Question

A titration of 25.00 mL of O.1550 M HCl solution with a solution of NaOH of unknown molarity starts at a buret reading for NaOH of 0.33 mL The phenolphthalein indicator turns light pink the acid solution for over 30 seconds at a buret reading of 24.19 mL

2) What was the volume of HCl you started with?

3) How many moles of HCl were in the original solution?

4) Write the balanced chemical equation for the titration reaction.

5) How many moles of NaOH were delivered with the buret?

6) What was the volume of NaOH dispensed?

7) What is the Molarity of the unknown NAOH solution?

Answer 1

Solution:-

Given data

Volume of HCl =25.00 mL (0.0250 L)

Molarity of HCl =0.1550 M

Initial burette reading =0.33 mL

Final burette reading =24.19 mL

#2) Volume of the HCl solution started with = 25.00 mL

#3) Moles of HCl in the original solution.

Moles =molarity * volume in liter

Moles of HCl =0.1550 mol per L * 0.0250 L

                        = 0.003875 mol

#4) Balanced reaction equation is as follows

HCl +NaOH ---- > NaCl + H2O

#5)Using the mole ratio of the balanced equation we can find the moles of NaOH as follows

The mole ratio of the HCl and NaOH is 1:1

(0.003875 mol HCl)*(1 mol NaOH)/(1 mol HCl) =0.003875 mol NaOH

#6) Volume of NaOH = final burette reading – initial burette reading

                                         =24.19 mL – 0.33 mL

                                          =23.86 mL

#7) Calculating molarity of unknown NaOH

Volume of NaOH =23.86 mL =0.02386 L

Molarity = moles/ volume

                =(0.003875 mol)/(0.02386 L)

                =0.1624 M

Molarity of unknown NaOH is 0.1624 M