The relative atomic mass is the weighted average mass of all the isotopes occurring naturally in one mole of atoms of the element compared to the mass of 1/12 mol of carbon-12 so has no units.

The balanced equation is 4NH₃(g)  +  ­5O₂(g)     →      4NO(g)  +  6H₂O(l)

Amount of HCl in 150 cm³ of 0.20 mol dm⁻³ HCl(aq) = 150/1000 x 0.20 mol
Amount of HCl in 250 cm³ of 0.30 mol dm⁻³ HCl(aq) = 250/1000 x 0.30 mol
Amount of HCl in 400 cm³ of mixture = (150/1000 x 0.20) + (250/1000 x 0.30) mol
Amount of HCl in 1000 cm³ (1 dm³) of mixture = [(150/1000 x 0.20) + (250/1000 x 0.30)] x 1000/400 = 0.26 mol

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) so 1.60 g (0.1 mol) of methane requires 0.2 mol of oxygen (6.40 g) to combust completely. This means there will be 6.40 g (0.2 mol) of excess oxygen remaining and 0.1 mol of carbon dioxide product present (water is a liquid at STP) which will occupy 3 x 2.27 = 6.81 dm³.

The atomic number of Fe is 26 so it will contain 26 protons. Its mass number is 56 so there will be 30 neutrons in the isotope. Fe contains 26 electrons.  Three electrons have been removed to form Fe³⁺ so there will be 23 electrons remaining.

Emission spectra involve excited electrons falling from higher to lower energy levels. Electrons falling to the n = 1 level will have the highest energy as all these transitions occur in the ultraviolet region of the electromagnetic spectrum (when electrons fall to the n = 2 level the transitions occur in the visible region).

The element has 5 electrons in its incomplete 3p sub-level so is a p block element and will be in group 17. (You can also arrive at the answer by seeing that it has 17 electrons in total so the atomic number must be 17. This means the element is chlorine which is in group 17.)

The oxides of period 3 (Na → Cl) change from basic to acidic moving from left to right across the period with aluminium oxide having both basic and acidic properties.

All four compounds are ionic but the nitrate, sulfate and ammonium ions, (NO₃⁻, SO₄²⁻ and NH₄⁺) are complex ions which also contain covalent bonding. Potassium nitride, K₃N only contains K⁺ and N³⁻ ions.

CCl₄, NH₃ and H₂O all have four electron domains around the central atom. CCl₄ has four bonding pairs of electrons so has a regular tetrahedral shape with bond angles of 109.5^o. NH₃ has one non-bonding pair of electrons and H₂O has two non-bonding pairs of electrons. These non-bonding pairs exert a greater repulsion than bonding pairs so the bond angles are less than 109.5^o. BF₃ has three electron domains consisting of three bonding pairs of electrons so its shape is trigonal planar with bond angles of 120^o.

There is no hydrogen bonding between ethanal, CH₃CHO molecules so ethanal has the lowest boiling point (20.2 ^oC). Both ethanol and ethanoic acid have a hydrogen atom bonded directly to an electronegative oxygen atom so exhibit hydrogen bonding. The hydrogen bonding will be stronger in the carboxylic acid as the oxygen atom of the carbonyl group also draws electrons away from carbon atom bonded to the -OH group so that the polarity of the O-H bond increases. (Ethanol boils at 78.4 ^o.C and the boiling point of ethanoic acid is 118.1 ^oC.)

The three factors which increase the strength of metallic bonding are a decrease in the radius of the metal ion, an increase in the charge on the metal ion (these two factors increase the charge density) and the number of delocalized electrons. An increase in the number of electrons is not the same as an increase in the number of delocalized electrons. Potassium, for example, has 39 electrons whereas lithium only has 3 electrons but both have only one electron in the outer s orbital that can delocalize and the much smaller lithium ion means lithium has a much higher boiling point than potassium. 

The O−O bond in hydrogen peroxide, H₂O₂ is a single bond so is the weakest. The O=O bond in oxygen gas is the strongest as it is a double bond and the oxygen to oxygen bond in ozone is in-between as it is a resonance hybrid equivalent to a 1.5 bond.

Average bond enthalpies refer only to the gaseous state and additional enthalpy terms involving change of state are required for all the reactions except for the reaction between methane and chlorine where all the reactants and products are in the gaseous state.

