Topic 1 & 2
A was found to contain 54.5% C and 9.1% H by mass, the remainder being oxygen. Determine the empirical formula of the compound.
C2H4O
State the electron arrangement of nitrogen and explain why it is found in period 2 and group 5 of the periodic table.
2,5
Electrons are in two energy levels and it has five valence electrons.
In aqueous solution, potassium hydroxide and hydrochloric acid react as follows.
KOH(aq) + HCl(aq) → KCl(aq)+ H2O(l)
The data below is from an experiment to determine the enthalpy change of this reaction.
50.0 cm3 of a 0.500 mol dm–3 solution of KOH was mixed rapidly in a glass beaker with 50.0 cm3 of a 0.500 mol dm–3 solution of HCl.
Initial temperature of each solution = 19.6°C
Final temperature of the mixture = 23.1°C
State, with a reason, whether the reaction is exothermic or endothermic.
Exothermic because the temperature rises and heat is released.
Ammonia is produced by the Haber process according to the following reaction.
N2(g) + 3H2(g) 2NH3(g) H is negative
State the equilibrium constant expression for the above reaction.
Kc=[NH3]2/[H2]3[N2]
Name the compound C2H4 and draw its structural formula
ethene
CH2=CH2
The relative atomic mass of chlorine is 35.45. Calculate the percentage abundance of the two isotopes of chlorine, 35-Cl and 37-Cl in a sample of chlorine gas.
35-Cl: 77.5%
37-Cl: 22.5%
Explain why the bonds in silicon tetrachloride, SiCl4, are polar, but the molecule is not.
The bonds are polar because Cl is more electronegative than Si.
The molecule is symmetrical so all of the polar effects cancel out.
When excess lumps of magnesium carbonate are added to dilute hydrochloric acid the following reaction takes place.
MgCO3(s) + 2HCl(aq) → MgCl2(aq) + CO2(g) + H2O(l)
State and explain three ways in which the rate of this reaction could be increased.
1. Use powdered MgCO3; increased surface area
2. Increase temperature; more of the collisions are successful
3. Increase Acid Concentration; more frequent collisions
4. Add Catalyst; lowers activation energy
The equilibrium reached when ethanoic acid is added to water can be represented by the following equation:
CH3COOH(l) + H2O(l) --> CH3COO–(aq)+H3O+(aq)
Define the terms Brønsted-Lowry acid and Lewis base, and identify two examples of each of these species in the equation.
Bronsted-Lowry Acid: proton donor (CH3COOH and H3O+)
Lewis Base: electron pair donor (H2O and CH3COO–)
Solid sodium chloride does not conduct electricity but molten sodium chloride does. State the products formed and give equations showing the reactions at each electrode.
Sodium formed at cathode (negative electrode)
Na++e- --> Na
Chlorine formed at anode (positive electrode)
2Cl---> Cl2 + 2e-
Determine the volume of 1.50 mol dm–3 hydrochloric acid that would react with exactly 1.25 g of calcium carbonate.
16.7 cm3
Predict and explain the order of the melting point for propanol, butane and propanone with reference to their intermolecular forces.
Butane<Propanone<Propanol
London Dispersion<Dipole-Dipole<Hydrogen Bonding
State and explain the trend in the bond enthalpies of the C–Cl, C–Br and C–I bonds.
C-Cl>C-Br>C-I
Halogen size pushes bonding electrons further away from the nucleus and the bonds become longer.
The equation for the main reaction in the Haber process is
N2(g) + 3H2(g) --> 2NH3(g) ∆H is negative
Use this information to state and explain the effect on the yield of ammonia of increasing
(i) pressure
(ii) temperature
(i) Yield increases and equilibrium moves to the right (more ammonia)
(ii) Yield decreases and equilibrium moves to the left (less ammonia)
Tin(II) ions can be oxidized to tin(IV) ions by acidified potassium permanganate(VII) solution according to the following unbalanced equation.
__ Sn2+ + __MnO4– + __ H+ -->__ Sn4+ + __Mn2+ + __ H2O
5 Sn2+ + 2MnO4– + 16 H+ -->5 Sn4+ + 2Mn2+ + 8 H2O
State the names of the other three processes in the order in which they occur in a mass spectrometer.
Ionization
Acceleration
Deflection
Determine the oxidation numbers of copper in the species
[Cu(NH3)4]2+ and [CuCl4]2–
+2
+2
Calculate the enthalpy change, H4 for the reaction
C + 2H2 + O2 --> CH3OH H4
using Hess’s Law, and the following information.
CH3OH + O2 --> CO2 + 2H2O H1 = -676 kJ mol-1
C + O2 --> CO2 H2 = -394 kJ mol-1
H2 + O2 --> H2O H3 = -242 kJ mol-1
H4= -202 kJ mol-1
The equation for the decomposition of hydrogen iodide is
2HI(g) H2(g) + I2(g) DHӨ = +52 kJ
Predict and explain the effect on the position of equilibrium of
(i) increasing the pressure, at a constant temperature.
(ii) increasing the temperature, at constant pressure.
(iii) adding a catalyst, at constant temperature and pressure.
(i) no effect: equal gas molecules on both sides
(ii) shift to the right: endothermic reaction
(iii) no effect: catalyst speeds up both forward and reverse reaction equally.
Both zinc and tin are used to coat iron to prevent it from rusting. Once the surface is scratched, oxygen and water containing dissolved ions come into contact with the iron and the coating metal.
State and explain whether zinc or tin would be more effective in preventing iron from rusting under these conditions.
Zinc is more readily oxidized than iron and so protects it by reacting preferrentially.
Explain how successive ionization energies account for the existence of three main energy levels in the sodium atom.
There are large increases in ionization energy when the 2nd and 10th electrons are removed. The 1st electron is further from the nucleus than the 2nd electron and the 9th electron is further from the nucleus than the 10th electron. The large increases indicate changes in main energy levels.
State the meaning of the term hybridization. State the type of hybridization shown by the nitrogen atoms in N2, N2H2, and N2H4.
Hybridization: Mixing/Merging of atomic orbitals
N2: sp
N2H2: sp2
N2H4: sp3
Oxygen and nitrogen monoxide react together to form nitrogen dioxide.
O2(g) + 2NO(g) → 2NO2(g)
When the initial values are [O2(g)] = 1.0×10–2 mol dm–3 and [NO(g)] = 3.0×10–2 mol dm–3, the initial rate of reaction is 6.3×10–4 mol dm–3s–1. Write the rate expression for this reaction and calculate the rate constant, stating its units.
rate = k[NO]2[O2]
k=70 mol-2dm6s-1
The hydrogen ion concentration in pure water varies with temperature. At a particular temperature [H+] =1.7×10–7 mol dm–3. State the expression for the ionic product constant of water, Kw, and calculate the value of Kw at this temperature.
Kw=[H+][OH]/[H3O+][OH-]
=2.89x10-14
There are geometrical isomers of the cyclic compound C4H6Cl2. Draw the structural formula of two isomers and explain why these two isomers exist.
cis-isomer
trans-isomer
There is restricted rotation because C-C bond is now part of a cyclic system.