Quantitative and qualitative analysis are the two main types of methods used in chemistry to determine the chemical makeup of a material. When comparing qualitative and quantitative research, the main distinction in chemistry is that while the former determines the presence or absence of specific chemical components, the latter measures how much of such components are present in a given sample.
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Quantitative Analysis
Quantitative analysis is the branch of chemistry concerned with determining how much of each component there is in a given sample. The value can be written in a variety of units, including mass, volume, concentration, and relative abundance.
There are two methods in quantitative analysis which are:
• Chemical methods – Chemical methods include titration methods, gravimetric methods, combustion analysis techniques, and chemical reactions (for example, oxidation, reduction, precipitation, neutralization, and so on).
• Physical methods – Physical methods examine one or more of a sample’s physical attributes. AES (Atomic emission spectroscopy), x-ray fluorescence spectroscopy, mass spectroscopy, and other techniques are examples.
Why it is important to conduct Quantitative analysis?
The importance of quantitative analysis on a sample cannot be overstated for a number of compelling reasons. To reduce chemical waste and maximize atom economy, this method calculates how much of each reactant is needed to complete a chemical synthesis process and produce the desired amount of product. Indicating the presence of adequate amounts of substances, and judging the purity of a sample, it can also be used to evaluate the quality of food or other products.
In this article, we will go over two crucial methods of quantitative analysis:
- Volumetric Analysis
- Gravimetric Analysis
Volumetric Analysis
Quantitative methods of analysis include volumetric analysis, which involves determining the concentration of a chemical in a solution by reacting a known volume of the solution with a solution of the material at a known concentration.
According to the law of chemical equivalence, substances react in the same ratio as their equivalent weight. This is the foundation of volumetric analysis. ‘Titration’ refers to the method used to do this kind of analysis.
Conditions for Volumetric Analysis
The reaction involved in volumetric analysis must satisfy the following requirements.
• The reaction must be stoichiometric.
• Reaction should be fast.
• Reaction must be specific and there should be no side reaction.
• Reaction must show a sharp color change at the end of the reaction.
Titration
Titration, also called titrimetry, is a method of chemical qualitative analysis that can be used to determine how much of a specific analyte is present in a sample. Titration, commonly known as volumetric analysis, is a vital procedure in the science of analytical chemistry.
Types of Titrations
Depending on the types of reactions involved, titrations can be classified as follows:
• Acid-base Titration
• Redox Titrations
• Precipitation Titration
• Complexometric Titration
Acid-Base Titration
Titration with acids and bases, also called acidimetry or alkalimetry, is a technique used in chemistry for making this determination. When an acid and a base are mixed in a solution, neutralization takes place. This is the primary mechanism upon which acid-base titrations depend. The concentration of an acid can be calculated using a standard base solution. Acidimetry is another name for this method.
The amount of H+ ions (hydrogen ions) an acid dissociates into in water is a good indicator of how powerful or weak it is. Assuming the neutralization reaction proceeds to completion, the concentration of an acid solution can be calculated by titrating it with a strong base of known concentration. For the same reason, a strong base is needed throughout the titration procedure. Therefore, the strong base is the standard solution, and the acid solution is the titrate, in this case.
Acids can be categorized as either strong or weak based on their level of dissociation in water, which determines the amount of H+ ions they release. The concentration of an acid solution can be determined by titrating it with a strong base of known concentration, assuming that the neutralization reaction goes to completion. The titration process requires the use of a strong base for the same reason. So the acid solution is the titrate in this situation, and the strong base is the titrant or standard solution
Acid is titrated with a base and base is titrated with an acid. The endpoint is usually detected by adding an indicator.
For Example:
HA + BOH → BA + H2O
where,
• HA is acid and A is a negative ion
• BOH is base and B positive ion
Redox Titration
As the name suggests this Titration is an example of an oxidation-reduction reaction. This titration relies on electron transport among the reactive ions in aqueous solutions to produce the chemical reaction. Redox titration involves two solutions, one of which acts as a reducing agent and the other as an oxidizing agent. The purpose of this experiment is to determine the strength of the oxidizing or reducing agent. Due to the complexity of maintaining a constant redox potential, we typically favor the equivalency idea. Titration of redox couples can be broken down even further according to the reagent employed. Some of them are listed below.
- Permanganate Titration
- Dichromate Titration
- Iodimetric and Iodometric Titration
Permanganate titration
Permanganate titration is a method used in analytical chemistry to determine the concentration of a substance by adding a solution of permanganate
Potassium permanganate serves as an oxidizing agent. The item is maintained in good condition through the use of dilute sulphuric acid.
The balanced equation for the reaction is:
MnO4– + 8H+ + 5e– → Mn2+ + 4H2O
This solution is colorless until the endpoint. In addition, potassium permanganate is utilized for the determination of oxalic acid, ferrous salts, hydrogen peroxide, oxalates, and various other substances.
Dichromate titration is a method used in analytical chemistry to determine the concentration of a substance in a solution.
Potassium dichromate is commonly utilized as an oxidizing agent in acidic environments. In addition, the acidic environment is sustained through the use of diluted sulphuric acid.
The balanced chemical equation for the reaction between K2Cr2O7 and H2SO4 is:
K2Cr2O7 + H2SO4→ K2Cr2SO4 + H2O + 6O
Iodometric Titration
Iodimetric and iodometric titrations are two commonly used analytical techniques in chemistry.
