GCE Chemistry Q&A

Biodegradable polymers usually consist of bonds that can be hydrolysed, such as ester linkage or peptide bonds.

Polyalkene only contains a C-C bond in the main chain and the C-C bond cannot be hydrolysed.

The first step in distillation of crude oil is the oil must be heated until it is a gas. The first step in distillation of aid is the air must be cooled/compressed until it becomes a liquid.

From the nitride ion to the aluminium ion, the Ionic radius decreases. Because all of them are isoelectronic. They contain the same number of occupied electron shells and have a similar shielding effect. However, from nitrogen to aluminium, increasing atomic number to increase the effective nucleus charge. Therefore, the attraction between the nucleus to outer shell electrons increases causing a smaller radius.

Giant ionic lattice.

Sodium fluoride does not conduct electricity when solid.

Sodium fluoride does conduct when in aqueous solution or molten

Because the ions cannot move in a solid and the ions are free to move when the substance is in solution / molten

The fluoride ion has a single charge and a small ionic radius, this leading to a strong attraction between the nucleus and electron cloud. So the electron cloud is difficult to distort.

Strong electrostatic attraction between cations and delocalised electrons.

Aluminium produces 3 electrons per ion to form Al³⁺

When metal connects to a potential difference, the delocalised electrons flow. layers of ions slide over each other without breaking the metallic bond.

Thermal stability increases down Group 2, since the ionic radius increases and polarizing power of cations decreases while the charge remains the same. N−O breaks less easily.

In dry ether, since LiAlH₄ is very reactive and reacts with water.

During the reduction process, LiAlH₄ act as a nucleophile to attack the carbon atom in the C=O bond, which has a positive dipole.

However, in the alkene C=C bond is non-polar, with high electron density between the C=C bond, nucleophiles are repelled by π electrons of the C=C bond.

V⁵⁺ ion is very small and highly charged, i.e., it has high charge density, so it would polarise two water molecules, causing the O-H bond to break and lose hydrogen ions.

Phenol is more reactive than benzene since the lone pair of electrons on the oxygen is delocalised into the conjugated pi system of the benzene ring., which increases the electron density of the benzene ring, making it more available for electrophilic attack.

Mn²⁺ has five d electrons, making a half-filled 3d sublevel, so is more stable than Mn³⁺, the equilibrium favours the right-hand side(reduction side), making the potential more positive. Fe²⁺ has six d electrons so is less stable than Fe3+, and equilibrium favours the left-hand side (oxidation side), making the potential less positive.

Atoms with the same atomic number and different mass numbers.

A beam of high-energy electrons strikes the gaseous bromine molecule, knocking off an electron.

Equation :Br₂+ e^-->Br₂⁺+2e^-

It is the strong electrostatic attraction between the shared pair of electrons of the covalent bond and the nuclei of the silicon atom and the oxygen atom.

Similarities: both molecules contain a σ-bond, and orbitals show an end-on overlap pattern.

Difference: carbon dioxide contains a sideways overlap of orbitals, forming a π–bond with the oxygen atom.

There are two sets of bonding electrons and no lone pairs about the carbon atom, which are arranged to minimise repulsion, resulting in a linear shape, a bond angle of 180°

The carbon atom is slightly positive δ+ and the oxygen atom slightly negative δ−, because oxygen is more electronegative than carbon.

Isotopes have the same electronic configuration, which means they have the same chemical reactivity.

Mg has more delocalised electrons while its ion is smaller than Na⁺ but with higher charge. Overall the charge density of Mg²⁺ ion is higher than that of Na⁺， leading to greater attraction between the delocalised electrons and the Mg²⁺ ions.

Moving across the period there is an increase in the number of protons number, the electrons are in the same shell, so there is a greater attraction between the nucleus and electrons, and more energy is needed to remove the outermost electron.

• Electron configuration for oxygen: 1s22s22p4
• Electron configuration for nitrogen: 1s22s22p3
• When removing the outermost electron, the electron is being removed from a 2p orbital that is paired from oxygen, less energy is needed to remove a paired electron due to the repulsion between the electrons.
• The electron is being removed from a 2p orbital that is unpaired for nitrogen, more energy is needed to remove an unpaired electron.

