Question

	Trial one	Trial two	Trial three
Volume of oxalic acid (mL)	10.1 mL	10.2 mL	10.1 mL
Moles of oxalic acid (moles)	0.0026	0.0026	0.0026
Initial volume of NaOH (mL)	18.7 mL	26.5 mL	34.6 mL
Final volume of NaOH (mL)	26.5 mL	34.6 mL	42.6 mL
Delivered volume of NaOH (moles)	7.8 mL	8.1 mL	8 mL
Moles of NaOH (moles)	0.0052	0.0052	0.0052
Molarity of NaOH (M)	0.6667	0.6420	0.65
Average Molarity NaOH (M)	0.65

Concentration oxalic acid (M) = 0.2567

Data for the Determination of Acetic Acid in Vinegar portion of the Titration of Vinegar Experiment:

	Trial one	Trial two	Trial three
Volume of acetic acid sol’n (mL)	10	10	10
Moles of acetic acid sol’n (moles)	0.00835	0.0083	0.0083
Initial volume of NaOH (mL)	2.8	15.65	28.45
Final volume of NaOH (mL)	15.65	28.45	41.2
Delivered volume of NaOH (mL)	12.85	12.8	12.75
Average Molarity of NaOH (M) *See table 1*	0.65
Molarity of acetic acid (M)	0.8350	0.83	0.83
Average molarity of acetic acid (M)	0.83

Titration of Vinegar Lab

CH3CO2H + Na+(OH)-  --> CH3CO2- Na+ + HOH

H2C2O4 + 2 Na+ (OH)- ---> 2Na+ (C2O4)2- + 2H2O

wt/wt% = 4.96%

2 drops of Phenophthalein is used in the titration.

- What is an equivalence point and how is it recognized in this experiment?

Answer 1

Equivalence point refers to a point in titration when a volume of titrant has been added such that equivalent of OH- and H+ become equal are are exactly neutralised by each other.

for example here when equivalent of OH- (supplied by NaOH) and H+ (CH3COOH) become equal and neutralisation occurs we observe equivalence point

For detecting equivalence point during titration we use the indicator phenolphthalien which shows colour change at equivalence point.

This colour change is because phenolphthalien is a weak acid and when no more acetic acid is left in the solution OH- attack phenolphthalien which is colourlesswhich leads to change of phenolphthalien to its conjugate base ion which has pink colour. Hence this colour change detect the volume of titratnt at which equivalence point is obtained.