Volumetric Calculations: Introduction, Terms, Titration

Volumetric Calculations: Do you know how soap is manufactured? The manufacture of soap requires a particular number known as the saponification number. It is the amount of base needed to hydrolyze a certain amount of fat to produce the fatty acids that are required in the manufacture of soaps. The fatty acid is heated with a known amount of base (usually \({\rm{NaOH}}\) or \({\rm{KOH}}\)). After hydrolysis is complete, the leftover base is titrated to determine how much of it was needed to hydrolyze the fat sample. All these processes require volumetric calculations. Let’s understand how these calculations are done.

Volumetric Analysis

The technique of Volumetric Analysis is a typical way of determining the concentration of an unknown substance. This method entails mixing a known volume of a standard solution with a known volume of an unknown concentration solution. It is also known as titration

Steps Involved in Volumetric Analysis

• A pipette is used to measure a known volume (aliquot) of solution into a conical flask.
• Dispense the unknown other solution slowly into the conical flask through a burette.
• Observing the endpoint when indicator just changes colour and measure volume (titre) dispensed.
• The above steps are repeated until three concordant titre results (no more than \({\rm{0.1}}\,{\rm{mL}}\) difference between all three) is obtained, then average the concordant results to minimize errors.

Volumetric Analysis Terms

• When the colour of the solution changes, this is the endpoint.
• Titre refers to the amount of solution dispensed from the burette.
• Aliquot- a known volume of solution delivered from a pipette; 
• Concordant titres- those within a specified range, such as \({\rm{ + / – 0.1}}\,{\rm{ml}}\).
• An instrument for transferring a known volume of solution from a volumetric flask to a conical flask is known as a pipette.
• Burette — a device used to hold the unknown solution

Titration Calculations

At the equivalence point in a neutralization, the moles of acid is equal to the moles of base.

moles acid \(=\) moles base

The moles of the solute divided by the litres of the solution is the molarity \(\left( {\rm{M}} \right)\) of a solution \(\left( {\rm{L}} \right)\). As a result, the molarity of a solution multiplied by the volume in litres equals the moles of solute.

moles of solute \({\rm{ = M \times L}}\)

We can then set the moles of acid equal to the moles of base.

\({{\rm{M}}_{\rm{A}}}{\rm{ \times }}{{\rm{V}}_{\rm{A}}}{\rm{ = }}{{\rm{M}}_{\rm{B}}}{\rm{ \times }}{{\rm{V}}_{\rm{B}}}\)

\({{\rm{M}}_{\rm{A}}}\) is the acid’s molarity, while the molarity of the base is \({{\rm{M}}_{\rm{B}}}\). The volumes of the acid and base are \({{\rm{V}}_{\rm{A}}}\) and \({{\rm{V}}_{\rm{B}}}\), respectively.

Suppose we need \({\rm{20.70}}\,{\rm{mL}}\) of \({\rm{0.500}}\,{\rm{M}}\,{\rm{NaOH}}\) to achieve the endpoint when titrating against \({\rm{15.00}}\,{\rm{mL}}\) of unknown concentration \({\rm{HCl}}\). The molarity of the acid can be calculated using the equation above.

\({{\rm{M}}_{\rm{A}}}{\rm{ = }}\frac{{{{\rm{M}}_{\rm{B}}}{\rm{ \times }}{{\rm{V}}_{\rm{B}}}}}{{{{\rm{V}}_{\rm{A}}}}}{\rm{ = }}\frac{{{\rm{0.500}}\,{\rm{M \times 20}}{\rm{.70\;mL}}}}{{{\rm{15}}{\rm{.00\;mL}}}}{\rm{ = 0.69}}\,{\rm{M}}\)

In this scenario, the acid’s higher molarity compared to the base indicates that a lesser volume of acid is required to achieve the equivalence point.

Indicators

• During acid-base titration, an indicator is designed to estimate the reaction’s endpoint. The colour of an acid-based indicator is determined by the quantity of \({{\rm{H}}_{\rm{3}}}{{\rm{O}}^{\rm{ + }}}\) ions in the solution. Indicators are weak acids that have one colour for their acid state and another for their conjugate base.
• The indicator must be carefully chosen to ensure that the endpoint of the titration, when the indicator changes colour, nearly matches the reaction’s equivalence point.
• The addition of a very small volume of strong base results in a substantial shift in \({\rm{pH}}\) at the endpoint. The equivalency point for a reaction between a strong acid and a strong base is close to \({\rm{pH\,7}}\).
• There is a much more gradual shift in \({\rm{pH}}\) around the endpoint when a weak base is titrated with a strong acid, or a strong base is titrated with a weak acid.
  The indicators whose colour changes within the endpoint range can be used in this case.
• The \({\rm{pH}}\) shift in reactions involving weak acids and weak bases is so slow that a simple, direct titration cannot determine this combination. To find the equivalency point, we use tools like a \({\rm{pH}}\) metre.

What is Volumetric Weight?

Not all weight is created equal. It is more expensive to ship a plane full of feather pillows than it is to ship a plane full of iPhones. The pillows take up more room, cost less, and require more shipments to generate a profit.

Volumetric weight, also known as dimensional weight—is a pricing technique used by shipping companies to ensure that they don’t suffer a loss on large, lightweight shipments like pillows. The length, breadth, and height of the package are used to compute the volumetric weight. As a result, a big box of pillows could be regarded heavier than a small box of cellphones.

Measure the box’s length, breadth, and height to get its volumetric weight. The cubic size of your package is then calculated by multiplying the results.

Here’s an illustration: Assume you have a \({\rm{40\,inches}} \times {\rm{16\,inches}} \times {\rm{16\,inches}}\). When you multiply the three dimensions together — \(40 \times 16 \times 16\) — you get \(10,240\) cubic inches. 

Depending on the carrier, you’ll divide the total cubic inches by the dimensional weight divisor.

Summary

A widely used quantitative analytical method is volumetric analysis. As the name implies, this approach entails determining the concentration of the analyte by measuring the volume of a solution of known concentration. This is accomplished by determining the volume of a standard solution of an appropriate reagent with a known concentration. The reaction between the titrant solution and the analyte, commonly known as the titrant, is the basis of the procedure. The most popular method for performing this technique is to place the unknown solution in an Erlenmeyer flask and then slowly add the titrant to it with a burette. Titration is the name for this method.

FAQs

Q.1. What are the basic principles of volumetric analysis?
Ans: The basic principle of Volumetric analysis is that the solution we want to analyse contains a chemical of an unknown amount. The reagent reacts with that chemical of an unknown amount in the presence of an indicator to show the endpoint. Endpoint shows that the reaction is complete.

Q.2. What are the 4 types of titration?
Ans: Types of Titration are as follows:
• Acid-base Titrations
• Redox Titrations
• Precipitation Titrations
• Complexometric Titrations

Q.3. What is the endpoint in titration?
Ans: The endpoint of the titration is when an indicator indicates that all of the reactants required for a complete reaction have been added to the solution.

Q.4. What is the difference between endpoint and equivalence point?
Ans: The primary difference between equivalence and endpoint is that the former refers to the point at which a chemical process comes to a stop, whilst the latter refers to the point at which a system’s colour changes.

Q.5. What happens when the endpoint is reached?
Ans: The equivalence point is the ideal point for completing the titration. The equivalence point is often demonstrated by some type of indicator at the endpoint. As a colour indicator is used, for example, the solution changes colour when the titration reaches its endpoint.

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