A solution of the primary standard potassium hydrogen phthalate, KHC8H4O4, was prepared by dissolving 0.4877 g of potassium hydrogen phthalate in about 50 mL of water. Titration with a KOH solution required 24.71 mL to reach a phenolphthalein end point. What is the molarity of the KOH solution?
The titration is a 1:1 titration of KHP and KOH.
KOH + KHP ==> H2O + K2P
mols KHP = grams/molar mass
mols KOH = mols KHP (look at the coefficients in the balanced equation; they are 1:1)
M KOH = mols KOH/L KOH
To determine the molarity of the KOH solution, we can use the equation:
Molarity of KOH = (Molarity of the standard solution * Volume of the standard solution) / Volume of KOH solution used
First, let's calculate the molarity of the potassium hydrogen phthalate (KHP) solution.
Step 1: Calculate the number of moles of KHP used.
Moles of KHP = Mass of KHP / Molar mass of KHP
The molar mass of KHP (potassium hydrogen phthalate) is:
1 * atomic mass of K + 1 * atomic mass of H + 4 * atomic mass of C + 4 * atomic mass of H + 4 * atomic mass of O
= (1 * 39.10) + (1 * 1.01) + (4 * 12.01) + (4 * 1.01) + (4 * 16.00)
= 204.22 g/mol
Moles of KHP = 0.4877 g / 204.22 g/mol = 0.0023865 mol
Step 2: Calculate the molarity of the KHP solution.
Molarity of KHP = Moles of KHP / Volume of KHP solution (in liters)
Given that the volume of the KHP solution is 50 mL, we need to convert it to liters:
Volume of KHP solution = 50 mL / 1000 mL/L = 0.05 L
Molarity of KHP = 0.0023865 mol / 0.05 L = 0.04773 M
Step 3: Use the molarity of KHP to calculate the molarity of KOH.
Molarity of KOH = (Molarity of KHP * Volume of KHP solution) / Volume of KOH solution used
Given that the volume of KOH solution used is 24.71 mL, we need to convert it to liters:
Volume of KOH solution used = 24.71 mL / 1000 mL/L = 0.02471 L
Molarity of KOH = (0.04773 M * 0.05 L) / 0.02471 L = 0.0961 M
Therefore, the molarity of the KOH solution is 0.0961 M.
To find the molarity of the KOH solution, we need to set up a balanced chemical equation for the reaction between potassium hydrogen phthalate (KHC8H4O4) and KOH.
The balanced equation for this reaction is:
KHC8H4O4 + KOH -> K2C8H4O4 + H2O
From the balanced equation, we can see that the mole ratio between KHC8H4O4 and KOH is 1:1. This means that the number of moles of KOH used in the titration is equal to the number of moles of KHC8H4O4 present in the solution.
First, let's calculate the number of moles of KHC8H4O4:
Given mass of KHC8H4O4 = 0.4877 g
Molar mass of KHC8H4O4 = 204.23 g/mol
Number of moles of KHC8H4O4 = Mass / Molar mass
= 0.4877 g / 204.23 g/mol
Next, we need to calculate the molarity of KOH solution. Molarity (M) is defined as moles of solute per liter of solution.
Number of moles of KOH = Number of moles of KHC8H4O4
Molarity of KOH solution = Moles of KOH / Volume of KOH solution
The volume of KOH solution used in the titration is given as 24.71 mL. To convert this to liters:
Volume of KOH solution (L) = 24.71 mL / 1000 mL/L
Now we can substitute the values into the equation to find the molarity of the KOH solution.