PART A)
Suppose that 6.9 mL of 2.5 M KOH(aq)
is transferred to a 250 mL volumetric flask
and diluted to the mark. It was found that
32.8 mL of this diluted solution was
needed to reach the stoichiometric point in a
titration of 6.9 mL of a phosphoric acid solution
according to the reaction
3 KOH(aq) + H3PO4(aq) →
K3PO4(aq) + 3 H2O(ℓ)
Calculate the molarity of the solution.
Answer in units of M.
PART B)
What mass of H3PO4 is in the sample of the
acid solution?
Answer in units of g.
I have estimated all of these calculation so it will be necessary for you recalculate all of them.
I assume you mean to calculate the molarity of the H3PO4 solution but that isn't clear in the problem. mols KOH initially = M x L = about 0.02
You diluted this to 250 mL and drew a 32.8 mL aliquot so mols in the 32.8 mL is
about 0.02 x 32.8/250 = about 0.002,
Convert mols KOH to mols H3PO4 using the coefficients in the blanced equation you gave. That's about 0.002 mols KOH x (1 mols H3PO4/3 mol KOH) = about 0.002/3 - approx 0.0007 mols H3PO4.
So concn H3PO4 = mols H3PO4/L H3PO4 = about 0.0007/0.006.9 = ?
If instead of M H3PO4 you wanted M KOH in the diluted solution it is M = mols KOH/LKOH = abouat 0.02/0.250 = ?
Part B. You have M H3PO4. You want to know grams H3PO4 in the 6.9 mL
mols H3PO4 = M x L = ?
mols H3PO4 = grams/molar mass. You know mol and molar mass, substitute and solve for grams.
Post your work if you get stuck.
PART A:
To calculate the molarity of the solution, we need to use the given information about the volumes and concentrations of the solutions involved.
First, let's calculate the moles of KOH used in the dilution:
moles of KOH = volume of KOH solution (in L) * concentration of KOH (in M)
moles of KOH = 6.9 mL * (1 L / 1000 mL) * 2.5 M
moles of KOH = 0.01725 mol
Next, let's determine the moles of KOH reacted during the titration:
According to the balanced equation, the stoichiometric ratio between KOH and H3PO4 is 3:1. Therefore, if 0.01725 mol of KOH reacted, then 1/3 of that amount reacted with H3PO4:
moles of H3PO4 = moles of KOH * (1/3)
moles of H3PO4 = 0.01725 mol * (1/3)
moles of H3PO4 = 0.00575 mol
Now, let's determine the molarity of the H3PO4 solution:
molarity of H3PO4 = moles of H3PO4 / volume of H3PO4 solution (in L)
molarity of H3PO4 = 0.00575 mol / (32.8 mL * (1 L / 1000 mL))
molarity of H3PO4 = 0.1753 M
Therefore, the molarity of the solution is 0.1753 M.
PART B:
To calculate the mass of H3PO4 in the sample, we need to use the molarity of the H3PO4 solution and the volume of the H3PO4 solution used in the titration.
First, let's calculate the moles of H3PO4 in the solution:
moles of H3PO4 = molarity of H3PO4 * volume of H3PO4 solution (in L)
moles of H3PO4 = 0.1753 M * (32.8 mL * (1 L / 1000 mL))
moles of H3PO4 = 0.0057464 mol
Now, let's determine the molar mass of H3PO4:
molar mass of H3PO4 = 1(1.01 g/mol) + 3(16.00 g/mol) + 1(31.00 g/mol)
molar mass of H3PO4 = 98.01 g/mol
Finally, let's calculate the mass of H3PO4 in the sample:
mass of H3PO4 = moles of H3PO4 * molar mass of H3PO4
mass of H3PO4 = 0.0057464 mol * 98.01 g/mol
mass of H3PO4 = 0.563 g
Therefore, the mass of H3PO4 in the sample is 0.563 g.
To solve this problem, we need to use the stoichiometry of the reaction and the volume information provided to calculate the molarity of the solution and the mass of H3PO4 in the sample.
PART A) Calculating the molarity of the solution:
Step 1: Determine the number of moles of KOH transferred to the volumetric flask.
To do this, we use the formula:
Number of moles = Molarity × Volume (in liters)
Given that the volume transferred is 6.9 mL and the molarity of KOH is 2.5 M:
Number of moles of KOH = (2.5 M) × (6.9 mL / 1000 mL/L) = 0.01725 moles
Step 2: Calculate the number of moles of KOH in the diluted solution used in the titration.
Since the volume used in the titration is 32.8 mL, we can find the number of moles using the same formula as in Step 1:
Number of moles of KOH in the diluted solution = (2.5 M) × (32.8 mL / 1000 mL/L) = 0.082 moles
Step 3: Apply the stoichiometry of the reaction to determine the ratio between KOH a