Have you ever seen a colour change when two liquids are mixed in a chemistry lab? That’s often because of an acid base titration. It’s a simple and smart way to find out gow much acid or base is present in a solution. In this method, an acid is slowly added to a base until they completely react with each other. This process is widely used in labs, industries, and even medicine. In this article, we’ll break down what acid base titration is, how it works, and why it’s so important using simple examples, formulas, and easy explanations to help you prepare for exams.

What is Acid-Base Titration?

It’s a method used to obtain or find the unknown concentration of base or acid by neutralizing it with the known concentration of acid or base. In other words, it is an experimental technique used to find information about the solution that contains acid or base. Based on acidic or basic properties, many compounds can be determined by this method. The indicator is added to determine the endpoint. Moreover, the base is titrated with acid and acid is titrated with the base.

When a substance under study is dissolved in a solution, it forms an analyte. The solution is kept in a flask for titration, where a small amount of indicator and an analyte is added. The reagent is slowly added to the mixture through the burette. After some time, when the indicator causes a colour change, the amount of reagent used is recorded. Some titrations required a boiled solution due to the carbon dioxide formed by the reaction between acid and base. It reduces the accuracy of that when dissolved in water. So after boiling the solution, a large part of carbon dioxide is removed from the solution, which allows the titration to be more effective.

Titrations are recorded on the graph called titration curves. The volume of titrant, i.e., the independent variable is plotted through the x-axis. Whereas the pH of a solution which is the dependent variable is plotted through the y-axis. The point at which all the starting solutions are neutralized by the titrant is known as the equivalence point.

Acid-base titration includes strong/weak acids or bases. It is used to find out the concentration of acid or base. It is also used to know whether the unknown acid or base is strong or weak. It determines the pKa of an unknown acid or pKb of the unknown base. All reactions can not be considered titrations. So under some conditions, a reaction can be considered titration. The conditions are given below:

• The reaction should be fast.
• The reaction should proceed stoichiometrically.
• During the reaction, the change in free energy (△G) must be sufficiently large.
• To detect the completion of the result, there should be a way.

Classification Of Titration

Titrations are grouped based on the strength of the acid and base used. Here’s a quick breakdown:

1. Strong acid-strong base titration: In this titration, the acid and base will react to form a neutral solution. Hydronium (H+) and hydroxide(OH−) ions will react to form water at the equivalence point.

E.g., Hydrochloric acid and sodium hydroxide.

2. Weak acid – strong base titration: The weak acid strong base titration involves the direct transfer of protons from the weak acid to the hydroxide ion. The reaction of the acetic acid, a weak acid with sodium hydroxide, a strong base, is an example of this type of titration. Another example is as follows:

E.g., Ethanoic acid and sodium hydroxide.

3. Strong acid – weak base titration: In a strong acid weak base titration, the acid and base will react to form an acidic solution. In a titration, a conjugate acid is produced, which then reacts with water to form hydronium ions.

E.g., Hydrochloric acid and ammonia.

4. Weak acid – weak base titration: In a weak acid – weak base titration, however, the pH at the equivalence point is greater or less than 7.0 for weak acids and weak bases respectively. Before the equivalence point is reached, the pH tends to change more slowly in titrations of weak acids and weak bases than in titrations of strong acids and strong bases.

E.g., Ethanoic and ammonia.

Apparatus Used in Titration

To perform a titration, you need a few basic tools:

• Burette- to hold and slowly release the solution of known concentration
• Pipette- to measure and transfer a fixed volume of the unknown solution
• Conical Flask- to mix the solutions during the reaction
• White Tile- placed under the flask to easily see the colour change
• Indicator - helps you know when the reaction is complete 
• Clamp Stand & Funnel- for holding the burette steady and filling it safely

Procedure Of Acid-Base Titration

Following are the steps to note for acid-base titration.

Step 1: Choose your titrant and titrate and determine the normality of the titrate.

Step 2: Determine the amount of liquid you want to pipette out.

Step 3: Select an indicator and begin titration.

Step 4: Take note of the endpoint when the solution changes colour.

Step 5: Using the final reading, calculate the titrant’s normality.

The formula to calculate the titrant’s normality is molarity (M) of the acid x volume (V) of the acid = molarity (M) of the base x volume (V) of the base.

Indicators Used in Acid Base Titration

• Use phenolphthalein when titrating a strong base with a strong or weak acid. It turns colorless in acid and pink in base
• Use methyl orange when titrating a strong acid with a weak base. It turns red in acid and yellow in base

Titration Calculations with Examples

To calculate the strength of an unknown solution in titration, we use this basic formula:

N_1 V_1=N_2 V_2

Where: 

• N1= Normality of acid
• N2= Normality of base
• V1= Volume of acid
• V2= Volume of base

Example: Suppose we titrate 25 mL of NaOH with 0.1 N HCl and it takes 20 mL of HCl to reach the end point. Find the normality of NaOH?

Using the formula:

\begin{aligned}

& \mathrm{N}_1 \mathbf{V}_1=\mathrm{N}_2 \mathbf{V}_2 \\

& \rightarrow \mathrm{~N}_1 \times 25=0.1 \times 20 \\

& \rightarrow \mathrm{~N}_1=(0.1 \times 20) / 25 \\

& \rightarrow \mathrm{~N}_1=0.08 \mathrm{~N}

\end{aligned}

So, the normality of NaOH is 0.08 N.

Applications Of Acid-Base Titration

• The most common application of acid-base titrations is calculating an unknown analyte’s acid or base concentration.
• An analysis of the environment can be conducted with it.
• Pharmaceutical applications are possible by acid-base titration.
• Quantitative chemical analysis is carried out with acid-base titration.

Apart from this topic, you can study different reactions in Chemistry like displacement reaction, decomposition reaction, combination reaction, etc. You can also give mock tests and clear all your doubts. All of this is available on the Testbook App and you don't have to pay anything for that.