1. With the same initial solution of 0.75 moles formate and 0.85 moles formic acid to make a buffer solution. The Ka of formic acid is 1.8x10-4. You add 8g sodium hydroxide to this solution, what is the new pH?
2. With the same initial solution of 0.75 moles formate and 0.85 moles formic acid to make a buffer solution. The Ka of formic acid is 1.8x10-4. You add 16g hydrobromic acid to this solution, what is the new pH?
Assume a 1L Solution
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To answer these questions, we can use the Henderson-Hasselbalch equation. The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa of the acid and the concentrations of the acid and its conjugate base.
The Henderson-Hasselbalch equation is given as follows:
pH = pKa + log([conjugate base]/[acid])
1. In the first question, we are adding sodium hydroxide (NaOH) to the buffer solution. Sodium hydroxide is a strong base, and when it reacts with the formic acid (HCOOH), it forms sodium formate (HCOONa) and water.
The balanced chemical equation is:
HCOOH + NaOH -> HCOONa + H2O
Since the initial solution contains 0.75 moles of formate and 0.85 moles of formic acid, we need to determine the concentrations. The total volume of the solution is not given, so we cannot calculate the exact concentrations. However, assuming the volume remains constant, we can use the given moles as a ratio.
Let's assume we have 1 L of solution. Since we have 0.75 moles of formate and 0.85 moles of formic acid, the concentrations will be 0.75 M and 0.85 M, respectively.
To calculate the new pH, we need to determine the new concentrations of the acid and its conjugate base after the reaction with NaOH. From the balanced equation, we see that 1 mole of formic acid reacts with 1 mole of sodium hydroxide, forming 1 mole of sodium formate.
Therefore, the moles of remaining formic acid will be 0.85 - 0.85 = 0 moles, and the moles of formate will be 0.75 + 0.85 = 1.6 moles.
Now, using these new concentrations, we can calculate the new pH using the Henderson-Hasselbalch equation.
pH = pKa + log([conjugate base]/[acid])
pH = -log(1.8x10^-4) + log(1.6/0)
pH = -log(1.8x10^-4)
So, the new pH after adding 8 g of sodium hydroxide cannot be determined without additional information about the volume of the solution.
2. In the second question, we are adding hydrobromic acid (HBr) to the buffer solution. Hydrobromic acid is a strong acid, and when it reacts with the formate ion (HCOO-), it forms formic acid (HCOOH) and water.
The balanced chemical equation is:
HCOO- + HBr -> HCOOH + Br-
Again, assuming we have 1 L of solution for ease of calculation, we have 0.75 M of formate and 0.85 M of formic acid.
Since 1 mole of formate reacts with 1 mole of hydrobromic acid, we will consume 0.75 moles of formate and form 0.75 moles of formic acid.
The new concentrations will be 0.85 + 0.75 = 1.6 M of formic acid and 0.75 - 0.75 = 0 M of formate.
Using these new concentrations, we can calculate the new pH using the Henderson-Hasselbalch equation as in the previous example:
pH = pKa + log([conjugate base]/[acid])
pH = -log(1.8x10^-4) + log(0/1.6)
pH = -log(1.8x10^-4/1.6)
Again, without knowing the exact volume of the solution, we cannot determine the new pH.
In summary, without knowing the exact volume of the solution, we cannot calculate the new pH after adding 8 g of sodium hydroxide or 16 g of hydrobromic acid to the buffer solution.