Rate of reaction is measured as the change in concentration over time so will have the units of concentration time⁻¹.

E_a for the forward catalysed reaction is the difference between the starting energy and the peak of the dotted red line (catalysed pathway), ΔH is the difference in energy between the initial and final states and E_a for the reverse catalysed reaction is the difference between the new starting energy and the peak of the catalysed pathway.

If the first equation is written as ½H₂(g)  +  ½I₂(g)  ⇌  HI(g) then the equilibrium constant will be √K_c. The equilibrium constant for the reverse reaction will be (√K_c)⁻¹, i.e. 1 ÷ √(1.60 x 10²).

Brønsted-Lowry acids donate a proton to form their conjugate base, so NH₂⁻ is the conjugate base of NH₃ whereas ammonia itself is the conjugate base of NH₄⁺.

Sulfuric acid is a strong diprotic acid so [H⁺(aq)] will be equal to 2 x 10⁻² mol dm⁻³. pH = − log₁₀[H⁺(aq)] so the pH will be less than 2 but more than 1 (as [H⁺(aq) would need to be 10 x 10⁻² mol dm⁻³ for it to be 1). This has assumed that H₂SO₄ is a strong dibasic acid. In fact the first dissociation to HSO₄⁻ is strong but the second dissociation is not completely strong. Even so, the actual concentration of H⁺(aq) will still be more than 1 x 10⁻² (but less than 2 x 10⁻² mol dm⁻³) so the pH will between 1 and 2.

All four oxides listed are acidic but carbon dioxide only forms a weak acid in water. As rain water falls through the atmosphere it naturally dissolves carbon dioxide to become acidic but the lowest pH this can reach is about 5.6 so acid precipitation is defined as having a pH lower than 5.6.

The oxidation state of sulfur in sulfuric acid, H₂SO₄ is +6. In sodium thiosulfate, Na₂S₂O₃ and in sulfur dioxide, SO₂ it is +4 and in hydrogen sulfide, H₂S it is −2.

Oxidation always occurs at the anode. In a voltaic cell the anode is the negative electrode and in a electrolytic cell the anode is the positive electrode. For a voltaic cell to produce electrical energy the spontaneous chemical process must be exothermic, not endothermic

The molecule has the formula R-CO-R' so it is a ketone. The two functional groups in addition to the carbonyl group are a phenyl group and an alkyl goup.

The compound is an isomer of hexanol, C₆H₁₃OH, but the longest chain contains four carbon atoms and there is a hydroxyl group on the second carbon atom. It is also bonded to two methyl groups, one on the second carbon atom and one on the third, so it is 2,3-dimethylbutan-2-ol.

The reaction is an example of nucleophilic substitution. A nucleophile is an electron-rich species containing a non-bonding pair of electrons that it donates to an electron-deficient carbon. The carbon atom in the C−Br bond is electron deficient as bromine is more electronegative than carbon.

The equation for this esterification reaction is HCOOH + CH₃OH ⇌ HCOOCH₃ + H₂O

The ideal gas equation is pV = nRT. Since M_r of O₂ is 32, n = 1/32 mol. P = 1.0 x 10⁵ Pa = 1.0 x 10⁵ Nm⁻² and I J = 1 Nm

32 (mol⁻¹) x 1.0 x 10⁵ (Nm⁻²) x V (m³) = R (J K⁻¹ mol⁻¹) x T (K)

a plot of (3.2 x 10⁶)V against T will give a gradient of R in J K−1 mol−1)

When calculating IHD O atoms count as zero and Cl atoms can be considered to behave as H atoms so the formula can be reduced to C₁₂H₈. If it was fully saturated it would be C₁₂H₂₆ so it is 18 H atoms (or 9 H₂) short which means that the IHD Is 9. This can also be seen from the structural formula as the two benzene rings each have an IHD of 4 (three for the 'double bonds' and one for the ring) and the additional ring makes a total of 9.

The hydrogen atoms are in four different chemical environments. Although not asked for the ratio of the areas under each signal will be 6:3:2:1. The 6 is due to the six H atoms in the two -CH₃ groups bonded to the second carbon atom in the chain, the 3 is due to the three H atoms bonded to the fourth carbon atom in the chain, the 2 is due to the two hydrogen atoms bonded to the third carbon atom in the chain and the 1 is due to the single H atom bonded to the second carbon atom in the chain.