Chemistry Glossary

Addition polymers

In an addition reaction, two unsaturated monomers combine to form addition polymers, without the elimination of atoms. Examples of such polymers are high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polyvinyl chloride (PVC). 

Alcohols

Alcohols are a class of organic compounds characterized by the presence of a hydroxyl group (-OH) attached to a carbon atom. This functional group is responsible for the properties and reactivity of alcohols, making them an essential category in organic chemistry. Alcohols can range from simple molecules like methanol (CH₃OH) to more complex structures, and they are widely used in various industries, from pharmaceuticals to beverages. 

Back Titration

Back titration is a two-step analytical technique used to determine the concentration of an analyte when direct titration is not feasible. In this method, an excess of a known reactant is added to the analyte. The remaining, unreacted portion of the reactant is then titrated with another reagent. By measuring how much of the excess reactant remains, the concentration of the analyte can be calculated. This method is especially useful for analyzing substances that are not easily titrated directly or when the reaction between the analyte and the reactant is slow.

Biofuels

 Biofuels are fuels derived from biomass, which consists of biological material from living or recently living organisms. There are three main types of biofuels:

• Bioethanol: A type of ethanol produced through the fermentation of monosaccharides, such as glucose and fructose.

• Biogas: A mixture of gases, including methane, carbon monoxide, and hydrogen, released during the natural breakdown of organic matter by anaerobic bacteria.

• Biodiesel: A liquid fuel composed of long hydrocarbon chain esters, typically produced from vegetable oils or animal fats.

Chromophore

A chromophore is a structural fragment of a molecule that absorbs specific wavelengths of light, leading to the characteristic color of the compound. Different functional groups within the chromophore absorb light at different wavelengths:

• The carboxyl group (–COOH) absorbs infrared (IR) light at 1660 cm⁻¹ and 2900 cm⁻¹.

• The benzene ring absorbs ultraviolet (UV) light at 266 nm.

• The amino group (–NH₂) absorbs infrared (IR) light at 3450 cm⁻¹.

Colourimetry

Colourimetry is an analytical technique used to determine the concentration of a colored substance in a solution by measuring its absorbance of light.

This technique is based on the principle of the Beer-Lambert law, which states that the absorbance of light is directly proportional to the concentration of the analyte in the sample. Mathematically, this is expressed as A=ϵlcA = \epsilon lcA=ϵlc, where:

• A is the absorbance,

• ϵ is the molar absorptivity,

• l is the path length of the light through the sample, and

• c is the concentration of the analyte.

By using a colorimeter to measure the absorbance of light, we can accurately determine the concentration of the colored solution.

Schematic for a Colourimeter:

• Lamp: Provides the light source.

• Slit: Narrows the beam of light.

• Coloured Filter: Selects the specific wavelength of light that is absorbed by the analyte.

• Sample: The solution containing the analyte whose concentration is to be measured.

• Detector: Measures the amount of light that passes through the sample.

Density

Density is defined as the mass of a substance per unit volume. It is mathematically represented by the formula:

d=m/v

where:

• d is the density,

• m is the mass of the substance, and

• v is the volume of the substance.

The units for density are typically expressed as grams per milliliter (g/mL) or grams per cubic centimeter (g/cm³).

Dispersion Forces

Dispersion forces are attractive forces that arise between atoms and molecules due to the presence of temporary, fluctuating dipoles. These dipoles occur when the electron distribution within atoms or molecules momentarily becomes uneven, causing a temporary polarity. Dispersion forces are significant when atoms or molecules are very close together. 

Effervescence

Effervescence is the formation of bubbles in a liquid, typically indicating that a chemical reaction has occurred, releasing gas as a product. 

Ester

Esters are organic compounds characterized by the functional group (−COO−)(-COO-)(−COO−).

They are formed through an esterification reaction, which occurs between a carboxylic acid and an alcohol. In this reaction, the hydroxyl group (−OH)(-OH)(−OH) of the carboxylic acid is replaced by the alkoxy group (−OR)(-OR)(−OR) from the alcohol, resulting in the formation of an ester.

