It would be a bit surprising if a chemistry student says that he or she has never witnessed titration being performed in their school laboratory. If you remember a chemist dropwise adding a liquid through a long glass tube into a conical glass flask which leads to a color change in the flask, then the good news is, you are already familiar with titration.
We know that titration is a chemical analysis process, but what is its background chemistry, origin, method, applications, and need? In short, everything you need to know about titrations and/or titrimetry is covered in this article. So, let’s dive into it.
What is titration – Definition
Titration is a chemical analysis process. It is used to determine the unknown quantity or amount of a chemical substance by reacting it with a measured quantity of another chemical substance. The chemical constituent whose quantity is unknown is known as the titrand, while the substance of known concentration is called the titrant or titrator. The process of chemically reacting the titrand with the titrant is known as titration.
There are many different types of titrations, such as acid-base titration, redox titration, complexometric titration, etc. The combined study of all these different types of titrations, their methods, chemistry and applications is collectively called titrimetry.
What is the difference between titrant and titrand
As we already mentioned, titrant and titrand are the two principal components of a titration experiment. Let’s see how they are different from each other, as mentioned in the table below.
|The chemical constituent of exactly known concentration. It is also known as a standard solution.||The chemical constituent whose concentration is unknown. It is also known as the analyte solution.|
|It is used to determine the quantity of the unknown chemical substance||It is the one whose concentration is to be determined using the titrant|
|Usually added dropwise via a long-graduated glass tube known as a burette||Usually taken in a conical flask called a titration flask|
The glass apparatus required for titration
- Volumetric flask: It is used to prepare the standard solution.
- Titration flask: It is used for holding the titrand or analyte and mixing it with the titrant while the titration reaction is being performed. The titration flask is also known as an Erlenmeyer flask.
- Pipette: It is used for precisely measuring and transferring the titrant into the titration flask.
- Burette: It is used for holding and for the dropwise addition of the standard solution or titrant into the titration mixture.
All the glassware must be first thoroughly washed and rinsed with distilled water, followed by appropriate drying for it to be employed in the titration experiment.
Now let us understand how a titration experiment is actually performed through the steps given in the next section.
How is a titration experiment performed
Step I: Preparation of the standard solution
The first step while performing a titration experiment is to prepare the standard solution, which is then used as the titrant.
A known amount of a chemical substance called the solute is weighed and dissolved in a specific volume of a solvent to obtain a solution of the desired concentration.
The chemical substance to be used for the preparation of the standard solution must be a primary standard, i.e., ultrapure. If it is not a primary standard, it can be standardized to determine its exact concentration before titration. In that case, it is known as a secondary standard. Absolute sulfuric acid (H2SO4) and oxalic acid (H2C2O4) are primary standards, while hydrochloric acid (HCl) is an example of a secondary standard.
Different units of concentration can be used for the preparation of the standard solution, such as molarity, molality, normality, parts per million (ppm), etc.
To prepare a 0.1 M (molar) solution of sulfuric acid (H2SO4), you need to weigh 2.45 grams of H2SO4 in a 250 mL volumetric flask.
This concentrated sulfuric acid is then diluted with distilled water up to the 250 mL mark on the volumetric flask. This gives us a 0.1 M standard solution of H2SO4 prepared in distilled water, achieving a total solution volume of 250 mL.
You can further dilute this solution by applying the stock dilution formula, i.e., C1V1 = C2V2 where C1= initial concentration, C2= final desired concentration, V1 = volume of the solution with C1 concentration and V2 = final volume that needs to be prepared.
Also note that a 1 Molar H2SO4 solution = 2 Normal H2SO4 solution so 0.1 M = 0.2 N H2SO4. In this way, the concentration units are interconvertible. But we are not concerned with all of it in this introductory article, so let’s move to the next titration step.
Step II: The burette is filled with the standard solution of known concentration (titrant)
The burette is filled with the solution of known concentration, i.e., the titrant.
The burette is a long, graduated glass tube with a stop-clock and a delivery tube at its bottom end. Burettes come in different sizes, such as a 10 mL burette, a 25 mL burette, a 50 mL burette and even a 500 mL burette is available. But it depends upon the experimental need for which the burette is to be used. However, a burette with a maximum capacity of holding 50 mL titrant is the standard protocol for a titration experiment.
If it is a colorless solution, the solution volume is read by keeping your eye level parallel to the lower meniscus (curved surface of the liquid), avoiding parallax error. Contrarily for recording the volume of a colored solution, such as a purple solution of potassium permanganate (KMnO4), as commonly used in redox titrations, the upper meniscus is read.
Thus, in this example, the burette is filled with 0.1 M H2SO4 solution prepared in step I. This is known as the titrant because its concentration is known.
Step III: A precise volume of the analytical solution (titrand) is pipetted out in the titration flask
In this step, a precise volume such as 10 mL of titrand i.e., NaOH in the above example is precisely measured using a pipette and added into the titration flask.
