A student is performing a titration of an acetic acid sample . She pipets a 10.0

Question

A student is performing a titration of an acetic acid sample . She pipets a 10.00mL sample of vinegar into her Erlenmeyer flask, adds 25 mL of Dl water and a few drops of phenolphthalein indicator to the flask. She then namalizes and fills the buret with 0.2437 M NaOH solution. She drains some standard out of the tip of the buret and removes air bubbles. She reads her buret before she begins titrating. The reading is 5.24mL. She then adds the NaOH standard from the buret into the Erlenmeyer flask until one drop causes the solution to turn color and remain pink for 1 Minute. She reads the buret and her final reading is 26.85mL.

1. Write the balanced chemical equation

2. What is the volume of NaOH used in the titration?

3. How many moles of NaOH are in this volume of solution?

4. How many moles of acetic acid were neutralized by the NaOH?

5. What is the molarity of the acetic acid in the vinegar sample?

Explanation / Answer

a ) Na+(aq) + OH-(aq) + CH3COOH(aq) ------> CH3COO-(aq) + Na+(aq) + H2O(l)
but it's better if u write the equation as follows:
NaOH(aq) + CH3COOH(aq) ----------> CH3COONa(aq) + H2O(l)
It is the balanced equation & the salt formed is CH3COONa known as Sodium Acetate

2 ) Volume of NaOH used = final reading of the burrete - initial reading = 26.85- 5.24 = 21.61 ml of NaOH

3 ) 0.2437 M NaOH solution = moles of NaOH / volume in litre = moles of NaOH / 0.021

=> moles of NaOH = 0.2437 * 0.021 = 0.0051 moles

4 ) The Vinegar is probably 5% acetic acid by volume, so first find the volume of Acetic acid in solution.

.05*10=0.5ml
then you have to use the density of acetic acid to convert from volume to mass density= 1.05 g/mL
0.5 mL * 1.05 g/mL = 0.525 grams
then convert from grams to moles using the molar mass=60.05
0.525 grams/60.05 g/mole = 0.0087 moles Acetic acid in 10 mL Vinegar with 5% acetic acid (HC2H3O2).

5 )

we know N1V1 = N2V2

so 0.2437 * 21.61 = N2 * 0.5

=> N2 = 10.532 M = strength of acetic acid

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