Final answer:
To prepare a 0.05 M tris buffer at pH 7.8, first calculate the mass of tris required and then add 6 M HCl gradually until reaching the desired pH.
Step-by-step explanation:
To calculate the amount of tris needed to make a 0.05 M solution with a pH of 7.8, we use the tris pKa which is 8.1, and apply the Henderson-Hasselbalch equation. The equation is pH = pKa + log([base]/[acid]). Given that we need a pH of 7.8, we rearrange the equation to solve for the [base]/[acid] ratio, which gives us the ratio of the concentrations of tris (the base) and trisHCl (the acid).
To make 1.2 liters of the 0.05 M tris buffer, you would first calculate the grams of tris required using the molarity equation: Molarity (M) = moles of solute/liters of solution. That means you need (0.05 moles/liter) * (1.2 liters) = 0.06 moles of tris. Since the molar mass of tris is 121 g/mol, the mass of tris needed is (0.06 moles) * (121 g/mol) = 7.26 grams.
To adjust the pH to 7.8, you would add 6 M HCl until the desired pH is reached. The precise volume depends on the starting pH of the tris solution and how much tris has dissolved. By using a pH meter and titration, you can add 6 M HCl carefully until the pH of the solution is 7.8.