Step IV: A few drops of the indicator are added to the titration flask.
The most commonly used indicators for an acid-base titration are methyl orange and phenolphthalein. The indicator is a chemical substance that does not participate in the chemical reaction, but it gives a visible color change as the titrant reacts with the titrand.
For example, phenolphthalein gives a light pink color as a few drops of it are added into the titration flask containing 10 mL of NaOH solution. A specific amount of titrand (such as NaOH) reacts with H2SO4 and a neutralization reaction occurs. But the moment the concentration of hydrogen (H+) ions exceeds the hydroxide (OH–) ions in the titration flask, phenolphthalein immediately changes color from light pink to colorless.
This color change marks the completion of the reaction and is known as the endpoint. The indicator is chosen such as its endpoint coincides with the equivalence point for the chemical reaction taking place in the titration mixture. The equivalence point for an acid-base reaction is when H+ ions = OH– ions in the reaction mixture.
Step V: The titrant is added dropwise into the titration mixture
The titrant is added from the burette into the titration flask containing the reaction mixture (titrand + indicator) in a dropwise manner. The chemist needs to have firm control over the burette stop-clock while adding the titrant into the titration flask. Also, the titration flask should be continuously stirred throughout the experiment to ensure a uniform mixing of the two chemical constituents.
The stop-clock should be instantly closed the moment the indicator changes color, and the volume of titrant used must be immediately noted down from the burette.
This is the titre volume used against 10 mL of titrand or analyte solution present in the titration flask.
Steps 2-5 are repeated thrice at least, and the titre volume and other data are tabulated to obtain the unknown titrand concentration. The three volume readings should ideally fall within a difference ± 0.1 units to ensure that the results obtained are precise and accurate, thus reliable.
Step VI: The unknown concentration is determined using titration data
We have provided you with a supposed calculation as per the example we followed in the above sequence. However, you need to insert the actual data when performing this experiment in your chemistry laboratory and make the calculations accordingly.
|Initial burette reading (mL)||Final burette reading (mL)||Titre volume (mL)|
|0||10.0||10-0 = 10.0|
|10.0||20.1||20.1-10.0 = 10.1|
|20.1||30.0||30.0 – 20.1 = 9.9|
|Mean volume of titrant used against 10 mL of titrand
= (10 + 10.1 + 9.9) /3 = 10 mL
The balanced chemical equation for an acid-base neutralization reaction between H2SO4 and NaOH is:
H2SO4 (aq) + 2 NaOH (aq) = Na2SO4 (aq) + 2 H2O(l)
Applying stoichiometric principles, the equation above shows that 1 mole of sulfuric acid (H2SO4) reacts with 2 moles of sodium hydroxide (NaOH) base in a complete neutralization reaction to produce salt (Na2SO4) and water (H2O). In the titration reaction, we used 10 mL of 0.1 M H2SO4 to neutralize 10 mL of x M NaOH. The value of x can be determined from the titration formula given below.
M1 = 0.1 M, V1 = 10 mL, n1 = 1
M2 = x, V2 = 10 mL, n2 = 2
Result: This titration experiment helped us determine the unknown concentration of the titrand (NaOH in this case), i.e., 0.2 M.
As a titration experiment is based on the quantitative analysis of a chemical substance by taking precise volume measurements hence titration is popularly known as a volumetric analysis technique.
Different types of titration
The many different types of titrations are mainly classified based on the chemical reaction occurring between the titrant and the sample solution or titrand.
- Acid-base titration: The titration used for determining the unknown concentration of an acid or base via a neutralization reaction with the standard solution.
- Redox titration: The titration based on an oxidation-reduction reaction. Iodometry and iodimetry are sub-types of redox titration.
- Complexometric titration: The titration based on a ligand-metal complexation reaction.
- Potentiometric titration: The potentiometric titration is a type of titration in which the end point is marked via a change in potential difference.
All these different types of titrations will be discussed in our subsequent articles in the titration series. So, stay connected.
You may also like: What are those 8 different types of titrations in chemistry.
What is titration used for
Titration is the simplest and an extremely valuable chemical analysis method which is used for:
- Determining the unknown concentration of analytes in the chemical laboratory,
- In the analysis of food and beverage ingredients,
- In the manufacturing of cosmetic products,
- Wastewater analysis, etc.
Titration is primarily used as a first step for quantitative analysis of newly synthesized and/or extracted and purified products in research and development before sending them for more extensive instrumental protocols such as chromatography and spectroscopy.
You may find other uses and applications of titration here.
1. C. Harris, D. (2010). Quantitative Chemical Analysis, 8th Edition, W.H Freeman and Company.
2. Townshend, A. (2005). TITRIMETRY | Overview. Encyclopedia of Analytical Science (Second Edition). P. Worsfold, A. Townshend and C. Poole. Oxford, Elsevier: 105-113.