Acid and Base Titration

Molarity quantitive analysis, knowledge of acid and bases.

Acid-Base Titrations Chemistry Quick insight of an Acid-Base Titration Calculation

Titration

Titration, which is also known as titrimetry is a common laboratory method of quantitive chemical analysis that is used to determine the unknown molarity of an acid or base. Titration is adding measured volumes of an acid or base of known molarity to a base or acid of unknown molarity until neutralization occurs. Since, volume measurements play a key role in titration, it is also known as volumetric analysis.

The most common types of titration is acid-base titrations.

Acid-Base Titration

An acid-base titration is a neutralization reaction that is performed in the lab in order to determine an unknown concentration of acid or base. The moles of acid will equal the moles of base at the equivalence point. Here's how to perform the calculation to find your unknown.

For example, if you are titrating hydrochloric acid with sodium hydroxide:

HCl + NaOH → NaCl + H2O


You can see from the equation there is a 1:1 molar ratio between HCl and NaOH. If you know that titrating 50.00 ml of an HCl solution requires 25.00 ml of 1.00 M NaOH, you can calculate the concentration of hydrochloric acid, [HCl]. Based on the molar ratio between HCl and NaOH you know that at the equivalence point:

moles HCl = moles NaOH

MHCl x volumeHCl = MNaOH x volumeNaOH

MHCl = MNaOH x volumeNaOH / volumeHCl

MHCl = 25.00 ml x 1.00 M / 50.00 ml

MHCl = 0.50 M HCl


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Get Ready for Action!!!

Before starting the titration a suitable pH indicator must be chosen. The equivalence point of the reaction, the point at which equivalent amounts of the reactants have reacted, will have a pH dependent on the relative strengths of the acid and base used. The pH of the equivalence point can be estimated using the following rules:

  1. A strong acid will react with a strong base to form a neutral (pH = 7) solution.
  2. A strong acid will react with a weak base to form an acidic (pH < 7) solution.
  3. A weak acid will react with a strong base to form a basic (pH > 7) solution

Recording Data

Titration are often recorded on graphs called titration curves, which usually contain the volume of the titrant as the independent variable and the pH of the solution as the dependent variable because it changes depending on the composition of the two solutions.

The equivalence point on the graph is where all the starting solution has been neutralized by the base. This endpoint of titration is the point when the indicator changes color.

At this point moles H+ = OH-.


The pH of a weak solution being titrated with a strong base solution can be found at different points along the way. These points fall into one of four categories:

  1. initial pH
  2. pH before the equivalence point
  3. pH at the equivalence point
  4. pH after the equivalence point


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BASIC TITRATIONS

Basic Titrations - Chemistry Tutorial