Calculate the change in pH when 9.00 mL of 0.100 M HCl(aq) is added to 100.0 mL of a buffer solution that is 0.100 M in NH3(aq) and 0.100 M in NH4Cl(aq).
Calculate the change in pH when 9.00 mL of 0.100 M NaOH(aq) is added to the original buffer solution.
To calculate the change in pH when HCl is added to the buffer solution, we need to consider the reaction between HCl and the weak base NH3.
Step 1: Write the balanced chemical equation for the reaction between HCl and NH3.
HCl(aq) + NH3(aq) ⇌ NH4Cl(aq)
Step 2: Calculate the initial moles of NH3 and NH4Cl in the buffer solution.
Initial moles of NH3 = (volume of NH3 solution in liters) x (molarity of NH3)
= (0.100 L) x (0.100 M)
= 0.0100 moles NH3
Initial moles of NH4Cl = (volume of NH4Cl solution in liters) x (molarity of NH4Cl)
= (0.100 L) x (0.100 M)
= 0.0100 moles NH4Cl
Step 3: Calculate the moles of NH3 and NH4Cl remaining after the addition of HCl.
Final moles of NH3 = initial moles of NH3 - moles of HCl
= 0.0100 moles NH3 - (9.00 mL) x (0.100 M) x (0.001 L/mL)
= 0.0100 - 0.000900
= 0.00910 moles NH3
Final moles of NH4Cl = initial moles of NH4Cl + moles of HCl
= 0.0100 moles NH4Cl + (9.00 mL) x (0.100 M) x (0.001 L/mL)
= 0.0100 + 0.000900
= 0.0109 moles NH4Cl
Step 4: Calculate the new concentrations of NH3 and NH4Cl.
New concentration of NH3 = (final moles of NH3) / (total volume of the solution)
= 0.00910 moles / (0.109 L)
= 0.0837 M NH3
New concentration of NH4Cl = (final moles of NH4Cl) / (total volume of the solution)
= 0.0109 moles / (0.109 L)
= 0.100 M NH4Cl
Step 5: Calculate the change in pH using the Henderson-Hasselbalch equation.
pH = pKa + log ([A-] / [HA])
The pKa of NH4Cl is approximately 9.26 (from reference sources).
pH = 9.26 + log (0.0837 / 0.100)
= 9.26 + log (0.837)
= 9.26 - 0.0774
= 9.18
So the change in pH when 9.00 mL of 0.100 M HCl is added to the buffer solution is -0.08.
To calculate the change in pH when NaOH is added to the buffer solution, we need to consider the reaction between NaOH and the weak acid NH4+.
Step 1: Write the balanced chemical equation for the reaction between NaOH and NH4+.
NaOH(aq) + NH4Cl(aq) ⇌ NH3(aq) + H2O(l) + NaCl(aq)
Step 2: Calculate the initial moles of NH3 and NH4Cl in the buffer solution (same as previous calculation).
Initial moles of NH3 = 0.0100 moles NH3
Initial moles of NH4Cl = 0.0100 moles NH4Cl
Step 3: Calculate the moles of NH3 and NH4Cl remaining after the addition of NaOH.
Final moles of NH3 = initial moles of NH3 + moles of NaOH
= 0.0100 moles NH3 + (9.00 mL) x (0.100 M) x (0.001 L/mL)
= 0.0100 + 0.000900
= 0.0109 moles NH3
Final moles of NH4Cl = initial moles of NH4Cl - moles of NaOH
= 0.0100 moles NH4Cl - (9.00 mL) x (0.100 M) x (0.001 L/mL)
= 0.0100 - 0.000900
= 0.00910 moles NH4Cl
Step 4: Calculate the new concentrations of NH3 and NH4Cl (same as previous calculation).
New concentration of NH3 = 0.0837 M NH3
New concentration of NH4Cl = 0.099 M NH4Cl
Step 5: Calculate the change in pH using the Henderson-Hasselbalch equation (same as previous calculation).
pH = 9.26 + log (0.0837 / 0.100)
= 9.26 + log (0.837)
= 9.26 - 0.0774
= 9.18
So the change in pH when 9.00 mL of 0.100 M NaOH is added to the buffer solution is -0.08.
To calculate the change in pH when an acid or a base is added to a buffer solution, you can follow these steps:
Step 1: Determine the initial concentrations of the components in the buffer solution before any acid or base is added.
In this case, the initial concentrations are:
[HCl] = 0.100 M (acid)
[NH3] = 0.100 M (base)
[NH4Cl] = 0.100 M (salt)
Step 2: Calculate the moles of acid and base added.
Because the volumes of the solutions are given, you need to convert them to moles using the equation:
moles = (concentration in M) x (volume in L)
For HCl addition:
moles of HCl added = (0.100 M) x (9.00 mL / 1000 mL/L)
For NaOH addition:
moles of NaOH added = (0.100 M) x (9.00 mL / 1000 mL/L)
Step 3: Calculate the moles of the acid and base initially present in the buffer.
moles of NH3 initially = (0.100 M) x (100.0 mL / 1000 mL/L)
moles of NH4Cl initially = (0.100 M) x (100.0 mL / 1000 mL/L)
Step 4: Determine the change in moles for each component.
For HCl addition:
change in moles of NH3 = 0
change in moles of NH4Cl = 0
For NaOH addition:
change in moles of NH3 = 0
change in moles of NH4Cl = 0
Note: Since NH3 and NH4Cl are not reacting with the added NaOH, there is no change in their moles.
change in moles of HCl = moles of HCl added
Step 5: Calculate the new moles of each component in the buffer solution.
moles of NH3 = moles of NH3 initially + change in moles of NH3
moles of NH4Cl = moles of NH4Cl initially + change in moles of NH4Cl
moles of HCl = moles of HCl initially + change in moles of HCl
Step 6: Calculate the new concentrations of each component in the buffer solution.
new [NH3] = moles of NH3 / (total volume in L)
new [NH4Cl] = moles of NH4Cl / (total volume in L)
new [HCl] = moles of HCl / (total volume in L)
Step 7: Calculate the new pH of the buffer solution using the Henderson-Hasselbalch equation.
pH = pKa + log10([base] / [acid])
In this case, the pKa of the NH3/NH4Cl buffer system would be needed to calculate the pH. If not provided, you can assume the pKa to be 9.25, which is the pKa for the ammonium ion NH4+.
new pH = pKa + log10(new [NH3] / new [NH4Cl])
Repeat steps 2 to 7 for both the HCl and NaOH additions to find the respective changes in pH values.
pOH = pKb + log [NH4+]/ [NH3]
pKb of ammonia = 4.74
initial pOH = 4.74 + log 0.100/0.100 = 4.74
pH = 14 - 4.74=9.26
moles NH4+ = moles NH3 = 0.100 L x 0.100 M = 0.0100
moles H+ added = 3.00 x 10^-3 L x 0.100 M=0.000300
NH3 + H+ = NH4+
moles NH3 = 0.0100 - 0.000300=0.00970
moles NH4+ = 0.0100 + 0.000300=0.0103
pOH = 4.74 + log 0.0103/ 0.00970= 4.77
oH = 14 - 4.77 = 9.23
delta pH = 9.26 - 9.23 =0.03
adding OH- the reaction is
NH4+ + OH- = NH3 + H2O
the moles of NH4+ will decrease and the moles of NH3 will increase
I can not answer your second question because thr molar concentration of NaOH is not given