A 0.12 g sample of unknown was placed in a flask and dissolved in 125 mL of deionized water. A solution of HCl (0.10 M) was used to titrate the sample, and 18 mL was required to reach the endpoint. What is the formula weight of the unknown?
The problem doesn't establish that this is a mono, di, or triprotic base but I assume one(1) OH group and we shall call it B + HCl ==> BH^+ + Cl^-
How many moles HCl did we add to reach end point? That is M x L = ??
moles base = same as mole HCl added.
moles = grams/molar mass
You know moles and grams, solve for molar mass.
To find the formula weight of the unknown substance, we need to use the concept of stoichiometry and the balanced chemical equation. Here are the steps to calculate the formula weight:
Step 1: Determine the number of moles of HCl used in the titration.
Since the molarity (M) of HCl is given as 0.10 M, and the volume of HCl used is 18 mL (which we can convert to liters by dividing by 1000):
moles HCl = Molarity (M) × Volume (L)
moles HCl = 0.10 mol/L × 0.018 L
moles HCl = 0.0018 mol
Step 2: Use the balanced chemical equation to determine the mole ratio between HCl and the unknown substance.
The balanced chemical equation for the reaction between HCl and the unknown substance is required to determine this mole ratio.
Step 3: Use the mole ratio to calculate the number of moles of the unknown substance.
Once we know the mole ratio between HCl and the unknown substance, we can calculate the number of moles of the unknown substance.
moles unknown substance = moles HCl × mole ratio
Step 4: Finally, calculate the formula weight of the unknown substance.
Formula weight (FW) is calculated by dividing the mass of the sample by the number of moles.
FW = Mass (g) / Moles
FW = 0.12 g / moles unknown substance
By following these steps and using the given information, we can find the formula weight of the unknown substance.