Chemistry MCQs

Notes:
Copper is deposited at the cathode and is dissolved at the anode. Consequently the concentration of copper ions in solution remains constant. This can be used as a method of purification of copper as only pure copper is deposited at the cathode. Bubbles of gas (oxygen) are formed and evolved at the anode.

• Cathode reaction: Cu2+ + (aq) + 2e– —> Cu(s); and
• Anode reaction: 2H2O(l ) —> O2(g) + 4H+(aq) + 4e-

Notes:
Oxidized forms of nitrogen include nitrite (NO2) and nitrate (NO3). Nitrogen mainly occurs in wastewater in this form. Because nitrite is easily oxidized to nitrate, nitrate is the compound predominantly found in groundwater and surface waters.

• 4NH4O —> 4NH4(+) + 4OH(–)
• 4OH(–) —> 2H2O + O2
• NH4 + O2 —> NO2(–) + 2H2O
• 2NO2(–) + O2 —> 2NO3(–)

Notes:
The atomic radius is a measure of the size of an atom. It is defined as one-half the distance between the nuclei of two identical atoms that are bonded together. Angstrom is the most common unit used for measuring atomic radius. It is equivalent to 1 × 10(to the power –10) m. Under most definitions, the radii of isolated neutral atoms range between 30 and 300 pm (trillionths of a metre), or between 0.3 and 3 angstroms.

Notes:
Thorium is a radioactive chemical element found in nature as thorium-232. It is found primarily in the rare earth mineral monazite but can also be found in euxenite and thorianite. Thorium is found more abundantly in the Earth’s crust than uranium and only occurs naturally in an oxidized form.

Notes:
Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colourless, syrupy, sweet-tasting liquid. Due to its low freezing point ethylene glycol resists freezing. A mixture of 60% ethylene glycol and 40% water freezes at -45 degree C (-49 degree F).

Notes:
The foot of the common mussel (Mytilus edulis) produces a sticky glue due to a unique compound called mussel adhesive protein, which contains a high concentration of an amino acid, DOPA (dihydroxyphenylalanine), which can cling to wet surfaces with extraordinary strength. Besides heart implants, the compound is also used as a tooth coating to prevent dental plaque, which is caused by bacterial infection.

Notes:
Amines are organic derivatives of ammonia, in which one, two, or all three of the hydrogens of ammonia are replaced by organic groups. All aliphatic primary amines are stronger bases than ammonia. In aqueous solution, the pKb’s (basicity) of ammonia, methyl amine, dimethylamine, and trimethyl amine are therefore, respectively, 4.74, 3.34, 3.27. and 4.19. In terms of pKb, the strongest bases have the least positive values of pKb. So in aqueous solutions, the strongest bases are:

• Dimethylamine > Methylamine > trimethylamine > Ammonia.

Notes:
Phenol is also known as carbolic acid. It is an aromatic organic compound with the molecular formula C6H5OH. The molecule consists of a phenyl group (–C6H5) bonded to a hydroxyl group (–OH). It is primarily used to synthesize plastics and related materials.

Notes:
Ethyl acetate is a fruity smelling liquid with a brandy note and is the most common ester in fruits. It is the acetate ester formed between acetic acid and ethanol.It is found in alcoholic beverages, cereal crops, radishes, fruit juices, beer, wine, spirits, etc.

Notes:
A compound is organic if it contains carbon. A cyanide is a chemical compound that contains the group CºN. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. It is treated as inorganic compound. This is due to an obsolete concept known as vitalism, a belief that living things were fundamentally different from non-living things.