Question

A titration of 20.00 mL of an unknown HCl solution with 0.2350 M NaOH starts at a buret reading for NaOH of 0.350 mL. The phenolphthalein indicator turns light pink in the acid solution for over 30 seconds at a buret reading of 25.14 mL. Maintain 3 significant figures but do not include the units.

a. What was the volume of NaOH dispensed?

b. How many moles of NaOH were dispensed?

c. How many moles of HCl are present in the acid solution?

d. What is the molarity of the unknown HCl solution?

Answer 1

(a.) volume of NaOH dispensed (mL) = 24.8

(b.) moles of NaOH were dispensed (mol) = 0.00583

(c.) moles of HCl are present in the acid solution (mol) = 0.00583

(d.) molarity of the unknown HCl solution (M) = 0.291

Explanation

volume of NaOH dispensed = final buret reading - initial buret reading

volume of NaOH dispensed = 25.14 mL - 0.350 mL

volume of NaOH dispensed = 24.79 mL

volume of NaOH dispensed = 0.02479 L

moles NaOH dispensed = (molarity NaOH) * (volume NaOH)

moles NaOH dispensed = (0.2350 M) * (0.02479 L)

moles NaOH dispensed = 0.00583 mol

moles HCl present = mole NaOH dispensed

moles HCl present = 0.00583 mol

molarity HCl = (moles HCl present) / (volume HCl)

molarity HCl = (0.00593 mol) / (20.00 x 10^-3 L)

molarity HCl = 0.291 M