Chemistry MCQs

Notes:
Atomic number of a chemical element is the number of protons found in the nucleus of an atom of that element, and therefore identical to the charge number of the nucleus. It determines the position of an element in the modern periodic table. In an uncharged atom, the atomic number is also equal to the number of electrons.

Notes:
Valency is number of electrons gain or loss to achieve noble gas configuration I.e. fully filled octet. Magnesium (Atomic number = 12) has electronic configuration 2, 8, 2. Since magnesium has 2 electrons in its outermost shell, hence it’s valency is 2, i.e., it will lose it’s 2 electrons to achieve noble gas configuration (2,8).

Notes:
Atomic number is the number of protons present in an atom; while, mass number is the sum of the number of protons and the neutrons of an atom. Isotones are the atoms of different elements which contain same number of neutron with different mass number and atomic number. For example, Silicon and Phosphorous have same number of neutron 16 with different mass number 30,31 and atomic number 14,15.

Notes:
The iron displaces copper from its salt, to make iron sulfate solution and deposit a thin coating of metallic copper on the surface of the metal. In general, any metal higher than copper in the “electromotive series” will displace copper from copper sulfate solution or any other copper salt solution.

Notes:
When a pentavalent (donor) impurity, like arsenic, is added to germanium, it will form covalent bonds with the germanium atoms, leaving 1 electron relatively free in the crystal structure. Pure germanium may be converted into an n-type semiconductor by “doping” it with any donor impurity having 5 valence electrons in its outer shell. Semiconductors which are doped in this manner – either with N- or P-type impurities – are referred to as extrinsic semiconductors.

Notes:
Seaweed such as lamanaria, polysyphonia are rich sources of iodine, a trace element essential for healthy thyroid function and a healthy metabolism. Iodine is particularly vital for pregnant and lactating women. Seaweed also contains zinc and antioxidants, which help strengthen immunity.

Notes:
Concentrated nitric acid is a very strong oxidator capable of reacting with the noble metals such as copper or silver. Some precious metals, such as pure gold and platinum-group metals do not react with nitric acid. However, pure gold does react with aqua regia, a mixture of concentrated nitric acid and hydrochloric acid.

Notes:
In arc welding, Argon is used as a shielding gas because it is chemically inert and forms no compounds. At the high temperatures that welding requires, the metals being welded become highly reactive to the elements in the atmosphere. Contamination from these elements can lead to brittle welds and instability in the welding arc. So,argon and other inert gases are sprayed.

Notes:
When we leave a piece of iron in the open for some time, it acquires a film of brownish substance. This substance is called rust and the process is called rusting. Iron gates of parks or farmlands, iron benches kept in lawns and gardens, almost every article of iron, kept in the open gets rusted.

Notes:
Catenation is the binding of an element to itself through covalent bonds to form chain or ring molecules. Carbon is the most common element that exhibits catenation. It can form long hydrocarbon chains and rings like benzene.