How To Carry Out a Titration Experiment

A titration experiment is the gradual adding of a known concentration of a reagent, called a titrant, to an unknown concentration of an analyte (the substance being analysed) until an endpoint is reached. Titration is one of the classic experiments in chemistry, and it’s done by most students at school. 

Usually, chemical indicators that change colour are used to determine the endpoint of a titration experiment. However, depending on the type of substances to be titrated, an indicator may not be necessary. In some cases, the analyte acts as an indicator.

What is a Titration Experiment?

A titration experiment can be done using various methods, depending on the chemicals being analysed, the purpose, and the scale. Many different industries have specific titration methods for specific chemicals and processes. Nonetheless, the fundamental principles involved stay the same.

A titration experiment is a simple and inexpensive means of determining the concentration of a solution that’s being analysed. It doesn’t require a complicated apparatus, only a graduated burette with a stopcock, a metal support stand, a burette clamp, a funnel, a flask or beaker, and an indicator. This basic setup applies for both school chemistry experiments and large industrial laboratories.

To carry out the experiment, you simply need a sample of a known solution, an unknown concentration and subject it to the titration process. For example, if you have a large batch of vegetable oil that your factory needs to process into biofuel, you may need to adjust the concentration of the lye (alkali) to properly convert it. In this case, you wouldn’t need to have cubic metres of samples to test its concentration. Instead, you’d only need to get a few litres or even milliliters of samples to be titrated.

Soap manufacturing is another sector that uses titration experiments to gain precise calculations of the ingredients needed for mass-producing various types of soaps. Determining the saponification number is essential when calculating how much lye is necessary. This number is the amount of base needed to hydrolyse a specific amount of fat to produce free fatty acids in a soap mixture.

Experimentally determining the saponification number is necessary because not all fat and oil raw materials have the same exact saponification number. Therefore, the amount of base in the solution must be adjusted accordingly.

5 Erlenmeyer flasks lined up on laboratory desk, each with different coloured solutions inside
In some titration experiments, chemical indicators that change colour are used to indicate the endpoint of titration

What is the Aim of a Titration Experiment?

All titration experiments, regardless of the type, chemicals involved, complexity, or scale, have one main purpose: to determine the concentration of the analyte. This is achieved through the gradual addition of the titrant (which has a known concentration) and carefully measuring its volume until an endpoint is reached.

Going back to the saponification example, you can use the result of a titration experiment to determine the concentration of base needed to hydrolyse the fatty acids. It’s just a matter of proportion, and knowing both the volume and concentration of one solution (the titrant). Knowing the volume of another solution of unknown concentration will allow you to plug the numbers and make some calculations.

Remember that molarity of a solution can be calculated by dividing the moles or molar value of the solute by the litres of solution. Therefore, by rearranging our formula, the moles of a solute are equal to the molarity of a solution multiplied by the volume in litres:

moles of solute = M x V

This formula is very useful once you plug in the results of a titration experiment. You can easily calculate the molarity or concentration of the analyte. In an acid-base titration experiment, for instance, we can write the molarity formula for the balanced or endpoint reaction between acids and bases as:

M(a) x V(a) = M(b) x V(b)

The subscript (a) represents acid while the subscript (b) represents base.

How To Do a Redox Titration

Redox titration is just one of the four main types of titration experiments. The other types are acid-base, precipitation, and complexometric titrations. As the name implies, redox titration involves the reaction between a reducing and an oxidising agent.

Many of us are very familiar with acid-base titrations that involve the reactions between acids and bases. The key point to remember in this type of reaction is that hydrogen ions are transferred between the reactants. In comparison, redox titrations involve the change of the oxidation number of at least one element as electrons are transferred.

Some of the most common redox titrations are:

  • Permanganate titrations
  • Dichromate titrations
  • Iodimetric and iodometric titrations

The exact steps of redox titrations vary depending on the substances involved. However, there are some general stages you can follow:

  1. You must write down the half balanced equation for the reduction side and another half balanced equation for the oxidation side
  2. You then add the two equations together to have a redox reaction equation
  3. Perform the experiment to collect data. Many redox titration experiments require indicators, but some do not
  4. Once you have collected the data, you can now calculate the mole ratios of the reactants
Diagram showing the different stages of a titration experiment

How To Do a Back Titration

Back titration is a reverse titration. It involves the addition of excess titrant to a standard molar concentration to an analyte. In this experiment, the excess is titrated instead of the original sample. 

This method works well when the endpoint of the reverse titration can be easily identified, like in precipitation titrations. Back titrations are also good if the reactions between the titrant and the analytes are slow, or when the analyte is insoluble in water.

How To Do a Back Titration Calculation

Adding an excess titrant to an analyte then titrating the new solution will indirectly determine the original concentration of the analyte. It will take a two-part calculation to determine the original concentration of the analyte. This example from Socratic shows you the basic steps and calculations for a back titration:

Problem: 50.00 mL of 0.1000 mol/L HCl is added to 25.00 mL of a commercial ammonia-based cleaner. It required 21.50 mL of 0.1000 mol/L NaOH to neutralise the excess hydrochloric acid. 

What is the original concentration of ammonia in the cleaner?

Solution: We must assume that some HCl was neutralised when added in the ammonia solution. However, since the acid concentration is excessive, the new solution is acidic and needs to be neutralised using sodium hydroxide.

Part 1 – Calculations for the acid

  1. Calculate the moles of HCl added to the solution. Based on the given concentrations in mL, we can then convert it to L and get the corresponding concentration of 0.005 mol
  2. Calculate the moles of sodium hydroxide used. Again, through simple conversions, we get 0.00215 mol NaOH
  3. Calculate the mole of excess HCl. Similarly, we get 0.00215 mol HCL
  4. Calculate how much moles of HCL reacted with ammonia. You simply need to subtract the moles of the acid from the moles of ammonia: 0.00500 mol – 0.00215 mol = 0.002850 mol

Part 2 – Calculations for the ammonia

  1. Calculate the moles of ammonia. You need to convert it to the right unit, which is 0.002 850 mol NH3
  2. Calculate the molarity of ammonia
Equation for calculating the moles of ammonia in a back titration experiment

How To Do a Titration Write Up

Just like other types of scientific reports that are required from you by your teacher or employer, you need to be brief, to the point, precise, and data-driven when writing about a titration experiment. The statement of the problem must be clear. 

You must have an introduction that explains the experiment and why you chose that method. Be clear about your methodology and instruments. Explain how you prepared the solutions. More importantly, focus on data presentation, describing the reactions, and the measurements that you’ve made.

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