In this titration, iodine or iodine solution is utilized as the titrant. Iodine is utilized in two different ways in these titrations: Iodometric titration is a method used in analytical chemistry to determine the concentration of a substance by measuring the amount of iodine.
In Iodometric Titration, the I2 molecule is utilized as a titrant to determine the concentration of a reducing agent in a solution whose concentration is unknown. In this process, I2 is converted into an iodide ion. Below is the description of the reaction.
In Iodometric Titration, the I– molecule is utilized as a titrant to determine the concentration of an unknown oxidizing agent in a solution. In this process, the element I is converted into a molecule of iodine. The following reaction is mentioned below.
The equation 2l– → I2 + 2e– represents the process of oxidation.
Precipitation Titration
This titration method relies on the formation of a precipitate. During precipitation titration, two chemicals that react with each other are brought into contact. For instance, when utilizing silver nitrate solution, one may employ either ammonium thiocyanate or sodium chloride solution. When it undergoes interaction, it results in the formation of a white precipitate composed of either silver thiocyanate or silver chloride.
The chemical equation is as follows:
AgNO3 + NaCl → AgCl + NaNO3
The titration is commonly followed by Gravimetric Analysis to determine the concentration of ions in the precipitate.
Complexometric Titration
Complexometric titration is a technique used in analytical chemistry to determine the concentration of a metal ion in a solution. It involves the formation
The most significant occurrence in this titration is the development of an undissociated compound. It encompasses more than just precipitation titrations. For example:
The reaction can be represented as follows:
Hg2+ + 2SCN–→ Hg(SCN)2
EDTA, also known as ethylenediaminetetraacetic acid, is a crucial reagent used to form compounds with metals.
Gravimetric Analysis
Gravimetric analysis is an analytical technique that is used to quantitatively determine an analyte by measuring the mass of a solid substance. In this method of analysis, the element to be identified is precipitated from a solution by adding a suitable precipitating agent. The precipitate should either possess a known composition or be transformed into another compound with a known composition through heating.
The requirements for gravimetric analysis are as follows:
- For successful gravimetric analysis using the precipitation method, it is essential to meet the following fundamental condition.
- The component that requires estimation should be completely precipitated.
- The precipitate must be pure before it is weighed.
- The precipitate should be appropriate for various handling tasks, such as filtering, washing, and weighing.
- The selection of an insoluble precipitate of the constituent to be determined is the most fundamental requirement for gravimetric analysis. This precipitate should have sufficient stability and be suitable for manipulation.
Principle of Gravimetric Analysis
Gravimetric Analysis is a method that relies on the principle that the mass of an ion in a pure compound can be determined by calculating the mass percentage of the same ion in a known quantity of an impure compound.
Preparing a solution
The sample was carefully weighed on a watch glass and then transferred to a beaker. If the salt sample is soluble in water, it is dissolved in water to create a solution. Insoluble salts can be dissolved in dilute acids. Once the sample has completely dissolved, additional water can be added to achieve the desired volume of the solution.
Precipitation
Precipitation is a term used to describe the process of water falling from the atmosphere to the Earth’s surface. The sample solution is heated before adding the appropriate precipitant slowly and in slight excess, while continuously stirring the solution. The solution containing the precipitate is then heated and left to stand for a period of time. The precipitate is given time to settle. To ensure complete precipitation, a few drops of precipitant are added to the supernatant liquid and checked.
Filtration and Washing of Precipitate
Pour the precipitate into the funnel and proceed to wash it using the appropriate wash solution. In order to ensure the high purity of the precipitate, it is important to check the washing process using appropriate reagents like AgNO3 solution and BaCl2.
Drying Process
A crumpled piece of paper is placed over the rim of the funnel to cover the purified precipitate inside. The funnel containing the precipitate is then placed in a hot air oven to dry.
Ignition
Once the filter paper with the precipitate is fully dried, it is carefully removed from the funnel and folded to completely enclose the precipitate. The packet is placed in the weighted crucible, which is securely held in place by the clay pipe triangular tripod stand. The crucible is initially heated at a slow pace. Once all the moisture has been completely removed, the flame is intensified in order to carbonize the paper. The crucible is fully heated when the paper is completely carbonized. Once all of the carbon has been removed, the crucible is covered with a lid. The ignition process typically takes around 50-60 minutes to complete.
Heating until a constant weight is achieved
After the ignition process is complete, the flame is extinguished and the crucible is placed inside the desiccators. It is then left to cool for a duration of 15 to 30 minutes. The crucible and lid are subsequently weighed together. Afterward, the crucible substance is reignited for approximately 10 minutes. It is then allowed to cool in desiccators, as mentioned before, and weighed once more. The process of lighting and weighing is repeated until a consistent weight is reached.
The weight of the precipitate can be determined by subtracting the weight of the crucible with its lid from the combined weight of the crucible content along with the lid.
References
- https://byjus.com/chemistry/gravimetric-analysis/
- https://www.britannica.com/science/volumetric-analysis
- https://byjus.com/chemistry/volumetric-analysis/
- https://scienceready.com.au/pages/gravimetric-analysis
- https://www.pharmaguideline.com/2021/10/principle-and-steps-involved-in-gravimetric-analysis.html
- https://snscourseware.org/snscphs/files/1577033608.pdf.
- https://www.vedantu.com/chemistry/gravimetric-analysis
