A buffer is made at pH 7.3. 0.15 M using imidazole And 1 M hydrochloric acid to form the buffer. Can you show calculations for the formation of 500 mls of this buffer?
I looked up the pKa for imidazole as 7.00 but you should confirm that in your text or lecture materials. If we call the base BNH2, then
..........BNH2 + HCl ==> BNH3^+ + Cl^-
initial...0.15....0......0..........0
add HCl............x
equil......0.15-x...0....x.........x
Then pH = pKa + log(base)/(acid)
7.30 = 7.00 + log(0.15-x)/x
Solve for x which will be the M HCl you want. I get something like 0.05M
You want 0.500 L of 0.15 buffer so you want 0.075 moles.
0.075 moles imidazole x molar mass = grams.
You can go from here with the amount of HCl to add.
After you finish the calculation take my advice and work the other way to see if adding the materials in your calculation will give you a pH of 7.30
Isn't imidazole c3h4n2 and not bnh2 though?
Certainly! To calculate the amounts of imidazole and hydrochloric acid needed to prepare 500 ml of a buffer with a pH of 7.3, we need to use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
In this equation, pKa is the dissociation constant of the weak acid, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid.
First, we need to find the pKa value for imidazole. The pKa of imidazole is approximately 7.0, so we'll use that value.
Given:
pH = 7.3
[HA] = 0.15 M
To find [A-], we rearrange the Henderson-Hasselbalch equation:
[A-]/[HA] = 10^(pH - pKa)
[A-]/0.15 = 10^(7.3 - 7.0)
[A-]/0.15 = 10^0.3
[A-]/0.15 = 2
[A-] = 0.15 M * 2
[A-] = 0.30 M
So, to prepare the buffer, we'll need 0.30 M of imidazole and 1 M of hydrochloric acid.
To find the volumes of each solution required, we'll use the formula:
Volume = (Concentration * Volume)/(Concentration)
Let's calculate the volumes needed:
Volume of imidazole = (0.30 M * 500 ml) / 0.15 M
Volume of imidazole = 1 L
Since the concentration of imidazole is 0.30 M, we need 1 liter (or 1000 ml) of imidazole solution.
Volume of hydrochloric acid = (1 M * 500 ml) / 1 M
Volume of hydrochloric acid = 500 ml
So, to prepare 500 ml of this buffer, you'll need 1000 ml (1 liter) of a 0.30 M imidazole solution and 500 ml of 1 M hydrochloric acid.