• The successive ionization energy has a general increase because the electrons that are being removed are getting closer to the nucleus, the ion is becoming increasingly more positive as well, and greater energy is needed to remove the electrons.
• There is a big jump between 5th-6th ionisation energies as the 6th electron is removed from a new shell
• There is a jump between 3rd - 4th ionisation energies as the 4th electron is removed from a new subshell (2s)

The rate of reaction will be slower for 1-chlorobutane since C‒Cl has a higher bond enthalpy. Besides, 1-chlorobutane is a primary halogenoalkane while 2-bromo-2- methylpropane is a tertiary halogenoalkane.

It should be a black solid since the boiling point of group 7 elements increases down the group due to increasing molar mass and van der Waal forces.

• With cold water: Cl₂ + H₂O ⇌ HCl + HOCl
• With cold, dilute aqueous alkali: Cl₂ + 2NaOH → NaClO + NaCl + H₂O
• With hot, concentrated aqueous alkali: 3Cl₂ + 6NaOH → NaClO₃ + 5NaCl + 3H₂O
• all of these reactions are disproportionation reactions because chlorine is both oxidised and reduced chlorine oxidised to +1, +1 and +5 for reaction with water, cold dilute alkali and hot conc alkali correspondingly.

Oxides of nitrogen react with water vapour in the atmosphere, leading to the formation of acid rain.

Catalyst decreases the activation energy required, more particles have the energy required for the reaction to take place and increases the number of successful collisions per unit time.

The rate equation of a reaction is rate=k[BrO₃^- ][Br^- ] [H⁺ ]²

Because there are 4 particles in the rate equation in the equation, but the collisions with more than 2 particles are unlikely.

Acidic: reversible reaction, low yield

Alkaline: irreversible reaction, higher yield compared with the acidic condition, however, needs an extra protonation step to obtain the carboxylic acid.

∆Stotal=∆Ssystem+∆Ssurroundings

∆Stotal decreases because ∆Ssystem and ΔH do not change with temperature, therefore ∆Ssurroundings must decrease, this is because ∆Ssurroundings = -ΔH/T , so as T increases -ΔH/T becomes less positive because ΔH is exothermic.

• The mixture contains a large amount of both ammonium ions and ammonia
• Added H⁺ reacts with ammonia to form ammonium ions: NH₃+H⁺->NH₄⁺
• Ammonia reacts with water to produce OH^- ions:NH₃+H₂O->NH₄⁺+OH^-
• Ratio of ammonium ions to ammonia hardly changes.

The shape is linear, with 180° bond angle, as there are 2 pairs of bonding electrons and no lone pairs around central Ag⁺, which adopt a position to minimise repulsion between electron pairs / bonds

Silver ion has a full d-subshell， so there are no d-d transitions of electrons, and no light has been absorbed.

Beryllium has a higher charge density，Beryllium ion is more polarizing, so the beryllium-chlorine bond has a higher degree of covalency.

Some silicon atoms of mass 28 lose two electrons/have a charge of 2⁺

Sillicon has a giant covalent structure, which means all of its atoms are joined together by covalent bonds, these bonds are very strong and need lots of energy to break, therefore, it has a high melting point and is resistant to heat.

There are no free electrons within the silicon dioxide structure, so the charge cannot be carried, which makes it an insulator.

For the aluminium atom, the first electron is removed from the 3p orbital.

For the magnesium atom , the first electron is removed from the 3s orbital.

P electron is shielded by the s electrons so it requires less energy to be removed.

Delocalised electrons in the aluminium metallic bonding can move and carry charges

Aluminium has low density, also ductile so it can be drawn into wires.

The mixture is fractionally distilled and the distillate condensed at a suitable temperature is collected

Advantage: energy produced during the procedure can be used to generate electricity or heat locally.

Disadvantage: toxic gas may be produced.

Carbon monoxide may be produced due to insufficient oxygen supply, which is toxic and combines with haemoglobin, causing suffocation.

X‑ray diffraction showed that all C-C bonds are the same length in benzene, in Kekulé structure the C=C bonds would be shorter than the C-C bonds.

E‑hexa‑1,3‑diene is more stable than E‑hexa‑1,4‑diene since the two double bonds are close to each other, and some delocalization of pi-bonds occurs.

Transition metals have variable oxidation states, which means they can be easily oxidized and reduced back to their original oxidation state, donate and accept electrons from other species.

Monodentate: forms a sone dative bond.

Ligand: a species with a lone pair of electrons that can form a dative bond to a central transition metal ion.