Question

Using the above sodium hydroxide solution, 27.21 mL of the NaOH solution is required to neutralize a volume of 28.45 mL of an acetic acid solution having an unknown concentration to a phenolphthalein end point. Determine the concentration, in molarity, of the acidic solution. Start with a balanced equation.

Answer 1

A balanced equation-

CH₃COOH (aq) + NaOH (aq) ------> H₂O (l) + NaCH₃COO (aq)  

Suppose 28.45 mL sodium hydroxide solution is 0.10 M

Calculate the number of moles of NaOH -

Number of moles of NaOH = molarity of NaOH x volume of NaOH in L

                                                = 0.10 moles/L x 27.21/1000

                                                = 0.002721 moles

The balanced equation shows 1:1 stoichiometry

So, moles of acid reacting = moles of base reacting

Moles of CH₃COOH = 0.002721 moles

Volume of CH₃COOH reacted = 28.45 mL = 0.02845 L

Molarity of CH₃COOH

M _acid = moles _acid / V _acid

            = 0.002721 moles /0.02845 L

            = 0.0956M

Concentration, in molarity = 0.0956M