentration of methylamine in the buffer solution. Since we have a 0.100 M solution of methylamine, the concentration of [HA] is 0.100 M.

Next, we need to find the concentration of the conjugate base [A-] in the buffer solution. To do that, we can use the pKb value and the following equation:

pKb = pKa + log ([A-]/[HA])

Let's rearrange the equation to solve for [A-]:

[A-]/[HA] = 10^(pKb - pKa)

Substituting the given values:

[A-]/0.100 = 10^(3.36 - 14)

[A-]/0.100 = 10^(-10.64)

[A-]/0.100 = 4.525 x 10^(-11)

Next, we need to find the moles of methylamine in the 100 mL solution. To do that, we can use the concentration and the volume:

moles of methylamine = concentration × volume

moles of methylamine = 0.100 M × 0.100 L

moles of methylamine = 0.010 moles

Since the ratio of moles of conjugate base [A-] to [HA] in a buffer solution is 1:1, we need to add an equal number of moles of HCl to convert all the methylamine into its conjugate acid (methylammonium chloride).

Therefore, the number of moles of HCl needed to add is also 0.010 moles.

So, 0.010 moles of HCl must be added to 100 mL of the 0.100 M solution of methylamine to obtain a buffer solution with a pH of 10.0.

explanation please

a) 8.1

.65

Use the Henderson-Hasselbalch equation.