We had a Chemistry lab for buffer system, we used HCl and NAOH. We did a graph ( PH vs ml of HCL and NaOH, we told to estimate the buffer capacity using the graph. How to do this?
Buffer capacity can be defined in a variety of ways; the one I use is, "the mols of strong acid or strong base that can be added to 1 L of a buffer that will change the pH by 1 unit. You look at your graph and read the beginning pH and mols (say acid) then find the pH that is 1 unit higher and read mols HCl there. The difference in mols in the buffer capacity. Although we dn't normally think of strong acids or strong bases as buffers, they are buffers in reagions NOT near the equivalence point.
Thanks, you mean finding n for acid or base? The graph represent only PH and volume we added for acid or base in ml.
To estimate the buffer capacity using the pH vs. mL of HCl and NaOH graph, you need to locate the region of the graph where there is a minimal change in pH despite the addition of acid (HCl) or base (NaOH). This region represents the buffer range, where the buffer system is maintaining a relatively stable pH.
Here are the steps to estimate the buffer capacity:
1. Identify the buffer range: Look for a section of the graph where there is a horizontal line or a relatively small change in pH despite the addition of acid (HCl) or base (NaOH). It indicates that the buffer system is effective in resisting changes in pH.
2. Determine the pH range: Note the pH values corresponding to the buffer range on the graph. These will represent the lower and upper limits of the buffer capacity.
3. Calculate the buffer capacity: The buffer capacity can be calculated using the following formula:
Buffer Capacity = Δ(moles of added acid or base) / ΔpH
- Determine the change in moles of acid or base: From the graph, measure the change in volume (mL) of HCl or NaOH added within the buffer range.
- Determine the change in pH: Measure the difference in pH between the lower and upper limits of the buffer range.
4. Divide the change in moles of acid or base by the change in pH. The resulting value will give an approximate measure of the buffer capacity, which represents the amount of acid or base that can be added without causing a significant change in pH within the buffer range.
Remember, the buffer capacity depends on the concentration and ratio of the components in the buffer system. Higher concentrations of the buffer components will result in greater buffer capacity.