It is found that 42.5 mL of 1.02 mol/L NaOH have been added to 50.0 mL of vinegar (ethanoic acid) when the phenolphthalein in the solution just turns pink. What is the concentration of the vinegar?

0.867mol/L

Explanation:

Step 1:

The balanced equation for the reaction. This is given below:

CH3COOH + NaOH —> CH3COONa + H2O

From the balanced equation above,

The mole ratio of the acid (nA) = 1

The mole ratio of the base (nB) = 1

Step 2:

Data obtained from the question.

Volume of base, NaOH (Vb) = 42.5mL

Molarity of base, NaOH (Mb) = 1.02mol/L

Volume of acid, CH3COOH (Va) = 50mL

Molarity of acid, CH3COOH (Ma) =..?

Step 3:

Determination of the molarity of the acid solution.

This can be obtained as follow:

MaVa /MbVb = nA/nB

Ma x 50 / 1.02 x 42.5 = 1

Cross multiply

Ma x 50 = 1.02 x 42.5

Divide both side by 50

Ma = (1.02 x 42.5) /50

Ma = 0.867mol/L

Therefore, the concentration of the vinegar is 0.867mol/L.