A 80.0 mL volume of 0.25 M HBr is titrated with 0.50M KOH. Calculate the pH after addition of 40.0 mL of KOH.
HBr + KOH ==> KBr + HOH
moles HBr initially = L x M = ?
moles KOH added = L x M = ?
See which is in excess and calculate pH from pH = -log (H^+). OR
if mole HBr = moles KOH, the the solution has just KBr and H2O and calculate pH from that. Post your work if you need additional assistance.
Find the moles of HBr = (liters)(M)
Find the moles of KOH = (liters(M)
If moles of HBr = moles KOH, pH = 7
If moles of HBr is larger than moles KOH, the mixture is acid and
[H+] = [(moles HBr)-(moles KOH)]/(total liters)
pH = -log[H+]
If moles of KOH is larger than moles of HBr,
[OH-] = [(moles KOH)-(moles HBr)]/(total liters)
pOH = -log[OH-]
and
pH = 14-pOH
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To calculate the pH after the addition of 40.0 mL of KOH, we need to determine the number of moles of HBr and KOH, and then use the stoichiometry of the reaction to find the concentration of the resulting solution. Finally, we can use the concentration of the resulting solution to calculate the pH.
Step 1: Calculate the moles of HBr present in the initial solution.
The volume of the HBr solution is given as 80.0 mL, and the concentration is 0.25 M. To calculate the moles of HBr, we can use the formula:
moles = concentration × volume (in liters)
First, convert the volume of HBr solution to liters:
80.0 mL ÷ 1000 = 0.0800 L
Then calculate the moles of HBr:
moles of HBr = 0.25 M × 0.0800 L
Step 2: Calculate the moles of KOH added.
The volume of KOH solution added is given as 40.0 mL, and the concentration is 0.50 M. Using the same formula as above, convert the volume to liters and calculate the moles of KOH.
Step 3: Determine the limiting reactant.
Since HBr and KOH react in a 1:1 ratio according to the balanced chemical equation:
HBr + KOH → KBr + H2O
The reactant with fewer moles will be completely consumed and limit the formation of the products. Compare the moles of HBr and KOH to determine the limiting reactant.
Step 4: Calculate the concentration of the resulting solution.
Since the balanced chemical equation shows a 1:1 ratio between HBr and KOH, the moles of KOH added will be equal to the moles of HBr consumed (assuming KOH is the limiting reactant).
To determine the volume of the resulting solution, add the volumes of HBr and KOH:
80.0 mL + 40.0 mL = 120.0 mL = 0.120 L
The total moles of HBr in the resulting solution will be equal to the initially present moles of HBr minus the moles of HBr consumed (equivalent to the moles of KOH added).
Step 5: Calculate the concentration of the resulting solution.
To calculate the concentration, divide the moles of HBr in the resulting solution by the volume of the resulting solution:
concentration = moles / volume (in liters)
Step 6: Calculate the pH.
To calculate the pH, we need to determine the concentration of H+ ions in the resulting solution. Since HBr is a strong acid, it will dissociate completely in water.
Since the concentration of the resulting solution is now known, the concentration of H+ ions will be the same as the concentration of HBr in the resulting solution.
Finally, calculate the pH using the formula:
pH = -log[H+]
By following these steps, you will be able to calculate the pH after the addition of 40.0 mL of KOH to an 80.0 mL volume of 0.25 M HBr.