Fermentation

Fermentation is a biochemical process that converts carbohydrates into simple alcohols and carbon dioxide through the action of enzymes (biological catalysts) produced by microorganisms such as yeast and bacteria.

Example of the fermentation of glucose to produce ethanol:

glucose→ethanol+carbon dioxide

C6​H12​O6​(aq)→2C2​H5​OH(aq)+2CO2​(g)

The four conditions necessary for this fermentation process are:

• Presence of the enzyme zymase (found in yeast)

• Warm temperatures (30–40 °C)

• Anaerobic environment (absence of oxygen)

• Aqueous solution of sugar

Gravimetric Analysis

Gravimetric analysis is a quantitative analytical technique that quantifies an analyte by measuring the mass of a product formed through a precipitation reaction.

Steps in Gravimetric Analysis:

1. A known quantity of the sample is dissolved in water.

2. The analyte is precipitated from the solution using a suitable reagent.

3. The precipitate is collected by filtration, washed, dried, and weighed.

Hydrogen Bonding

Hydrogen bonding is a strong intermolecular interaction that occurs due to the high electronegativity of fluorine, oxygen, and nitrogen, combined with the electropositivity of hydrogen. These atoms can interact to form hydrogen bonds, often abbreviated as H-bonding.

Conditions for Hydrogen Bonding:

• Hydrogen atoms must be bonded to nitrogen, oxygen, or fluorine atoms within a molecule.

• There must be a non-bonding (lone) electron pair on a nitrogen, oxygen, or fluorine atom in an adjacent molecule.

Hygroscopic

Hygroscopic substances are materials that absorb moisture from the air, which can cause their weight to change during weighing. Due to this property, hygroscopic substances are not suitable for use as primary standards in preparations. Examples of such substances include sodium hydroxide (NaOH) and potassium hydroxide (KOH). 

Indicators

Indicators provide a qualitative measure of the concentration of hydrogen ions in a solution. Most indicators are weak acids or bases, creating an equilibrium between their two forms.

Isotopes

Isotopes are variants of a chemical element that have the same atomic number (number of protons) but differ in the number of neutrons. This difference in neutron count results in different mass numbers (sum of protons and neutrons) for the isotopes of the same element. 

Ketone

Ketones are organic compounds characterized by the presence of a carbonyl functional group located in the middle of a carbon chain. The carbonyl functional group consists of a carbon atom double-bonded to an oxygen atom, represented as C=O. 

Markovnikov’s Rule

Markovnikov’s rule states that in addition reactions involving unsymmetrical alkenes, the hydrogen atom will predominantly attach to the carbon atom that already has the greater number of hydrogen atoms.

This rule is useful for predicting the major and minor products formed when asymmetric reagents, such as HBr, react with an asymmetric alkene.

Molecular Formula

The molecular formula provides the exact number of atoms of each element present in a molecule or compound. 

Parallax Error

Parallax error occurs when an object is viewed from a different angle, leading to a different measurement. To avoid parallax error, ensure that all measurements are taken at eye level. 

Pipette

A pipette is a piece of glassware used to transfer a very precisely measured volume of solution. Pipettes used in titration are calibrated to deliver the exact volume of solution without applying additional force. Therefore, any liquid remaining on the tip of the pipette should not be shaken or blown out. 

Solute

A solute is a substance, typically a solid, that dissolves in a solvent to form a solution. 

Solubility

Solubility refers to the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature. 

Titrand

The titrand is the solution to which another reagent, known as the titrant, is added during a titration. This process typically takes place in a conical flask. 

Titrant

The titrant is the solution that is added during a titration, usually from a burette. 

Titration

Titration is an analytical technique used to determine the quantity of a substance (known as an analyte) present in a sample by measuring its moles. The necessary equipment for performing a titration is depicted below. 

Viscosity

Viscosity describes a substance’s resistance to fluid flow. Liquids that exhibit a relatively high resistance to flow are said to have high viscosity. For instance, honey has a relatively high viscosity. 

Volumetric Flask

A volumetric flask is a piece of glassware designed to hold a precise volume of solution with high accuracy. It is commonly used in the preparation of standard solutions. 

Yield

The yield of a reaction is the amount of product obtained, expressed as a percentage of the theoretical maximum possible yield.