a buffer is made by adding 150 ml of .595M BaF2 and 0f .500M of HF solution.
calculate the pH of this buffer system
calculate the pH of this buffer after adding .100 mol Hcl
calculate the pH of this buffer after adding .0750 mol Ca(OH)2
ka(HF)= 6.9x10^-4
kb(F-)= 1.4 x 10^-11
Use the Henderson-Hasselbalch equation; BUT I don't think you can make a 0.6 M solution of BaF2. It isn't that soluble is it. Ksp is about 10^-6.
im confused on how to calculate the pH of this buffer after adding .100 mol Hcl ... i get negative numbers
You write the two equations for what goes on in the buffer solution.
F^- + H^+ ==> HF
So when you add acid (HCl), you decrease the F^- moles and you increase the HF moles. So for final base it is what you had initially - moles H^+ added. For final acid, it is what you had initially + moles H^+ added. Plug those new values into the log(base/acid) terms and recalculate. It won't change the pH very much.
i got ph= 3.24+log -7
b/c i did
ph=3.24 = log .175/-.025
It almost 24 hours since we worked on this. If you still need it, repost at the top of the page and I'll try to go through it with you.
no thank you
To calculate the pH of the buffer system, we first need to find the concentrations of the relevant species in solution.
For the initial buffer solution:
1. Calculate the moles of BaF2:
moles = volume (in L) x concentration (in mol/L)
moles of BaF2 = 0.150 L x 0.595 mol/L = 0.08925 mol
2. Calculate the moles of HF:
moles of HF = 0.500 L x 0.500 mol/L = 0.250 mol
3. Calculate the total volume of the solution:
total volume = volume of BaF2 + volume of HF
total volume = 0.150 L + 0.500 L = 0.650 L
4. Calculate the concentration of BaF2 in the buffer solution:
concentration of BaF2 = moles of BaF2 / total volume
concentration of BaF2 = 0.08925 mol / 0.650 L = 0.137307 mol/L
5. Calculate the concentration of HF in the buffer solution:
concentration of HF = moles of HF / total volume
concentration of HF = 0.250 mol / 0.650 L = 0.384615 mol/L
Now, we can calculate the pH of the buffer solution using the Henderson-Hasselbalch equation:
pH = pKa + log([A-] / [HA])
where [A-] is the concentration of the conjugate base (F-) and [HA] is the concentration of the acid (HF).
Given that ka(HF) = 6.9x10^-4, we can find the pKa:
pKa = -log(ka(HF))
pKa = -log(6.9x10^-4) = 3.16
Using this pKa value, we can now calculate the pH of the buffer system:
pH = 3.16 + log(0.137307 / 0.384615)
pH = 3.16 + log(0.35639)
pH = 3.16 - 0.44997
pH = 2.71003
So, the pH of the buffer system is approximately 2.71.
To calculate the pH of the buffer after adding 0.100 mol of HCl, we need to consider the reaction of HCl with the HF in the buffer. Since HCl is a strong acid, it will fully dissociate into H+ and Cl- ions.
1. Calculate the new concentration of HF after adding HCl:
moles of HF = initial moles of HF - moles of HCl
moles of HF = 0.250 mol - 0.100 mol = 0.150 mol
2. Calculate the new volume of the buffer solution after adding HCl:
total volume = initial total volume + volume of HCl
total volume = 0.650 L + 0.0 L (neglecting volume of HCl)
3. Calculate the new concentration of HF in the buffer solution after adding HCl:
concentration of HF = moles of HF / total volume
concentration of HF = 0.150 mol / 0.650 L = 0.230769 mol/L
Now, we can recalculate the pH using the Henderson-Hasselbalch equation:
pH = pKa + log([A-] / [HA])
pH = 3.16 + log(0.137307 / 0.230769)
pH = 3.16 + log(0.59585)
pH = 3.16 - 0.22576
pH = 2.93424
So, the pH of the buffer after adding 0.100 mol of HCl is approximately 2.93.
To calculate the pH of the buffer after adding 0.0750 mol of Ca(OH)2, we need to consider the reaction of Ca(OH)2 with the F- ion in the buffer. Since Ca(OH)2 is a strong base, it will fully dissociate into Ca2+ and OH- ions.
1. Calculate the new concentration of F- after adding Ca(OH)2:
moles of F- = initial moles of F- - moles of Ca(OH)2
moles of F- = 0.08925 mol - 0.075 mol = 0.01425 mol
2. Calculate the new volume of the buffer solution after adding Ca(OH)2:
total volume = initial total volume + volume of Ca(OH)2
total volume = 0.650 L + 0.0 L (neglecting volume of Ca(OH)2)
3. Calculate the new concentration of F- in the buffer solution after adding Ca(OH)2:
concentration of F- = moles of F- / total volume
concentration of F- = 0.01425 mol / 0.650 L = 0.021923 mol/L
Now, we can recalculate the pH using the Henderson-Hasselbalch equation:
pH = pKa + log([A-] / [HA])
pH = 3.16 + log(0.021923 / 0.230769)
pH = 3.16 + log(0.095087)
pH = 3.16 - 0.02201
pH = 3.13799
So, the pH of the buffer after adding 0.0750 mol of Ca(OH)2 is approximately 3.14.