Chemistry Quiz: May/June 2009

What is the value of x in the empirical formula PbC8Hx?

• 16

• 6

• 20

• 5

What is the concentration of NaClO in the bleach when 25.0 cm3 of bleach is treated with an excess of aqueous H2O2, and 0.0350 mol of oxygen gas is given off?

• 0.875 mol dm–3

• 0.700 mol dm–3

• 1.40 mol dm–3

• 8.75 × 10–4 mol dm–3

What is the outer electronic configuration of the element with the first seven ionisation energies as follows: 1310, 3390, 5320, 7450, 11 000, 13 300, 71 000 kJ mol–1?

• 2s2

• 2s22p1

• 2s22p6

• 2s22p4

Which graph represents the number of unpaired p orbital electrons for atoms with proton numbers 13 to 18?

• number of unpaired electrons

• proton number

• CD

• AB

Which statement explains why the boiling point of methane is higher than that of neon?

• A molecule of methane has a greater mass than a molecule of neon.

• The molecule of methane is polar, but that of neon is not.

• Molecules of methane form hydrogen bonds, but those of neon do not.

• Molecules of methane have stronger intermolecular forces than those of neon.

In which reaction does the carbon-containing product have a smaller bond angle than the organic reactant?

• polymerisation of ethene

• methane and an excess of chlorine under ultraviolet light

• complete combustion of methane in air

• bromoethane refluxed with ethanolic sodium hydroxide

A crystal of iodine produces a purple vapour when gently heated. Which pair of statements correctly describes this process?

• covalent I

• permanent dipole-dipole I2

• covalent I2

• induced dipole-dipole I2

Hydrogen peroxide slowly decomposes into water and oxygen. The enthalpy change of reaction can be calculated using standard enthalpies of formation. Using a Hess cycle, what is the enthalpy change of reaction for this decomposition?

• –947.2 kJ mol–1

• –196 kJ mol–1

• –98 kJ mol–1

• +98 kJ mol–1

When copper is extracted from its ores, the metal is not pure enough for electrical uses. Why is silver found in the sludge formed during the purification process?

• Silver is less electropositive than copper.

• Silver reacts with the electrolyte to form an insoluble sulfate salt.

• Silver is more dense than copper and falls off the cathode.

• Silver reacts with the electrolyte to form an insoluble chloride salt.

The diagram shows the Maxwell-Boltzmann energy distribution curve for molecules of a mixture of two gases at a given temperature. For a reaction to occur the molecules must collide together with sufficient energy. Which pair of statements is correct when a catalyst is used?

• Ea1 catalysed reaction more effective collisions, Ea2 uncatalysed reaction fewer effective collisions

• Ea1 uncatalysed reaction fewer effective collisions, Ea2 catalysed reaction more effective collisions

• Ea1 catalysed reaction fewer effective collisions, Ea2 uncatalysed reaction more effective collisions

• Ea1 uncatalysed reaction more effective collisions, Ea2 catalysed reaction fewer effective collisions