- Distillation – 01
- TYPES OF DISTILLATION
- SIMPLE DISTILLATION
- STEAM DISTILLATION
- FRACTIONAL DISTILLATION
- VACUUM DISTILLATION
- ATOMS & MOLECULES
- DALTON’S ATOMIC THEORY
- SALIENT FEATURES OF DALTON’S ATOMIC THEORY
- ATOMIC MASS
Distillation – 01
TYPES OF DISTILLATION
Types of distillation include
- Fractional Distillation(different volatile ‘fractions’ are collected as they are produced)
- Destructive Distillation (usually, a material is heated so that it decomposes into compounds for collection).
Simple distillation may be used when the boiling points of two liquids are significantly different from each other or to separate liquids from solids or nonvolatile components. In simple distillation, a mixture is heated to change the most volatile component from a liquid into vapor. The vapor rises and passes into a condenser. Usually, the condenser is cooled (e.g., by running cold water around it) to promote condensation of the vapor, which is collected.
Steam distillation is used to separate heat-sensitive components. Steam is added to the mixture, causing some of it to vaporize. This vapor is cooled and condensed into two liquid fractions. Sometimes the fractions are collected separately, or they may have different density values, so they separate on their own. An example is steam distillation of flowers to yield essential oil and a water-based distillate.
Fractional distillation is used when the boiling points of the components of a mixture are close to each other, as determined using Raoult’s law. A fractionating column is used to separate the components used a series of distillations called rectification. In fractional distillation, a mixture is heated so vapor rises and enters the fractionating column. As the vapor cools, it condenses on the packing material of the column. The heat of rising vapor causes this liquid to vaporize again, moving it along the column and eventually yielding a higher purity sample of the more volatile component of the mixture.
Vacuum distillation is used to separate components that have high boiling points. Lowering the pressure of the apparatus also lowers boiling points. Otherwise, the process is similar to other forms of distillation. Vacuum distillation is particularly useful when the normal boiling point exceeds the decomposition temperature of a compound.
Crystallization is defined as a process by which a chemical is converted from a liquid solution into a solid crystalline state. The widespread use of crystallization within industry is in part due to the fact that crystallization acts as both a separation and purification step. How does the crystallization process occur? The crystallization process consists of two major events:
- Nucleation – Molecules gather together in clusters in a defined manner. Clusters need to be stable under current experimental conditions to reach the “critical cluster size” or they will redissolve. It is this point in the crystallization process that defines the crystal structure.
- Crystal Growth – Nuclei that have successfully achieved the “critical cluster size” begin to increase in size. Crystal growth is a dynamic process, with atoms precipitating from solution and becoming redissolved. Supersaturation and supercooling are two of the most common driving forces behind crystal formation.
- In 1661, Robert Boyle was the first scientist who used the term element; Antoine Laurent Lavoisier, a French chemist, was the first who experimentally define the term element.
‘… Element is as a basic form of matter that cannot be broken down into simpler substances by a chemical reaction…. ”
- Elements normally can be categorized as
- A solid material, which typically is hard, ductile, malleable, shiny, and fusible with good electrical and thermal conductivity, is known as metal. E.g. Gold, Silver, Copper, Aluminum, etc.
- Approximately three-quarters of all known chemical elements are metals. The most abundant varieties in the Earth’s crust are aluminum, iron, calcium, sodium, potassium, and magnesium. The vast majority of metals are found in ores (mineral-bearing substances), but a few such as copper, gold, platinum, and silver frequently occur in the
- Metals differ widely in their chemical reactivity.
- Mercury is the only metal that remains liquid at room temperature.
- All elements or substances, which are not metals, are known as non-metals. E.g. Hydrogen, Oxygen, Iodine, Carbon, etc.
- Non-metals have variety of colors and they are poor conductors of heat and electricity.
- Non-metals are not lustrous, sonorous, or malleable.
- A substance, composed of two or more elements, is known as ‘compound.’
- Compound is the result of the chemically combination of two or more elements in a fixed proportion.
- Properties of a compound are somehow different from its constituent elements, whereas, the properties of a mixture are the same as of its constituting elements or compounds.
- Around 500 BC, an Indian Philosopher Maharishi Kanad, first time postulated the concept of indivisible part of matter and named it ‘pramanu.’
- In 1808, John Dalton used the term ‘atom’ and postulated the atomic theory to the study of matter.
- According to Dalton’s atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms.
- According to Dalton’s atomic theory, all matters, whether they are elements, compounds, or mixtures, are composed of small particles known as atoms.
- All matter is made of very miniscule particles known as atoms.
- Atom is an indivisible particle, which cannot be created or destroyed through chemical reaction.
- All atoms of an element are identical in mass and chemical properties whereas, atoms of different elements have different masses and chemical properties.
- To form a compound, atoms are combined in the ratio of small whole numbers.
- In a given compound, the relative number and kinds of atoms are constant.
- The mass of an atom of a chemical element; it is expressed in Atomic Mass Units (Symbol Is U).
- The atomic mass is roughly equivalent to the number of protons and neutrons present in the atom.
- “…..One atomic mass unit is a mass unit equal to the exactly one-twelfth (1/12th) the mass of one atom of carbon-12 and the relative atomic masses of all elements have been calculated with respect to an atom of carbon-12….”
- The smallest particle of an element or a compound, which is capable to exist independently and shows all the properties of the respective substance.
- A molecule, normally, is a group of two or more atoms which are chemically bonded together.
- Atoms of the same element or of different elements can join (with chemical bond) together to form molecules.
- The number of atoms that constitute a molecule is known as its atomicity.