An analytical chemist weighs out 0.225g of an unknown diprotic acid into a 250mL volumetric flask and dilutes to the mark with distilled water. He then titrates this solution with 0.0700M NaOHsolution. When the titration reaches the equivalence point, the chemist finds he has added 38.7mL of NaOH solution. Calculate the molar mass of the unknown acid.
To calculate the molar mass of the unknown diprotic acid, we first need to determine the number of moles of NaOH used in the titration.
Step 1: Calculate the number of moles of NaOH used.
First, convert the volume of NaOH solution used (38.7 mL) to liters:
38.7 mL = 38.7 mL * (1 L / 1000 mL) = 0.0387 L
Then, use the volume and concentration of NaOH to calculate the number of moles:
moles of NaOH = volume (L) * concentration (M)
moles of NaOH = 0.0387 L * 0.0700 M = 0.002709 moles NaOH
Step 2: Calculate the number of moles of the unknown diprotic acid.
Since NaOH is a strong base and diprotic acid is a weak acid, the reaction between them occurs in a 1:2 ratio:
NaOH + H2A → NaA + H2O
This means that for every 1 mole of NaOH used, 2 moles of diprotic acid (H2A) react.
Therefore, moles of H2A = 2 * moles of NaOH = 2 * 0.002709 moles = 0.005418 moles
Step 3: Calculate the molar mass of the unknown diprotic acid.
Molar mass (g/mol) = mass (g) / moles
Molar mass = 0.225 g / 0.005418 moles = 41.53 g/mol
Therefore, the molar mass of the unknown diprotic acid is approximately 41.53 g/mol.
To calculate the molar mass of the unknown diprotic acid, we need to use the information provided and understand the stoichiometry of the reaction between the acid and the NaOH solution.
1. First, let's determine the number of moles of NaOH that were added to reach the equivalence point.
Moles of NaOH = concentration of NaOH × volume of NaOH solution
= 0.0700 M × 0.0387 L
= 0.002709 moles
2. Next, we need to consider the balanced equation for the reaction between the diprotic acid and NaOH. Since the acid is diprotic, it will require 2 moles of NaOH to neutralize 1 mole of acid.
3. From the balanced equation, we can determine the moles of unknown acid present in the solution.
Moles of acid = 0.002709 moles × (1 mole acid / 2 moles NaOH)
= 0.0013545 moles
4. Now, we can calculate the molar mass of the unknown acid.
Molar mass = mass of acid / moles of acid
= 0.225 g / 0.0013545 moles
= 166.017 g/mol
Therefore, the molar mass of the unknown acid is approximately 166.017 g/mol.
H2A + 2NaOH ==> Na2A + 2H2O
mols NaOH = M x L = ?
mols H2A must be 1/2 that (look at the coefficients).
mols H2A = grams/molar mass. You know mols and grams, solve for molar mass.