Cambridge O Level Chemistry 5070 Syllabus

How is an ion formed, and how do metals and non-metals form ions?

An ion forms when an atom loses or gains electrons. Metals lose electrons to form positive ions (cations); non-metals gain electrons to form negative ions (anions).

Define ionic bonding.

Ionic bonding is the strong electrostatic attraction between oppositely charged ions, formed by the transfer of electrons from a metal to a non-metal.

Define covalent bonding.

Covalent bonding is the sharing of one or more pairs of electrons between two non-metal atoms, so each atom achieves a stable (noble gas) electron configuration.

Describe metallic bonding.

Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and a 'sea' of delocalised (mobile) electrons.

Why do ionic compounds have high melting and boiling points?

They have a giant ionic lattice held together by strong electrostatic forces between oppositely charged ions, which require a lot of energy to overcome.

Why can ionic compounds conduct electricity when molten or in solution but not when solid?

When molten or dissolved, the ions are free to move and carry charge; when solid, the ions are held in fixed positions and cannot move.

Compare the structures and properties of diamond and graphite.

Diamond: each carbon bonded to 4 others in a giant rigid tetrahedral lattice, very hard, does not conduct electricity. Graphite: each carbon bonded to 3 others in layers with delocalised electrons, soft/slippery (layers slide), conducts electricity.

Why do simple molecular substances have low melting and boiling points?

They have weak intermolecular forces between molecules which require little energy to overcome, even though the covalent bonds within molecules are strong.

Why are metals good conductors of electricity and malleable?

Delocalised electrons are free to move and carry charge (conduction); layers of metal ions can slide over each other when a force is applied without breaking the metallic bonding (malleable).

Define the relative atomic mass (Ar) of an element.

The relative atomic mass is the average mass of the atoms of an element compared to 1/12 of the mass of a carbon-12 atom, taking into account the abundance of its isotopes.

What is the difference between an empirical formula and a molecular formula?

Empirical formula shows the simplest whole-number ratio of atoms of each element in a compound; molecular formula shows the actual number of atoms of each element in a molecule.

What is the formula and charge of the following ions: sulfate, nitrate, carbonate, hydroxide, ammonium?

Sulfate SO4^2-, nitrate NO3^-, carbonate CO3^2-, hydroxide OH^-, ammonium NH4^+.

What does a balanced chemical equation tell you and what must be equal on both sides?

It shows the reactants and products with state symbols and the ratio in which they react/form; the number of atoms of each element (and total charge) must be equal on both sides.

What do the state symbols (s), (l), (g) and (aq) represent?

(s) solid, (l) liquid, (g) gas, (aq) aqueous (dissolved in water).

What is the Avogadro constant and what is one mole?

The Avogadro constant is 6.02 x 10^23 per mole. One mole is the amount of substance containing the same number of particles as the Avogadro constant.

State the formula linking number of moles, mass and molar mass.

Number of moles = mass (g) / molar mass (g/mol).

What is the molar volume of any gas at room temperature and pressure (r.t.p.) and the formula linking moles and gas volume?

At r.t.p. one mole of any gas occupies 24 dm3 (24,000 cm3). Number of moles = volume of gas (dm3) / 24.

State the formula linking number of particles, moles and the Avogadro constant.

Number of particles = number of moles x Avogadro constant (6.02 x 10^23).

Define the concentration of a solution and give the two common units.

Concentration is the amount of solute dissolved in a given volume of solution; measured in g/dm3 or mol/dm3.

State the formula linking concentration, moles and volume of solution.

Concentration (mol/dm3) = number of moles of solute / volume of solution (dm3).

Define percentage yield and give its formula.

Percentage yield = (actual yield / theoretical yield) x 100. It compares the mass of product obtained to the maximum possible mass predicted from the equation.

Define electrolysis.

Electrolysis is the breaking down (decomposition) of an ionic compound, when molten or in aqueous solution, by the passage of an electric current.

Define electrolyte, anode and cathode.

Electrolyte: a molten or aqueous ionic compound that conducts electricity and is decomposed by it. Anode: the positive electrode. Cathode: the negative electrode.

At which electrode do cations and anions discharge, and what process occurs at each?

Cations (positive ions) move to the cathode where reduction (gain of electrons) occurs; anions (negative ions) move to the anode where oxidation (loss of electrons) occurs.

What are the products of electrolysis of molten lead(II) bromide?

Lead metal forms at the cathode and bromine gas (vapour) forms at the anode.

In the electrolysis of concentrated aqueous sodium chloride (brine), what is formed at each electrode?

Hydrogen gas at the cathode, chlorine gas at the anode, and sodium hydroxide solution remains in the electrolyte.

In aqueous electrolysis, what general rule decides whether hydrogen or a metal is discharged at the cathode?

If the metal is more reactive than hydrogen, hydrogen is discharged; if the metal is less reactive than hydrogen (e.g. copper), the metal is discharged.

Describe how electroplating an object with silver is carried out.

The object to be plated is the cathode, a piece of pure silver is the anode, and the electrolyte is a silver salt solution; silver ions are deposited onto the object at the cathode while the silver anode dissolves.

Describe how copper is purified (refined) by electrolysis.

The impure copper is the anode and a thin pure copper sheet is the cathode in copper(II) sulfate solution; copper dissolves from the anode and pure copper deposits on the cathode, leaving impurities as anode sludge.

Define exothermic and endothermic reactions in terms of heat and surroundings.

Exothermic reactions release/give out heat energy to the surroundings (temperature rises). Endothermic reactions absorb/take in heat energy from the surroundings (temperature falls).

Explain the energy change of an exothermic reaction in terms of bond breaking and bond making, and the sign of its enthalpy change.

Energy is taken in to break bonds and given out when bonds form; in an exothermic reaction more energy is released forming bonds than absorbed breaking them, so the overall enthalpy change is negative.