Calculate the change in PH when 6 ml of 0.1 M HCl is added to 100 ml of a buffer solution that is 0.1 M in NH3 and 0.1 M in NH4Cl. And calculate the change in PH when 6 ml of 0.1 M NaOH is added to the original buffer solution.
See your post above.
6.75
To calculate the change in pH, we need to consider the effect of the added acids or bases on the concentrations of the acidic and basic components of the buffer solution.
1. Change in pH when HCl is added:
First, we need to determine the initial concentrations of NH3 and NH4Cl in the buffer solution. Since they are both 0.1 M, the concentration of NH3 is also 0.1 M, and the concentration of NH4Cl is also 0.1 M.
When HCl is added, it reacts with NH3 according to the following equation:
HCl + NH3 → NH4Cl
Since the concentration of HCl is 0.1 M and the volume added is 6 ml (0.006 L), we can calculate the number of moles of HCl added:
moles of HCl = concentration x volume = 0.1 M x 0.006 L
Since HCl reacts with NH3 in a 1:1 ratio, the same number of moles of NH3 will be converted to NH4Cl. Therefore, the concentration of NH3 will decrease by the number of moles of HCl added.
To calculate the new concentration of NH3, we divide the moles of NH3 by the total volume of the buffer solution:
new concentration of NH3 = (initial concentration of NH3 x initial volume of NH3) / total volume of buffer solution
The total volume of the buffer solution is the sum of the volumes of NH3 and NH4Cl (100 ml + 6 ml = 106 ml), which can be converted to liters (0.106 L).
Now that we have the new concentration of NH3, we can calculate the new concentration of NH4Cl by subtracting it from the initial concentration of NH3:
new concentration of NH4Cl = initial concentration of NH4Cl + initial concentration of NH3 - new concentration of NH3
Finally, we can determine the change in pH using the Henderson-Hasselbalch equation:
pH = pKa + log10([A-] / [HA])
In this case, NH4Cl is the acidic component (HA) and NH3 is the basic component (A-). The pKa is the dissociation constant of NH4Cl, which is 9.25 at 25°C.
2. Change in pH when NaOH is added:
Similar to the previous steps, we need to determine the initial concentrations of NH3 and NH4Cl in the buffer solution. Since they are both 0.1 M, the concentration of NH3 is also 0.1 M, and the concentration of NH4Cl is also 0.1 M.
When NaOH is added, it reacts with NH4Cl according to the following equation:
NaOH + NH4Cl → NH3 + H2O + NaCl
Since the concentration of NaOH is 0.1 M and the volume added is 6 ml (0.006 L), we can calculate the number of moles of NaOH added:
moles of NaOH = concentration x volume = 0.1 M x 0.006 L
Since NaOH reacts with NH4Cl in a 1:1 ratio, the same number of moles of NH4Cl will be converted to NH3. Therefore, the concentration of NH4Cl will decrease by the number of moles of NaOH added.
To calculate the new concentration of NH4Cl, we divide the moles of NH4Cl by the total volume of the buffer solution:
new concentration of NH4Cl = (initial concentration of NH4Cl x initial volume of NH4Cl) / total volume of buffer solution
Now that we have the new concentration of NH4Cl, we can calculate the new concentration of NH3 by subtracting it from the initial concentration of NH4Cl:
new concentration of NH3 = initial concentration of NH3 + initial concentration of NH4Cl - new concentration of NH4Cl
Finally, we can determine the change in pH using the Henderson-Hasselbalch equation, as explained earlier.
By following these steps, you can calculate the change in pH when HCl or NaOH is added to the given buffer solution.