(a) Distinguish between molecular formula and structural formula
(b) List three factors that determine the ionization energy of an atom.
(c) State the two conditions necessary for the establishment of a chemical equilibrium
(d) Consider the following table
| Element |
A |
B |
C |
| Ionization energy KJ mol\(^{-1}\) |
619 |
518 |
594 |
(d)(i) State which of the elements is the strongest reducing agent.
(ii) Give a reason for the answer stated in (d)(i)
(e) State Graham's law of diffusion
(f) Consider the following salts: \(\mathrm{Mg(NO_3)_2}\), \(\mathrm{CaCO_3}\), \(\mathrm{Na_2SO_4}\). State which of the salts is/are:
(i) readily soluble in water:
(ii) insoluble in water.
(g) Classily each of the following products as addition polymer or condensation polymer:
(i) protein:
(ii) perspex:
(iii) nylon.
(h) Define atomic radius.
(i) Explain briefly why ethanol has a higher boiling point than propane even though they both have comparable molar masses.
(j) State three significance of the pH value in everyday life.
(a) Molecular formula and structural formula
A molecular formula shows the actual number of atoms of each element present in one molecule of a compound (for example ethanol \( C_2H_6O \)). A structural formula shows how those atoms are arranged and joined together by bonds (for example \( CH_3CH_2OH \)).
(b) Three factors that determine ionization energy
- The atomic radius (distance of the outermost electron from the nucleus).
- The nuclear charge (number of protons).
- The shielding (screening) effect of the inner electrons.
(c) Two conditions for chemical equilibrium
- The reaction must be reversible.
- The system must be closed (no reactant or product enters or leaves) and kept at constant temperature.
(d) Ionization energies: A = 619, B = 518, C = 594 \( \text{kJ mol}^{-1} \).
| Element | A | B | C |
|---|
| Ionization energy / kJ mol\(^{-1}\) | 619 | 518 | 594 |
(i) The strongest reducing agent is B.
(ii) B has the lowest ionization energy, so it loses (donates) its outermost electron most easily; a good reducing agent is one that readily gives up electrons.
(e) Graham's law of diffusion
At constant temperature and pressure, the rate of diffusion of a gas is inversely proportional to the square root of its density (or relative molecular mass): \( \text{rate} \propto \dfrac{1}{\sqrt{M}} \).
(f) (i) Readily soluble in water: \( Mg(NO_3)_2 \) and \( Na_2SO_4 \) (all nitrates and all sodium salts are soluble). (ii) Insoluble in water: \( CaCO_3 \).
(g) (i) Protein: condensation polymer. (ii) Perspex: addition polymer. (iii) Nylon: condensation polymer.
(h) Atomic radius
Atomic radius is half the distance between the nuclei of two identical atoms joined by a single covalent bond (half the internuclear distance).
(i) Ethanol versus propane
Ethanol molecules contain an \( -OH \) group and form hydrogen bonds between neighbouring molecules. These hydrogen bonds are much stronger than the weak van der Waals (dispersion) forces between propane molecules, so more energy is needed to separate ethanol molecules, giving it the higher boiling point even though the molar masses are comparable.
(j) Three significances of pH in everyday life
- Control of soil pH so that crops grow well (agriculture).
- Maintaining the correct pH of blood and other body fluids for good health (medicine).
- Quality control in the manufacture of foods, drinks, drugs and cosmetics, and in the treatment of drinking water.
(a) Molecular formula and structural formula
A molecular formula shows the actual number of atoms of each element present in one molecule of a compound (for example ethanol \( C_2H_6O \)). A structural formula shows how those atoms are arranged and joined together by bonds (for example \( CH_3CH_2OH \)).
(b) Three factors that determine ionization energy
- The atomic radius (distance of the outermost electron from the nucleus).
- The nuclear charge (number of protons).
- The shielding (screening) effect of the inner electrons.
(c) Two conditions for chemical equilibrium
- The reaction must be reversible.
- The system must be closed (no reactant or product enters or leaves) and kept at constant temperature.
(d) Ionization energies: A = 619, B = 518, C = 594 \( \text{kJ mol}^{-1} \).
| Element | A | B | C |
|---|
| Ionization energy / kJ mol\(^{-1}\) | 619 | 518 | 594 |
(i) The strongest reducing agent is B.
(ii) B has the lowest ionization energy, so it loses (donates) its outermost electron most easily; a good reducing agent is one that readily gives up electrons.
(e) Graham's law of diffusion
At constant temperature and pressure, the rate of diffusion of a gas is inversely proportional to the square root of its density (or relative molecular mass): \( \text{rate} \propto \dfrac{1}{\sqrt{M}} \).
(f) (i) Readily soluble in water: \( Mg(NO_3)_2 \) and \( Na_2SO_4 \) (all nitrates and all sodium salts are soluble). (ii) Insoluble in water: \( CaCO_3 \).
(g) (i) Protein: condensation polymer. (ii) Perspex: addition polymer. (iii) Nylon: condensation polymer.
(h) Atomic radius
Atomic radius is half the distance between the nuclei of two identical atoms joined by a single covalent bond (half the internuclear distance).
(i) Ethanol versus propane
Ethanol molecules contain an \( -OH \) group and form hydrogen bonds between neighbouring molecules. These hydrogen bonds are much stronger than the weak van der Waals (dispersion) forces between propane molecules, so more energy is needed to separate ethanol molecules, giving it the higher boiling point even though the molar masses are comparable.
(j) Three significances of pH in everyday life
- Control of soil pH so that crops grow well (agriculture).
- Maintaining the correct pH of blood and other body fluids for good health (medicine).
- Quality control in the manufacture of foods, drinks, drugs and cosmetics, and in the treatment of drinking water.
