Question

In this lab, we will titrate NaOH into Binegar (acetic acid) to determine its concentration.

These are the principle questions:

- What is the reaction that occurs in this titration?

- What does a titration measure, and how does it measure this quantity?

- What is a titration curve? How would it differ for diprotic of triprotic acids?

- What is an equivalence point?

- How do you select an indicator?

Answer 1

CH₃COOH + NaOH    CH₃COONa + H₂O

Volumetric Titrations commonly comprise of

1. acid-base titrations

2. Oxidation-reduction or Redox titrations

3. Complexometric titrations

Acid-base titration: Solution of acids are titrated against standard alkali solution or vice versa. The process of acid-base titrations is accompanied by a change in pH.

Titration curve : A plot between pH of the solution during the titration and the amount of the acid or alkali added from a burette is called titration curve.

Equivalence point: It is the point at which the reaction between an acid and a base is theoretically complete(as per balanced equation of the reaction).

at equivalence point mEq of acid = mEq of base but the end point can only be detected by measuring the pH of different points of time during the titration.it is usually more convenient to add an indicator to the solution and detect the observed end of the reaction through a colour change in the solution.

Indicator: An indicator is a dye (or substance) which change colour over a short pH of range .an indicator is usually a weak acid or a weak base for acid-base titration.The colour change occurs when protons are transferred to form a conjugate base or a conjugate acid of a different colour.Select an indicator that change colour at a pH that is as close as possible to equivalence point.means pH at equivalent point will fall with in the range over which indicator changes colour see the table of indicators in picture.Indicators are frequently employed in detectin end points in acid-base titrations.