Question

Find concentration of a weak acid given Volume of unknown acid, Molarity of bass(NaOH), and mL of bass(NaOH) at equalivance point.

Volume unkown acid: 10mL

Molality of bass: .18M

mL bass at equvilance point: 6.1mL

Find molarity of acid: ?

Answer 1

At equivalence point the number of moles of acid = no. of moles of base

So, millimoles of base if we add 6.1 ml of 0.18 M base = molarity*volume in ml

= 0.18M*6.1ml = 1.098 millimoles

lets say that the molarity of acid = x M

so, millimoles of acid in 10 ml of x M acid = molarity*volume in ml

= xM*10ml = 10x millimoles

Equating the millimoles at equivalence point -

10x millimoles = 1.098 millimoles

so, x = 1.098/10 M = 0.1098 M

So, molarity of acid = x = 0.1098 M