4. Calculate the theoretical number of mL of 0.200 M HCl needed to completely ne
ID: 508353 • Letter: 4
Question
4. Calculate the theoretical number of mL of 0.200 M HCl needed to completely neutralizethe weak base in the 25.0 mL of buffer. From your graph, determine how many mL of 0.200 M HCl were actually used to neutralize the base in the buffer. Compare this value to the calculated value. Did your buffer resist change in pH for the entire titration?Explain. Calculate how many moles of acid were added to reach the capacity of thebuffer.
Table 1: Recordings of pH Part D pH WHCD Part C pH Part D pH (w/ NaOH) 2.75 4.27 175 122.16 4.62 4.81 5.04 Figure 1: pH vs Concentration of HCI pH vs Concentration of HCI 15 Volume of HCl Added (mL) Figure 2: pH vs Concentration of NaOH pH vs Concentration of NaOH 12 10 10 20 Volume of NaOH Added (mL)Explanation / Answer
Buffer capacity
The amount of acid or base needed to completely neutralize the base or acid part of the buffer component.
With 25 ml of buffer solution,
theoretical value needed to neutralize bas component of buffer (0.1 M) = 25 ml x 0.1 M/2
= 12.5 ml
Here we have taken equal volumes of base and acid component in the buffer. Assuming molarity of buffer = 0.1 M.
From the first graph,
the volume of 0.2 M HCl needed to neutralize the base component of buffer = 12.5 ml
moles of acid added to reach the buffer capacity = molarity of HCl x volume of HCl added
= 0.2 M x 12.5 ml
= 2.5 mmol
From the second graph,
the volume of NaOH needed to neutralize the acid component of buffer = 16.5 ml
So the amount of acid added matches with the theoretical value for the HCl required to neutralize base component of the buffer.
The buffer gave almost a straight line (with minor slope) till the equivalence point for the titration with HCl and thus, the buffer resisted change in pH throughout the titration range with HCl
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