Using the standardized NaOH solution, the student weighs out 0.2550g of a solid unknown acid and finds that 28.50mL of the NaOH solution is required to reach an end point with the acid. Calculate the molar mass of the unknown acid, assuming the acid is diprotic.
H2A + 2NaOH ==> Na2A + 2H2O
mols NaOH = M x L = ?
mols H2A = 2 x mols NaOH from the coefficients in the balanced equation.
mols H2A = grams H2A/molar mass H2A
To calculate the molar mass of the unknown acid, we need to use the concept of the balanced chemical equation and the stoichiometry of the reaction.
In this case, the reaction between the unknown acid (HA) and the NaOH solution can be represented as follows:
2HA + 2NaOH -> Na2A + 2H2O
From the balanced equation, we can see that two moles of the unknown acid (HA) react with two moles of NaOH to form one mole of Na2A and two moles of water.
Given that 28.50 mL of the NaOH solution is required to react with the unknown acid, we can convert it to moles using the molarity of the NaOH solution.
To do this, we need to know the concentration of the NaOH solution in units of moles per liter (M). Let's say the concentration is C M.
First, calculate the number of moles of NaOH used in the reaction:
moles NaOH = volume (in liters) × concentration (in M)
moles NaOH = 28.50 mL × (1 L / 1000 mL) × C M
Since the reaction is 1:1 between NaOH and HA, the number of moles of the unknown acid (HA) is also equal to moles NaOH.
Next, calculate the molar mass of the unknown acid (HA) using the given mass and the moles of the unknown acid:
Molar mass (g/mol) = mass (g) / moles
Molar mass (g/mol) = 0.2550 g / moles
Finally, substitute the value of moles (obtained from the moles of NaOH) into the equation to find the molar mass of the unknown acid.