Chemistry MCQs

Notes:
Iodoform is the organoiodine compound with the formula CHI3. A pale yellow, crystalline, volatile substance, it has a penetrating odor and, analogous to chloroform, sweetish taste. It is occasionally used as a disinfectant. Adolf Hitler’s mother, Klara Hitler, died of iodoform poisoning brought on by her treatment for breast cancer.

Notes:
In quantum chromodynamics, nucleons are regarded as composites of three quarks (elementary particles) and pions are composites of two quarks. According to EOB’s rules, nucleons move as fermions while pions move as bosons.

Notes:
The atomic radius is the distance from the atomic nucleus to the outermost stable electron orbital in an atom that is at equilibrium. It tends to decrease across a period from left to right with increasing number of valence electron. It usually increases while going down a group due to the addition of a new energy level (shell).

Notes:
Ice is not a mixture because the atoms in the ice are locked in a crystalline matrix whose atoms are less densely packed than those in the liquid water, a unique property of water.

Notes:
Silicon is a chemical element with the symbol Si and atomic number 14. Over 90 percent of the Earth’s crust is composed of silicate minerals. Highly purified silicon is used in semiconductor electronics in manufacturing microships.

Notes:
The metallic character of an element decreases while moving from left to right or bottom to top of the periodic table. This is because atoms have a better ability to gain electrons to fill a valence shell than lose them to and an unfilled shell. Metallic character is dependent on an element’s ability to lose its valence electrons.

Notes:
Rn is the symbol of Radon, a radioactive, colorless, odorless, tasteless noble gas. Radon itself is the immediate decay product of radium. Its most stable isotope, 222Rn, has a half-life of only 3.8 days, making radon one of the rarest elements since it decays away so quickly.

Notes:
Hydrogen sulfide (H2S) is a colourless gas with a characteristic odour of rotten eggs. It is often produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion.

Notes:
Coal is often called the “buried sunshine” because it developed from the remains of plants and greens that existed as long as 400 million years ago.

• Most of coal was formed 300 million years ago, when much of Earth was covered in “steamy swamps.”
• As these greens died, they fell to the bottom of the floor, forming peat.
• The coalification process (transformation into coal) begins when the peat is physically and chemically altered.

Notes:
Sodium bicarbonate and organic acid (Formic acid, Acetic acid, Carbonic acid, etc) react vigorously to liberate carbon dioxide. For example, Sodium bicarbonate (NaHCO3) when treated with acetic acid reacts vigorously to liberate carbon dioxide.

• NaHCO3 + CH3COOH —> CH3COONa + H2O + CO2