Chemistry

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Showing 226 to 250 of 1398 questions (page 10 of 56).

226. One atomic mass unit is equal to

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

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

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

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

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

229. Percentage yield is calculated as

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

230. Distillation under reduced pressure is used for liquids that

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

231. A desiccator is used to

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

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

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

233. In descending paper chromatography, the solvent moves

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

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

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

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

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

236. Real gases deviate most from ideal behaviour at

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

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

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

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

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

239. Evaporation of a liquid causes cooling because

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

240. London dispersion forces become stronger as

A. molar mass and polarizability increase B. molar mass decreases C. the molecule becomes more polar D. temperature increases E. the molecule becomes smaller

241. The property of crystals by which physical properties differ along different directions is called

A. isotropy B. anisotropy C. isomorphism D. polymorphism E. cleavage

242. Two substances with the same crystalline form and analogous chemical formulae are said to be

A. polymorphic B. isomorphic C. allotropic D. amorphous E. isotopic

243. The total number of orbitals in the shell with n = 2 is

A. 2 B. 3 C. 4 D. 8 E. 9

244. For l = 2, the number of permitted values of the magnetic quantum number is

A. 1 B. 3 C. 5 D. 7 E. 2

245. The Pauli exclusion principle states that no two electrons in an atom can have

A. the same energy B. the same spin C. identical values of all four quantum numbers D. the same orbital E. opposite spins

246. The neutron was discovered by

A. J J Thomson B. Rutherford C. Chadwick D. Millikan E. Bohr

247. The lines in the hydrogen emission spectrum arise when electrons

A. are ejected from the atom B. move from lower to higher energy levels C. fall from higher to lower energy levels D. collide with the nucleus E. are shared between atoms

248. The bond angle in water is about 104.5 degrees rather than 109.5 degrees because

A. oxygen is sp2 hybridized B. the two lone pairs repel the bonding pairs more strongly C. hydrogen atoms repel each other D. the molecule is linear E. of hydrogen bonding within the molecule

249. A sigma bond is stronger than a pi bond because

A. it involves sideways overlap B. it involves head on overlap giving greater electron density between the nuclei C. it uses unhybridized orbitals D. it is formed later E. it involves fewer electrons

250. The bond order in a nitrogen molecule is

A. 1 B. 2 C. 3 D. 1.5 E. 2.5

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