I took 6.22 g of potassium hypochlorite and dissolved it up in a 100.0 mL flask.
I then added 8.00 mL of 2.00 M nitric acid. The solution should be able to buffer that addition.
How much more (mLs) of the nitric acid can the system take before it is no longer in the buffer zone?
I took 6.22 g of potassium hypochlorite and dissolved it up in a 100.0 mL flask.
I then added 8.00 mL of 2.00 M nitric acid.
The solution should be able to buffer that addition.
How much more (mLs) of the nitric acid can the system take before it is no longer in the buffer zone?
mols KOCl = 6.22g/90.55 = 0.0687 or 68.7 millimols.
......OCl^- + H^+ ==> HOCl
I....68.7.....0........0
add..........16.............
C...-16.....-16........16
E....52.7.....0.........16
You can substitute to find the pH of this solution is 8.05
Out of the buffer range for pKa of 7.53 is 6.53.
Take the E line from above and add in x amount.
E ...52.7......0.......16
add............x.........
new C -x......-x.......+x
new E 52.7-x...0.......16+x
6.53 = 7.53 + log (52.7-x)/(16+x)
x = ? millimols HNO3. I think x is about 46 but you should confirm. Convert to mL of 2 M with M = millimols/mL
You should check it out. You added 16 mmols first, add to the 46 (or whatever number it is) to the 16. That gives OCl^- of 52.7-46 and HOCl of 16 + 46. Again, make sure these numbers are right and I noted that you must use 3 places to get the 6.53 pH.
Post your work if you get stuck.
To determine how much more nitric acid the system can take before it is no longer in the buffer zone, we need to calculate the buffer capacity of the solution. The buffer capacity is a measure of the amount of acid or base that can be added to a buffer solution without causing a significant change in its pH.
To calculate the buffer capacity, we need to know the concentrations of the components of the buffer, which in this case are potassium hypochlorite (KClO) and its conjugate base, hypochlorous acid (HOCl). The balanced equation for the ionization of KClO in water is:
KClO(aq) + H2O(l) ⇌ K+(aq) + ClO-(aq) + HOCl(aq)
Given that you dissolved 6.22 g of KClO in a 100.0 mL flask, we can calculate the concentration of KClO using its molar mass.
Molar mass of KClO:
39.10 g/mol (K) + 35.45 g/mol (Cl) + 16.00 g/mol (O) = 90.55 g/mol
Concentration of KClO:
(6.22 g / 90.55 g/mol) / 0.1 L = 0.6866 M
Now, we need to calculate the buffer capacity. The buffer capacity can be approximated using the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Where pH is the desired pH of the buffer, pKa is the acid dissociation constant of the weak acid, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid.
Assuming that the pH of the buffer is close to the pKa of the weak acid, we can rearrange the equation as follows:
pH - pKa ≈ log([A-]/[HA])
Since you mentioned that the solution can buffer the addition of 8.00 mL of 2.00 M nitric acid, we can assume that the initial pH is close to the pKa of HOCl. The pKa of HOCl is approximately 7.53.
So, we have:
pH - 7.53 ≈ log([ClO-] / [HOCl])
Given that the concentration of KClO is 0.6866 M, we assume that the initial concentration of HOCl is also 0.6866 M.
0.6866 M / [HOCl] = 10^(pH - 7.53)
Now, we can calculate the buffer capacity using the equation:
Buffer Capacity = ([HOCl] + [A-]) x Volume of the solution
Since we are working with a 100.0 mL flask, the volume of the solution is 0.100 L.
Buffer Capacity = (0.6866 M + 0.6866 M) x 0.100 L = 0.13732 mol
To determine how much more nitric acid the system can take before it is no longer in the buffer zone, we need to calculate the amount of nitric acid that will react with the remaining HOCl and convert it to Cl-.
Since the balanced equation for the reaction between nitric acid (HNO3) and HOCl is as follows:
HOCl(aq) + HNO3(aq) → Cl-(aq) + H2O(l) + NO2(g)
And the stoichiometry of the reaction shows that 1 mole of nitric acid reacts with 1 mole of HOCl, we can calculate the amount of nitric acid that will react with the remaining HOCl as follows:
Amount of nitric acid = (0.6866 M) x (8.00 mL / 1000 mL/L) x (0.100 L) = 0.00549 mol
To find out how much more nitric acid can be added before the system is no longer in the buffer zone, we subtract the amount of nitric acid that will react with the remaining HOCl from the buffer capacity:
Remaining buffer capacity = 0.13732 mol - 0.00549 mol = 0.13183 mol
Finally, we can calculate the volume of the nitric acid that can still be added by dividing the remaining buffer capacity by the concentration of the nitric acid:
Volume of nitric acid = Remaining buffer capacity / Concentration of nitric acid
Given that the concentration of the nitric acid is 2.00 M:
Volume of nitric acid = 0.13183 mol / (2.00 mol/L) = 0.0659 L = 65.9 mL
Therefore, the system can still take approximately 65.9 mL more of the nitric acid before it is no longer in the buffer zone.