Chemistry MCQs

Notes:
Nitrogen is present in the environment in a wide variety of chemical forms including organic nitrogen, Ammonium (NH4+), nitrite (NO2–), nitrate (NO3–), nitrous oxide (N2O), Nitric oxide (NO) or inorganic nitrogen gas (N2). For organisms to use atmospheric nitrogen (N2), it must be “fixed” or converted into ammonia (NH3).The processes of the nitrogen cycle transform nitrogen from one form to another. It involves nitrification, the conversion of ammonia (NH3) to nitrate (NO3–). Ammonia does not contain oxygen.

Notes:
Borax (Na2B4O7.10H2O) is also known as Sodium borate or Sodium Tetraborate Decahydrate. It is an important boron compound, a mineral, and a salt of boric acid. Borax is a component of many detergents, cosmetics, and enamel glazes and is also used to make buffer solutions in biochemistry, as a fire retardant, as an anti-fungal compound, etc.

Notes:
Sodium carbonate (Na2CO3), also known as washing soda or soda ash, is used as a water softener in laundering. It competes with the magnesium and calcium ions in hard water and prevents them from bonding with the detergent being used. Sodium carbonate can be used to remove grease, oil, and wine stains. It is also used for removing the permanent hardness of water.

Notes:
The synthase enzyme converts the amino acids sulfoxides of the onion into sulfenic acid.

• The unstable sulfenic acid rearranges itself into synropanethial-S-oxide.
• Citric acid is a weak organic acid that occurs naturally in citrus fruits.
• Nitric acid is a highly corrosive mineral acid.
• Sulphuric acid is a mineral acid composed of the elements sulfur, oxygen and hydrogen.

Notes:
Detergents yields froth with both hard and soft water while soaps yield froth only with soft water not hard water.

Notes:
A catalyst is an agent or compound that increases the rate of a reaction without itself being consumed. Enzymes are naturally occurring catalysts responsible for many essential biochemical reactions. Most solid catalysts are metals or the oxides, sulfides, and halides of metallic elements and of the semi-metallic elements boron, aluminum, and silicon.

Notes:
Methanol (CH3OH) is also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits. It acquired the name “wood alcohol” because it was once produced chiefly as a byproduct of the destructive distillation of wood. Modern methanol is produced in a catalytic industrial process directly from carbon monoxide, carbon dioxide, and hydrogen.

Notes:
Water is not effective on petrol fire because it has higher density than petrol as a result of which it sinks to the bottom, while petrol stays afloat and keeps burning. Petrochemical fires are always extinguished with chemical foam which forms a in combustible blanket over the flames and cuts off the oxygen supply.

Notes:
Malic acid is a naturally occurring substance found in many fruits and vegetables, and is largely responsible for the sour taste found in apples and pears. Malic acid was first isolated from apple juice by Carl Wilhelm Scheele in 1785.

Notes:
Melting points and boiling points of some compounds of carbon :
(Compound) – (Melting point)(K) – (Boiling point)(K)

• Acetic acid – (CH3 COOH): 290, 391
• Chloroform – (CHCl3): 209, 334
• Ethanol – (CH3CH2OH): 156, 351
• Methane – (CH4): 90, 111