Acid Base Titration

An acid-base titration is a technique that is in use to experiment and acquire information about a solution containing an acid or base.  As you are aware, there are hundreds of compounds, organic as well as inorganic. With the help of Titration, one can determine their acidic or basic properties. Acid is titrated with a base, and a base (alkali) is titrated with an acid. The use of an indicator decides the endpoint in Titration. Acid-base titrations are in use to calculate the amount of a known acidic or basic substance through acid-base reactions. The word Titration comes from the Latin word titulus, which means an inscription or a title. In the French language, the word title means a rank. Hence, Titration implies the determinations of concentration or rank of a solution with respect to water with a pH of 7. A standard solution is added from an apparatus known as the burette. The process of adding a standard solution until the reaction is complete is called Titration. The substance to be determined is understood to be titrated.

What is Acid - Base Titration? 

It is essential to note that all reactions in chemistry are not titrations.  A reaction can get a reference as Titration only if it satisfies specific conditions. Here are a few conditions that help to determine whether a reaction is a titration

  1. The reaction has to be fast

  2. The change in free energy during the reaction must be large enough for the spontaneity of the reaction.

  3. There must always be a way to decide the completion of the reaction.

(image will be uploaded soon)

The Endpoint and The Equivalent Point in a Titration

The endpoint of a reaction is the stage that shows the completion of the reaction. The endpoint is detected by a physical change that is produced by the solution itself or by the addition of a reagent known as an indicator. The equivalent point is a stage where the amount of reagent added is exactly equivalent to the amount of the reacting substance in the titrated solution. Ref.Fig.1.

It is important to note that the endpoint and the equivalence point may not be identical. The endpoint is typically detected only after the addition of a slight excess amount of the titrant. If there is a difference between the endpoint and the equivalent point, then it amounts to an error in the experiment. 

Acid - Base Titration Example

It is essential to measure accurately the volumes when doing titrations. The instrument in use for titration is called the burette. It is a type of liquid dispensing system that can indicate the volume of a liquid with precision. 

Let us take an example 

Suppose, 25.66 ml or 0.02566 L of 0.1078 M HCL was used to titrate an unknown sample of NaOH. What mass of NaOH was in the sample? 

We can calculate this by the number of moles of HCL reacted by: 

mol HCL = (0.02566) (0.1078 M) = 0.002766 mol HCL 

We also have a balanced chemical equation reaction between HCL and NaOH: 

HCL + NaOH = NaCL + H2

So, now we can construct a conversion factor to convert a number of moles of NaOH that reacted.

0.002766 mol HCL x 1 mol NaOH /1 mol HCL   = 0.002766 mol NaOH 

Now, we can convert this amount to mass using the molar mass of NaOH (40.00G/mol) 

0.002766 mol HCL x  40.00 g NaOH / 1 mol HCL = 0.1106 g NaOH.

The mass of NaOH in the sample is 0.1106 g. This calculation is part of Titration. 

Key Terms used in Acid - Base Titration 

  1. Titration - is the process where a solution of unknown strength adds to a specific volume of treated sample that contains an indicator.

  2. A titrant - is a solution of known strength of concentration in use in titration.

  3. A Titrant is any solution to which the titrant adds and which contains the ion that is being determined.

  4. The Titration curve is a plotting of pH versus millilitres of titrant showing how pH changes versus millilitres of titrant during an acid-base titration.  

  5. The Equivalent point- is the point at which the reagent is added to react completely with a substance.

  6. A Buffer solution- is that solution that resists changes in pH levels even when a strong acid or base is added or when it dilutes with water.

FAQ (Frequently Asked Questions)

Q1. What are the Learning Objectives for Titration?

The learning objectives include finding reasons for the reaction of an acid with a base to make a salt and water, common in any lab because so many compounds act as acids and base. Another reason is that acid-base reactions are very common – hence they are widely in use to determine the quantitative amount of one or the other. Now, the performing of chemical reaction to quantitatively determine the precise amount of a reagent is known as the titration process. A Titration can be done with almost any chemical reactions for which we know the balanced chemical equation.

Q2. How do the Indicators Work in Titration?

When we perform an acid-base titration reaction, an acid with a known concentration or a standard solution is gradually added to a base that has an unknown strength. The process can be vice-versa too. Now, a few drops of an indicator solution are added to a base. The indicator will give a signal with a change in the colour of the solution. When the base is neutralised (when H+ = OH-) At this point, which is called the equivalent point or endpoint, the titration stops. When we know about the volumes of the acid and the base used, and the concentration of the standard solution, calculations let us determine the concentration of the other solution.