Chemistry MCQs

Notes:
Calcium carbide is also used in some countries for artificially ripening fruit. When calcium carbide comes in contact with moisture, it produces acetylene gas, which is quite similar in its effects to the natural ripening agent, ethylene. Acetylene acts like ethylene and accelerates the ripening process.

Notes:
Zirconium purified metal is primarily used by the nuclear industry to form the outer layer of fuel rods in nuclear reactors. Zirconium’s major use is as cladding for nuclear reactors. It is ideal for this use, as it has a limited ability to capture neutrons, strength at elevated temperatures, considerable corrosion resistance, and satisfactory neutron damage resistance.

Notes:
In 1828, Friedrich Wöhler artificially synthesized urea by heating ammonium cyanate. This experiment was the first to produce an organic compound from inorganic precursors. The synthesis challenged the theory of vitalism, which claimed that organic compounds could only be created by living organisms. Urea has the chemical formula CO(NH2)2 and is a major component of human urine.

Notes:
J.J. Thomson proposed his atomic model soon after his discovery of electrons. Its major postulates were: (1) An atom contains negatively charged particles called electrons embedded uniformly throughout a thinly spread positively charged mass. (2) Since the atom is electrically neutral, the total negative charge of electrons is balanced by the total positive charge. Thomson’s model of an atom is popularly known as plum pudding model or apple pie model or watermelon model. Thomson’s model could successfully explain the electrical neutrality of atom. However, it failed to explain how the positively charged particles are shielded from the negatively charged electrons without getting neutralized.

Notes:
The pH of fresh milk is 6, to set it as curd needs the pH below 6. In order to avoid this, the milkman shifts the pH of fresh milk from 6 to slightly alkaline by adding baking soda. Since, the milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base added. Therefore, it takes longer time for the curd to set.

Notes:
Isotopes of an element have similar chemical properties as they have the same number of electrons as an atom of that element. The electron arrangement is the same owing to same chemical properties. However, they have different numbers of neutrons, which affects the mass number. Mass number determines the physical properties such as boiling/ melting/ density etc.

Notes:
J. J. Thomson discovered a negatively charged particle, called the electron. The alpha particle is nothing but positively charged helium nuclei, it has charge of two time of that of the proton, as it is constituted of two protons.

Notes:
The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden gold foil experiment. Protons and neutrons are bound together to form a nucleus by the nuclear force.

Notes:
Mass number is the sum of the numbers of protons and neutrons present in the nucleus of an atom. The mass number is different for each different isotope of a chemical element. This is not the same as the atomic number (Z) which denotes the number of protons in a nucleus, and thus uniquely identifies an element.

Notes:
For large scale production of oxygen either air is distilled or water is electrolysed. KMnO4 is used for laboratory praporation while MnO2 is used as a catalyst nor source of oxygen.

• 2H2O2 —(MnO2)>  2H2O + O2 [upward arrow]