You have a 135 mL buffer solution of 0.35 M NH3 and 0.40 M NH4+ in concentration.
NH4+ (aq) + H2O (l) <----> H3O+ (aq) +NH3 (aq)
Calculate the pH of this buffer after adding 10.00 mL of 0.095 M NaOH.
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To calculate the pH of the buffer solution after adding NaOH, we need to consider the reaction that occurs between NH3 and NaOH:
NH3 (aq) + NaOH (aq) → NH4+ (aq) + H2O (l)
First, let's calculate the number of moles of NH3 and NH4+ initially present in the buffer solution:
Moles of NH3 = Concentration of NH3 × Volume of NH3 solution
= 0.35 M × 0.135 L
= 0.04725 moles
Moles of NH4+ = Concentration of NH4+ × Volume of NH4+ solution
= 0.40 M × 0.135 L
= 0.054 moles
Since NH3 and NH4+ are initially in a 1:1 ratio, the moles of NH3 and NH4+ are the same.
Now, let's calculate the number of moles of NaOH added:
Moles of NaOH = Concentration of NaOH × Volume of NaOH solution
= 0.095 M × 0.01 L
= 0.00095 moles
Since NH4+ and NaOH react in a 1:1 ratio, the moles of NH4+ decrease by the same amount as the moles of NaOH added. Hence, the new concentration of NH4+ is:
New moles of NH4+ = Initial moles of NH4+ - Moles of NaOH added
= 0.054 moles - 0.00095 moles
= 0.05305 moles
To calculate the new volume of the buffer solution, we need to add the volume of NaOH to the initial volume of the buffer:
New volume of buffer solution = Volume of initial buffer + Volume of NaOH added
= 0.135 L + 0.01 L
= 0.145 L
Now we can calculate the new concentration of NH3:
New concentration of NH3 = Moles of NH3 / New volume of buffer solution
= 0.04725 moles / 0.145 L
= 0.32586 M (rounded to five decimal places)
To find the concentration of H3O+ (which is needed to calculate pH), we can use the equation provided in the question:
NH4+ (aq) + H2O (l) ⇌ H3O+ (aq) + NH3 (aq)
Since NH4+ and NH3 are initially in a 1:1 ratio, their concentrations are the same. Therefore, the concentration of H3O+ is also 0.32586 M.
Now, let's calculate the pH of the buffer solution using the concentration of H3O+:
pH = -log[H3O+]
= -log(0.32586)
= 0.487 (rounded to three decimal places)
Therefore, the pH of the buffer solution after adding 10.00 mL of 0.095 M NaOH is approximately 0.487.