how many grams each of tris and tris HCl are needed to make up 500ml of 1m tris buffer with a PH of 8.0.
pka of tris =8.3
mwt of tris =121
mwt of tris HCl =175
how many gramms of trains and tris HCl are needed to make up 500ml of 1m trains buffer with a pH of 8.0?
history and introduction of biochemistry
To calculate the amount of tris and tris HCl needed to make up a 500 ml 1M Tris buffer with a pH of 8.0, we first need to understand the relationship between the pH, pKa, and ratio of the acid (tris) to its conjugate base (tris HCl).
The Henderson-Hasselbalch equation relates the pH and pKa:
pH = pKa + log([A-]/[HA])
Where:
pH = Target pH of the buffer (8.0)
pKa = Acid dissociation constant of the acid (tris in this case) (8.3)
[A-] = Concentration of the conjugate base (tris HCl) in the buffer
[HA] = Concentration of the acid (tris) in the buffer
Using the Henderson-Hasselbalch equation, we can solve for the ratio [A-]/[HA]:
8.0 = 8.3 + log([A-]/[HA])
Simplifying the equation:
-0.3 = log([A-]/[HA])
Taking the antilog of both sides:
10^(-0.3) = [A-]/[HA]
Now we know the ratio of [A-] to [HA]. In a 1M Tris buffer, the sum of [A-] and [HA] is 1. Therefore, we can represent [A-] as x and [HA] as (1 - x), where x represents the fraction of the buffer made up by tris HCl.
10^(-0.3) = [A-]/[HA]
10^(-0.3) = x / (1 - x)
Solving for x:
x = 10^(-0.3) * (1 - x)
Simplifying:
x = 10^(-0.3) - 10^(-0.3) * x
x + 10^(-0.3) * x = 10^(-0.3)
x(1 + 10^(-0.3)) = 10^(-0.3)
x = 10^(-0.3) / (1 + 10^(-0.3))
Now that we have the ratio of [A-] to [HA], we can calculate the grams needed for each component.
For tris HCl:
1M Tris buffer means 1 mole of Tris in 1 liter of solution.
Molecular weight (mwt) of tris HCl = 175 g/mol
Given that we need to make a 500 ml buffer, the number of moles of tris HCl needed is:
mol = 1M x 0.5 L = 0.5 mole
Mass of tris HCl = moles x mwt = 0.5 mol x 175 g/mol
For tris:
The ratio x represents the fraction of the buffer made up by tris HCl. Therefore, the fraction of the buffer made up by tris is (1 - x).
Mass of tris = (1 - x) x 1M x 0.5 L x mwt of tris
Molecular weight (mwt) of tris = 121 g/mol
Now, substituting the value of x:
Mass of tris = (1 - 10^(-0.3) / (1 + 10^(-0.3))) x 1M x 0.5 L x 121 g/mol
Calculate this expression to get the mass of tris needed.
Note: It is important to use precise weighing equipment and proper laboratory techniques when preparing buffers to ensure accuracy and precision.