In standardizing a potassium hydroxide solution, a student finds that 32.60mL of the base solution is needed to titrate 0.5045 grams of KHP to a phenolphthalein end point. In another titration, 26.63mL of this same base solution is needed to titrate 0.2003grams of an unknown solid monoproctic acid.
1. Determine the molarity of the base solution
2.Determine the molar mass of the unknown solid monoproctic acid.
To determine the molarity of the base solution, we need to use the amount of KHP (potassium hydrogen phthalate) that was titrated and the volume of the base solution that was needed.
1. Determine the molarity of the base solution:
First, let's calculate the number of moles of KHP in the first titration:
moles of KHP = mass of KHP / molar mass of KHP
The molar mass of KHP can be found using the periodic table:
molar mass of KHP = molar mass of potassium (K) + molar mass of hydrogen (H) + molar mass of phthalate (C8H5O4)
Next, we calculate the molarity of the base solution:
molarity of base = moles of KHP / volume of base solution
2. Determine the molar mass of the unknown solid monoprotic acid:
Using the same principle, we can calculate the molar mass of the unknown monoprotic acid using the mass of the acid and the number of moles of base solution required for titration.
First, let's calculate the number of moles of the unknown monoprotic acid in the second titration:
moles of acid = volume of base solution x molarity of base solution
Then, we can calculate the molar mass of the acid:
molar mass of acid = mass of the acid / moles of acid
Now, let's substitute the given values into the equations and calculate the answers:
Given:
- Volume of base solution in first titration = 32.60 mL = 0.03260 L
- Mass of KHP in first titration = 0.5045 g
- Volume of base solution in second titration = 26.63 mL = 0.02663 L
- Mass of unknown acid in second titration = 0.2003 g
1. Determine the molarity of the base solution:
molar mass of KHP = molar mass of K + molar mass of H + molar mass of phthalate
= (39.10 g/mol) + (1.01 g/mol) + (291.14 g/mol)
= 331.25 g/mol
moles of KHP = mass of KHP / molar mass of KHP
= 0.5045 g / 331.25 g/mol
= 0.0015258 mol
molarity of base = moles of KHP / volume of base solution
= 0.0015258 mol / 0.03260 L
= 0.04678 M
Therefore, the molarity of the base solution is 0.04678 M.
2. Determine the molar mass of the unknown solid monoprotic acid:
moles of base solution in second titration = volume of base solution x molarity of base solution
= 0.02663 L x 0.04678 M
= 0.001243 mol
molar mass of acid = mass of acid / moles of acid
= 0.2003 g / 0.001243 mol
= 161.13 g/mol
Therefore, the molar mass of the unknown solid monoprotic acid is 161.13 g/mol.