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Chemistry

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Showing 726 to 750 of 1398 questions (page 30 of 56).

726. The reaction of a carboxylic acid with an alcohol in the presence of an acid catalyst is called

A. nitration B. esterification C. hydrolysis D. saponification E. decarboxylation

727. At its isoelectric point, an amino acid exists mainly as

A. a neutral unionized molecule B. a cation C. a zwitterion D. an anion E. a free radical

728. The linkage joining amino acid residues in a protein is

A. an ionic bond B. an ester linkage C. a glycosidic bond D. a peptide bond E. a disulphide bond only

729. Nylon 6,6 is an example of

A. a condensation polymer B. an addition polymer C. a natural polymer D. an elastomer formed by vulcanization E. a silicone

730. Which of the following is a reducing sugar?

A. sucrose B. starch C. glycogen D. cellulose E. glucose

731. The percentage of nitrogen in urea is about

A. 35% B. 60% C. 46% D. 82% E. 21%

732. Depletion of stratospheric ozone is mainly caused by

A. nitrogen gas B. chlorofluorocarbons C. methane D. sulphur dioxide E. carbon dioxide

733. Acid rain is caused mainly by the oxides of

A. carbon and hydrogen B. sulphur and nitrogen C. sodium and potassium D. silicon and boron E. iron and copper

734. The chief greenhouse gas responsible for the enhanced greenhouse effect is

A. nitrogen B. argon C. helium D. carbon dioxide E. oxygen

735. The stationary phase in thin layer chromatography is usually

A. silica gel or alumina B. the mobile solvent C. air D. water only E. the sample itself

736. The molar mass of carbon dioxide is

A. 48 g mol-1 B. 44 g mol-1 C. 12 g mol-1 D. 28 g mol-1 E. 32 g mol-1

737. One atomic mass unit is equal to

A. 1.661 x 10^-24 kg B. 9.1 x 10^-31 kg C. 6.02 x 10^-23 kg D. 1.661 x 10^-27 kg E. 1.6 x 10^-19 kg

738. The total number of atoms in one mole of methane is

A. 1.204 x 10^24 B. 3.01 x 10^24 C. 2.41 x 10^24 D. 6.02 x 10^23 E. 5 x 10^23

739. The molecular formula of a compound is related to its empirical formula by

A. multiplication by a whole number B. addition of a constant C. subtraction of hydrogen D. the ratio of densities only E. division by a whole number

740. Percentage yield is calculated as

A. actual yield minus theoretical yield B. moles of product times 100 C. actual yield divided by theoretical yield times 100 D. mass of reactants divided by mass of products E. theoretical yield divided by actual yield times 100

741. Distillation under reduced pressure is used for liquids that

A. are immiscible with water B. decompose at their normal boiling points C. form no vapour D. have very low boiling points E. are highly volatile

742. A desiccator is used to

A. distil liquids B. weigh precipitates C. dissolve solids D. keep substances free from moisture while cooling E. heat substances strongly

743. A sharp and constant melting point is used as a criterion of

A. purity B. density C. solubility D. conductivity E. volatility

744. In descending paper chromatography, the solvent moves

A. horizontally only B. in a circle C. in the vapour phase only D. upwards by capillary action E. downwards under gravity

745. At constant volume, the pressure of a fixed mass of gas is directly proportional to its

A. number of collisions only B. volume C. absolute temperature D. density E. molar mass

746. The volume occupied by 2 moles of an ideal gas at STP is

A. 44.8 dm3 B. 11.2 dm3 C. 22.4 dm3 D. 5.6 dm3 E. 24.0 dm3

747. Real gases deviate most from ideal behaviour at

A. high temperature and low pressure B. low temperature and high pressure C. standard conditions D. high temperature and high pressure E. low temperature and low pressure

748. For an ideal gas, the compressibility factor Z is

A. 1 B. equal to the pressure C. greater than 1 always D. less than 1 always

749. Plasma differs from an ordinary gas in that it consists largely of

A. molecules only B. liquid droplets C. ions and free electrons D. neutral atoms E. solid particles

750. Evaporation of a liquid causes cooling because

A. the liquid absorbs cold from the air B. the pressure increases C. the volume decreases D. the density increases E. the fastest molecules escape, lowering the average kinetic energy of those left

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