25. (10 points) Vinegar is a solution of acetic acid, HC2H,02. The label on a br

Question

25. (10 points) Vinegar is a solution of acetic acid, HC2H,02. The label on a brown rice vinegar claims the vinegar is 4.5% acidity, meaning the solution is 45% acetic acid by mass. (See Physical Properties and concentration lab for what this concentration unit means.) To test the validity of this claim, a sample of the vinegar was analyzed by titrating it with a sodium hydroxide solution. 11.50 mL of 1.0073 M NaOH was needed to completely react with the acetic acid in a 15.451 g sample of vinegar. is the claim on the label valid?

Explanation / Answer

Answer:

A pertinent equation for titration of AcOH against NaOH is,

AcOH + NaOH (aq) --------> AcONa + H2O

I.e. 1 mole NaOH = 1 mole of AcOH

Let us calculate # of moles of NaOH required.

Molarity of NaOH = 1.0073 M, Volume = 11.50 mL = 0.01150 L

# of Moles of NaOH = Molarity * Volume in L = 1.0073 * 0.01150 = 0.01158 moles.

From mole equivalence of this neutralization reaction we have,

# of Moles of AcOH = # of moles of NaOH = 0.01158 moles.

On multiplying # of moles of AcOH with it's Molar mass we get Mass of AcOH,

Molar Mass of AcOH = 60.05 g/mole.

Mass of AcOH = # of moles * Molar mass = 0.01158 * 60.05 = 0.696 g

Actual mass of AcOH in vinegar sample = 0.696 g.

But mass of Vinegar sample analyzed = 15.451 g

% AcOH = (Actual mass of AcOH / Mass of Vinegar) * 100

= (0.696/15.451) * 100

= 4.50 %

Yes the claim is true.

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