Chemistry (Part-2) (CDS-Solved Paper)

Heating of a platinum crucible is a physical change. In a physical change, a substance undergoes a change in its physical properties such as shape, size, colour etc.
Physical changes are used to separate mixtures into their component compounds, but cannot be used to separate compounds into chemical elements or simpler compounds. In such a change no new substance is formed.
Examples of physical properties include melting, transition to a  gas, change of strength, change of  durability, changes to crystal form, textural change, shape, size, colour, volume and density.

Distilled water has a neutral pH that is neither alkaline nor acidic. This is because the number of hydroxyl ions and hydrogen ions in pure water is balanced. Pure water has a pH of 7.0 at 25°C.
As temperature increases, pH decreases. But, that does not mean that the water has become acidic. Here, the point at which pH is neutral drop. It is still neutral because the hydrogen ions and the hydroxyl ions in the water are still balanced.

The most important characteristic of a chemical element is its atomic number. It is equal to the number of protons in the nucleus of an atom of the element, and it is also equal to the number of electrons in the atom. The atomic number is the most important factor that determines the chemical properties of an element.

Isobars are atoms (nuclides) of different chemical elements that have same number of nucleons or mass number but different-atomic number such as ⁴⁰Ca, ⁴⁰Ar.

JJ Thomson, who discovered the electron in 1897, proposed the Plum pudding model of the atom in 1904 before the discovery of the atomic nucleus in order to include the electron in the atomic model. He proposed that an atom consists of a positively charged sphere and the electrons are embedded into it.

Avogadro’s number is a very important relationship in stoichiometric calculations : 1 mole = × 6.022 × 10²³. atoms, molecules, protons, etc.

To convert moles into atoms, multiply the molar amount by Avogadro’s number. To convert atoms into moles, divide the amount of atom by Avogadro’s number (or multiply by its reciprocal). Here, 1g of Na = 23 g. then number of atom in 46 g of ²³Na = 46.(N/23) = 2N

There are five states of matter-solids, liquids, gases, plasma and Bose-Einstein condensates. They exist due to difference in structures of each state and in densities of the particles.

The chemical properties of an element depend upon the number of electrons in the outermost shell of the element because they participate in bond formation and dissociation.

Normality is a way of expressing the concentration of solution. It is defined as the concentration expressed as the number of equivalent weights of solute per litre of solution.
● Here, equivalent weight of H₂SO₄ is 98/2 = 49.
● So, normality of solution is 1. Hence, the strength of 49 g of acid dissolved in water to make one litre of solution is 1N.

Allotropy is the property of some chemical elements to exist in two or more different forms, or allotropes, when found in nature. There are several allotropes of carbon, such as; coal, diamond, graphite, amorphous carbon, fullerenes and nanotubes, glassy carbon and carbon nanofoam