If you’ve ever used a pregnancy test, a blood glucose test kit, or a coronavirus rapid test kit at home, then you’ve already used reagents. Technically, the reagent that you use in home test kits are your own body fluids. Usually, this is in the form of either urine or blood, since these are needed in order for test kits to work.
However, a reagent is more broadly defined as any substance or compound that has been added to a system to trigger a chemical reaction. In this article, we’ll discuss the various aspects and applications of reagents.
In this post:
What Is A Reagent In Chemistry?
In terms of chemical classifications, a reagent is any organic or inorganic substance that can be added to a mixture to trigger a chain of chemical reactions. It’s also used to test for the presence of other substances in a solution. This makes certain types of reagents very useful as testing tools in experiments.
The term ‘reagent’ is usually used interchangeably with the term ‘reactant’, but the two have different and precise definitions: a reactant is consumed during a chemical reaction, while a reagent is not.
For example, solvents are used to dissolve chemicals, but they usually don’t participate in chemical reactions. Similarly, in biochemical reactions, especially those that involve catalytic enzymes, the reactants are called substrates, while the reagents are called catalysts.
Key Takeaways
A reagent is a substance that triggers a chemical reaction
Reagents can be used in testing, to detect the presence of certain chemicals, and in diagnostics
There are several types of reagents, and they can either be organic or inorganic, and solid or liquid
Some of the most common types of reagents are Collins reagent, Grignard Fenton’s reagent, Benedict’s reagent, and Tollens’ reagent
Reagent kits are chemical testing kits that can be used either in the laboratory or in the field. They’re commonly used to detect illicit drugs
Definition and Role of Reagents in Chemical Reactions
A reagent is a chemical that starts or limits chemical reactions. Unlike catalysts, they participate in chemical reactions. That means reagents are also reactants because they react to specific types or functional groups. This makes them excellent in detecting the presence of certain substances.
Reagents can also consistently convert certain types of chemicals into desired products. For example, Collins reagent converts alcohols into aldehydes or ketones through oxidation.
What Are Some Examples Of Reagents?
When used in organic chemistry, the term reagent means a type of chemical ingredient that is added to an organic mixture or solution in order to transform it into another type of substance. A reagent can be a compound or a mixture of organic or inorganic substances. Some common examples of reagents used in organic chemistry are:
- Collins reagent: This reagent is a metal-pyridine complex – specifically, the complex of chromium(VI) oxide with pyridine in dichloromethane. It’s solid, red in colour, and has a primary use of converting alcohols to aldehydes and ketones. It’s very useful in the oxidation of compounds that are sensitive to acids.
- Fenton’s reagent: This is a solution of hydrogen peroxide mixed with ferrous iron, like iron (II) sulphate. It’s a catalyst that’s used mainly to oxidise contaminants in waste waters. For example, it can neutralise and destroy toxic organic compounds like trichloroethylene and tetrachloroethylene.
- Grignard reagents: This group of reagents has a generic formula of R-Mg-X, where the X represents a halogen and the R represents an organic group of molecules. Typically, the R is an alkyl or aryl. The most common example of a reagent in this group is methylmagnesium chloride. Grignard reagents are commonly used to create new carbon bonds.
In terms of analytical chemistry, reagents are used to determine the presence or absence of another type of substance. Change in colour is the usual indicator. The concentration can be estimated by the degree of colour change. Some examples of these reagents are the following:
- Fehling’s reagent: This is a reagent that’s useful in differentiating between two molecular functional groups: carbohydrates and ketones. It’s used as a test for reducing sugars and non-reducing sugars. As an analytical reagent, it’s used as a supplementary reagent to the Tollen’s reagent test.
- Tollen’s reagent: This is a mixture of three compounds dissolved in a solution, namely silver nitrate, ammonia, and a small amount of sodium hydroxide. The alkaline compound is important to maintain the necessary pH of the reagent. It’s useful in identifying molecular functional groups.
- Millon’s reagent: A few drops of this reagent can detect the presence of soluble proteins in a test solution. When this happens, the reagent turns reddish brown, or precipitates are formed, which indicate the presence of tyrosine residue.
