3) 0.3382 g of an unknown diprotic acid, when dissolved in water, required 32.34 mL of 0.1046 M KOH to reach the endpoint. Calculate the molar mass of the unknown acid.
Also, for this problem I keept getting 99 close to 100 g/mol, but the answer has to be 200 g/mol, so can someone plz explain how you get 200g/mol?
H2A + 2KOH ==> H2A + 2H2O
mol KOH = 0.1046*0.03234 = 0.0033876
mol H2A = 1/2 that or 0.0016914
mol = g/molar mass or
molar mass = g/mol = 0.3382/0.0016914 =199.95 which I would round to 200.0 to 4 s.f.
Thank you for your help and time!
To calculate the molar mass of the unknown diprotic acid, we can use the concept of stoichiometry and the balanced chemical equation of the acid-base reaction.
1) Begin by writing the balanced chemical equation for the reaction between the unknown diprotic acid (HA) and potassium hydroxide (KOH). Since KOH is a strong base and diprotic acids have two acidic protons, the equation will look like this:
2HA + 2KOH → 2K^+ + 2H2O + H2A
In this equation, 2 moles of the acid react with 2 moles of KOH to produce 2 moles of water and 1 mole of the diprotic acid H2A.
2) Next, we need to determine the number of moles of KOH used in the reaction. We can calculate this using the equation:
moles of KOH = volume of KOH solution (in L) × molarity of KOH (in mol/L)
Given that the volume of KOH solution is 32.34 mL and the molarity of KOH is 0.1046 M, we convert the volume to liters and substitute the values into the equation:
moles of KOH = 0.03234 L × 0.1046 mol/L = 0.00338 mol
3) Now, we need to find the number of moles of the diprotic acid (H2A) based on the stoichiometry of the balanced equation. Since 2 moles of KOH react with 1 mole of H2A, the moles of H2A can be calculated as:
moles of H2A = (moles of KOH) / 2 = 0.00338 mol / 2 = 0.00169 mol
4) Finally, to determine the molar mass of the unknown diprotic acid (H2A), we can use the equation:
molar mass (in g/mol) = mass of the acid (in g) / moles of the acid
Since we are given that the mass of the acid is 0.3382 g and we have determined the moles of H2A as 0.00169 mol, we substitute the values into the equation:
molar mass = 0.3382 g / 0.00169 mol = 200 g/mol
Therefore, the molar mass of the unknown diprotic acid is 200 g/mol, not 99 g/mol.