What is the concentration of the HNO3 solution?

Question

A 0.100L  sample of an unknown  solution required 28.5ml of 0.150 for complete neutralization. What is the concentration of the HNO3 solution?

Answer 1

Since it is a neutralization reaction, I'll assume the unknown is a base which that reacts in a 1:1 mole ratio with the acid, HCl, such as R-OH, and not R(OH)₂ or R(OH)₃, etc. This is basically a poorly written question (no pun intended)

moles HCl used = 28.5 ml x 1 L / 1000 ml x 0.150 mol/L = 0.004275 moles HCl

moles unknown = 0.004275 moles since assumed a 1:1 mole ratio

Concentration of unknown = moles/liter = 0.004275 moles / 0.1 L

Concentration of unknown = 0.04275 M = 0.0428 M (3 sig. figs.)