Common Types of Reagents
Reagents can be classified into different categories based on their chemical composition and purpose. They can either be acidic or basic, and organic or inorganic. They can either be electrophile (accepts electron pairs) or nucleophile (donates electrons).
Reagents can also be classified based on their uses such as in biochemical assays, analytical chemistry, and pharmaceutical research, and can be categorised based on their level of purity, such as technical grade (lowest) or analytical grade (highest).
What Is A Reagent Kit?
Reagent kits are testing kits that can be used in the field or in the lab to detect certain substances. They’re commonly used to test for the use of illicit drugs. Reagent test kits are typically simple to use, and usually involve colour changes when specific substances have been detected. Some testing kits are a little more complicated, and need to be processed in the laboratory using thin chromatography techniques.
Some examples of commonly used reagent kits are:
- Mandelin reagent kits: These are used to detect alkaloids and other compounds. The reagent turns dark green if amphetamine is present in a test solution, and a deep orange when cocaine is present.
- Marquis reagent kits: These are very useful in simple spot tests, where the reagent can detect a wide range of illicit drugs. For instance, it turns olive black in a test solution containing LSD. It’s also good in detecting methamphetamine, which makes it turn orange or brown.
- Mecke reagent kits: These are also used in simple spot tests. When mixed with a solution containing the psychedelic drug, like MDA, the reagent turns very dark blue. In the presence of heroin, it turns a deep bluish green.
- Froehde reagent kits: These are good at detecting some opioids and alkaloids, such as 2-CB, codeine, and ecstasy. In the presence of these drugs, the reagent turns yellow, dark green, red brown, and black with greenish brown, respectively.
What Is A Limiting Reagent In Chemistry?
As the name suggests, a limiting reagent is a reagent that limits or stops a chemical reaction when it’s completely consumed. This means that the chemical reaction cannot go any further because no more substance is available for the reaction to continue. Therefore, a limiting reagent determines when the reaction stops.
You can actually calculate the amount of reactants needed to complete a chemical reaction. If one of the reactants or reagents is exhausted, the reaction will stop at a certain point, leaving behind excess reactants. The stoichiometry of a reaction, which is simply the proportions of the reactants as indicated in the balanced equation, can be established with precision. You can calculate this by determining the respective mole proportions of the reactants. You can also measure the weight of the final products to determine the limiting reagent.
The Importance of Reagents in Scientific Research and Industry
Many scientific experiments are performed with the use of reagents. Reagents can be calibrated and made precise for each test, allowing experiments to be consistently repeatable and predictable.
For example, you can use a diagnostic reagent containing Tollen’s reagent to detect the presence of certain molecular functional groups in a mixture, and that can help to reverse engineer the chemical compositions of samples.
In chemical manufacturing, reagents are used as precursors, such as in the manufacture of different types of polymers.
Applications in Pharmaceuticals, Diagnostics, and Research
Pharmaceutical products, especially medicines, rely on the specificity of molecules to target certain receptors to be effective.
For example, a particular type of hypertension medicines called beta-blockers, block the receptors of hormones like adrenaline and noradrenaline in the cells of the heart to slow down its beat.
To design medicines, reagents cut, reposition, and connect functional molecular groups in certain ways. Many diagnostic kits, such as those used to detect COVID-19 and pregnancy, rely on the natural reagents produced by the body to indicate the presence of specific molecular markers in the blood, urine, or any other body fluids.
Medical and biochemical research relies on reagents as indicators of certain types of chemicals. Research in these fields would be very difficult without reagents that could indicate the start or end of certain biochemical reactions, such as in the formation of proteins, where Millon’s reagent is commonly used to detect proteins in a solution.
Conclusion
Reagents are substances that can start a reaction, limit a reaction, or determine the threshold of certain reactions. They can be calibrated to produce specific results. Reagents are very useful as chemical indicators. They can be classified into different categories and have a wide range of applications in chemistry, medicine, and in industries.
