what will be the pH change when 20 mL of .1M NaOH is added to 80 mL of a buffer solution consisting of .164M NH3 and .187M NH4Cl? Pka 9.25
Use the Henderson-Hasselbalch equation to obtain the initial pH. I have something like 9.19 but you need to confirm that and do it more accurately than I estimated.
Then work the addition part of the problem.
You started with 80 mL x 0.187 M NH4Cl = 13.12 mmoles.
You started with 80 mL x 0.164 = 14.96 mmoles. Now we add NaOH and I like to use an ICE chart.
........NH4^+ + OH^- ==> NH3 + H2O
initial 14.96....0......13.12......
change..-2.....+2mmoles..+2
final...12.96....0......15.12
Now substitute into the HH equation and solve for the new pH. I think 9.3 is close for the new pH.
To determine the pH change when an acid or base is added to a buffer solution, we need to consider the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
In this case, NH3 acts as the base (A-) and NH4Cl acts as the acid (HA). The pKa value given is 9.25.
Let's calculate the initial pH of the buffer before any NaOH is added:
[A-] = 0.164 M
[HA] = 0.187 M
pH = 9.25 + log (0.164/0.187)
pH = 9.25 + log (0.877) ≈ 9.25 - 0.06 ≈ 9.19
The initial pH of the buffer solution is approximately 9.19.
Now, we will consider the addition of NaOH. We have 20 mL of a 0.1 M NaOH solution.
To determine the change in pH, we need to calculate the moles of NH4+ and NH3, and see how they are affected by the added OH- ions.
First, let's calculate the moles of NH4+ and NH3 in the 80 mL of buffer solution:
Moles of NH4Cl = 0.187 M x 0.080 L = 0.01496 mol
Moles of NH3 = 0.164 M x 0.080 L = 0.01312 mol
Since NaOH is a strong base, it reacts completely with NH4Cl to form NH3 and water:
NH4+ + OH- → NH3 + H2O
Since the reaction is 1:1, 0.01496 mol of NH4+ reacts with 0.01496 mol of OH-, and NH3 is formed.
Moles of NH4+ remaining = 0.01496 mol - 0.01496 mol = 0 mol
Moles of NH3 formed = 0.01312 mol + 0.01496 mol = 0.02808 mol
Now we can calculate the new concentrations of NH4+ and NH3:
[HA] = Moles of NH4+ remaining / Total volume of solution = 0 mol / 0.100 L = 0 M
[A-] = Moles of NH3 formed / Total volume of solution = 0.02808 mol / 0.100 L = 0.2808 M
Using the Henderson-Hasselbalch equation, we can calculate the new pH:
pH = 9.25 + log (0.2808/0)
pH = 9.25 + log (∞) ≈ 9.25 + ∞ ≈ ∞
The pH after adding 20 mL of 0.1 M NaOH is approximately ∞ (Infinity). This indicates that the solution has become more basic.
Therefore, the pH change is from approximately 9.19 (initial pH) to approximately ∞ (final pH).
To determine the pH change when adding NaOH to a buffer solution, we need to calculate the initial and final pH values.
A buffer solution consists of a weak acid and its conjugate base (or a weak base and its conjugate acid), which resist changes in pH when small amounts of acid or base are added.
Here's how we can approach this problem:
Step 1: Calculate the initial pH of the buffer solution
We have the concentration of NH3 and NH4Cl in the buffer solution, as well as the pKa (9.25) of the ammonium ion (NH4+). By using the Henderson-Hasselbalch equation, we can find the initial pH.
pH = pKa + log([A-]/[HA])
[A-] represents the concentration of the conjugate base (NH3) and [HA] represents the concentration of the weak acid (NH4Cl).
Plugging in the values:
pH = 9.25 + log(0.164/0.187)
Step 2: Calculate the concentration of NH3 and NH4Cl after adding NaOH
When 20 mL of 0.1M NaOH is added to the 80 mL buffer solution, it will react with NH4+ to form NH3 and water. This will result in a decrease in the concentration of NH4+ and an increase in NH3 concentration.
To determine the new concentrations, we need to calculate the moles of NH4+ initially present and the moles of NaOH added.
Moles of NH4Cl = concentration of NH4Cl * volume (in liters)
Moles of NaOH = concentration of NaOH * volume (in liters)
Step 3: Calculate the new concentrations of NH3 and NH4Cl
Given that NH4Cl dissociates into NH4+ and Cl-, and 1 mole of NH4Cl produces 1 mole of NH4+:
Concentration of NH4+ = moles of NH4+ initially present - moles of NH4+ reacted with NaOH
Given that NaOH reacts with NH4+ in a 1:1 ratio:
Concentration of NH3 = moles of NH3 initially present + moles of NH4+ reacted with NaOH
Step 4: Calculate the final pH of the buffer solution
Using the Henderson-Hasselbalch equation again with the new concentrations of NH3 and NH4Cl, and the same pKa value of 9.25, we can determine the final pH.
pH = pKa + log([A-]/[HA])
[A-] represents the new concentration of NH3 and [HA] represents the new concentration of NH4Cl.
By subtracting the initial pH from the final pH, you can determine the pH change caused by adding NaOH to the buffer solution.