You dissolve 1.05 grams of an unknown diprotic acid in 200.0 mL of H2O. This solution is just neutralized by 5.00 mL of a 1.00 M NaOH solution. What is the molar mass of the unknown acid?
H2A + 2NaOH ==> 2H2O + Na2A
mols NaOH = M x L = ?
mols H2A = 1/2 that (from the coefficients in the equation).
mols H2A = grams H2A/molar mass H2A. You have grams and mols, solve for molar mass.
To find the molar mass of the unknown diprotic acid, we need to follow these steps:
Step 1: Calculate the number of moles of NaOH used for neutralization.
Step 2: Determine the number of moles of H+ ions in the diprotic acid solution.
Step 3: Use the moles of H+ ions to find the number of moles of the unknown acid.
Step 4: Calculate the molar mass of the unknown acid.
Let's go through each step in detail:
Step 1: Calculate the number of moles of NaOH used:
Since the NaOH solution is 1.00 M, we can use the following formula:
Moles of solute (NaOH) = Concentration (M) × Volume (L)
Moles of NaOH = 1.00 mol/L × 5.00 mL × (1 L / 1000 mL)
Moles of NaOH = 0.005 mol
Step 2: Determine the number of moles of H+ ions:
Since NaOH is a strong base and the solution is neutralized, the number of moles of H+ ions must be equal to the number of moles of OH- ions. The reaction between NaOH and the diprotic acid is as follows:
2 NaOH + H2A → Na2A + 2 H2O
Since NaOH has a 1:2 stoichiometric ratio with the diprotic acid, 0.005 mol of NaOH will react with 0.0025 mol of the diprotic acid.
Step 3: Use the moles of H+ ions to find the number of moles of the unknown acid:
The molar mass of a substance is calculated by dividing the mass by the number of moles. Since we know the mass of the unknown acid (1.05 grams), we need to determine the number of moles. In this case, we found 0.0025 mol of the diprotic acid.
Step 4: Calculate the molar mass of the unknown acid:
Molar mass of the unknown acid = Mass (g) / Moles
Molar mass = 1.05 g / 0.0025 mol
Molar mass = 420 g/mol
Therefore, the molar mass of the unknown diprotic acid is 420 g/mol.
To find the molar mass of the unknown diprotic acid, we need to use the stoichiometry of the neutralization reaction and the given information.
Let's break down the steps to solve this problem:
Step 1: Write the balanced equation for the neutralization reaction.
Since NaOH (sodium hydroxide) is a strong base and the acid is diprotic (can donate two protons), the balanced equation is as follows:
2NaOH + H2A -> Na2A + 2H2O
Step 2: Determine the moles of NaOH used.
We know that the volume of NaOH solution used is 5.00 mL, and the concentration of NaOH solution is 1.00 M. Using the formula C = n/V, where C is the concentration, n is the moles, and V is the volume, we can calculate the moles of NaOH used as follows:
n(NaOH) = C(NaOH) × V(NaOH)
n(NaOH) = 1.00 M × 5.00 mL
n(NaOH) = 0.00500 moles (because we converted mL to L)
Step 3: Determine the number of moles of the diprotic acid.
According to the balanced equation, the mole ratio between NaOH and the acid is 2:1. Therefore, the moles of diprotic acid used in the neutralization reaction is twice the moles of NaOH used:
n(H2A) = 2 × n(NaOH)
n(H2A) = 2 × 0.00500 moles
n(H2A) = 0.0100 moles
Step 4: Determine the molar mass of the diprotic acid.
The molar mass is the mass of the sample divided by the number of moles. In this case, the mass of the acid is given as 1.05 grams, so we divide it by the moles calculated in step 3 to find the molar mass:
Molar Mass(H2A) = Mass(H2A) / n(H2A)
Molar Mass(H2A) = 1.05 g / 0.0100 moles
Molar Mass(H2A) = 105 g/mol
Therefore, the molar mass of the unknown diprotic acid is 105 g/mol.