(a)(i) What are acidic oxides?
(ii) Give one example of each of the following oxides: I. acidic oxide; II. basic oxide; III. amphoteric oxide; IV. neutral oxide
(b)(i) Define each of the following terms; I. Heat II. Heat of neutralization
(ii) Weite the above an equation to illustrate each of the terms in (b)(i) above
(ii) Given that the standard heat of combustion of butane (C\(_4\)H\(_{(10)}\) is + 5877 kJmol\(^{-1}\), calculate the heat of 14.5 g butane. [ H = 1, = 12 ]
(c) (i) Name two allotropes of sulphur
(ii) State one difference between the two allotropes.
(d)(i) Give two characteristics of noble eases
(ii) State one use each of I. He; II. Ar.
(e) State what is observed on warming ammonium trioxonitrate (V) with sodium hydroxide.
(a) Oxides
- (i) Acidic oxides are oxides (usually of non-metals) that react with water to form acids, and react with bases/alkalis to form a salt and water only.
- (ii) Examples: I. acidic oxide CO\(_2\) (or SO\(_2\), SO\(_3\)); II. basic oxide Na\(_2\)O (or CaO, MgO); III. amphoteric oxide Al\(_2\)O\(_3\) (or ZnO, PbO); IV. neutral oxide CO (or NO, H\(_2\)O, N\(_2\)O).
(b) Heat and heat of neutralization
- (i) I. Heat: a form of energy that flows from a body at a higher temperature to a body at a lower temperature. II. Heat of neutralization: the heat change when one mole of water is formed from the neutralization of an acid by a base (alkali) under standard conditions.
- (ii) Illustrative equations: heat change accompanying a reaction, e.g. \[C + O_2 \to CO_2,\ \Delta H = -393\ \text{kJ mol}^{-1}\] heat of neutralization, e.g. \[HCl_{(aq)} + NaOH_{(aq)} \to NaCl_{(aq)} + H_2O_{(l)},\ \Delta H = -57.3\ \text{kJ mol}^{-1}\]
- (iii) Heat released by 14.5 g of butane (C\(_4\)H\(_{10}\), molar mass \(= 48+10 = 58\ \text{g mol}^{-1}\); heat of combustion given as 5877 kJ per mole). Amount of butane \(= \dfrac{14.5}{58} = 0.25\ \text{mol}\). Heat evolved \(= 0.25 \times 5877 = 1469.25\ \text{kJ}\). So about 1469 kJ of heat is released (combustion is exothermic).
(c) Sulphur
- (i) Two allotropes: rhombic (alpha) sulphur and monoclinic (beta) sulphur.
- (ii) Difference: rhombic sulphur is the stable form below 96 degrees Celsius, while monoclinic sulphur is stable between 96 degrees Celsius and its melting point (about 119 degrees Celsius); they also differ in crystal shape (rhombic is octahedral, monoclinic is needle-shaped).
(d) Noble gases
- (i) Two characteristics: they are chemically inert/unreactive (stable, filled outer shells); they are monatomic, colourless gases with very low melting and boiling points.
- (ii) Uses: I. He used to fill balloons and airships, and (with oxygen) in breathing mixtures for divers. II. Ar used to provide an inert atmosphere in electric (filament) light bulbs and in welding.
(e) On warming ammonium trioxonitrate(V) (ammonium nitrate) with sodium hydroxide, a colourless gas with a pungent, choking smell (ammonia) is evolved which turns moist red litmus paper blue: \[NH_4NO_3 + NaOH \to NaNO_3 + H_2O + NH_3\uparrow\]
(a) Oxides
- (i) Acidic oxides are oxides (usually of non-metals) that react with water to form acids, and react with bases/alkalis to form a salt and water only.
- (ii) Examples: I. acidic oxide CO\(_2\) (or SO\(_2\), SO\(_3\)); II. basic oxide Na\(_2\)O (or CaO, MgO); III. amphoteric oxide Al\(_2\)O\(_3\) (or ZnO, PbO); IV. neutral oxide CO (or NO, H\(_2\)O, N\(_2\)O).
(b) Heat and heat of neutralization
- (i) I. Heat: a form of energy that flows from a body at a higher temperature to a body at a lower temperature. II. Heat of neutralization: the heat change when one mole of water is formed from the neutralization of an acid by a base (alkali) under standard conditions.
- (ii) Illustrative equations: heat change accompanying a reaction, e.g. \[C + O_2 \to CO_2,\ \Delta H = -393\ \text{kJ mol}^{-1}\] heat of neutralization, e.g. \[HCl_{(aq)} + NaOH_{(aq)} \to NaCl_{(aq)} + H_2O_{(l)},\ \Delta H = -57.3\ \text{kJ mol}^{-1}\]
- (iii) Heat released by 14.5 g of butane (C\(_4\)H\(_{10}\), molar mass \(= 48+10 = 58\ \text{g mol}^{-1}\); heat of combustion given as 5877 kJ per mole). Amount of butane \(= \dfrac{14.5}{58} = 0.25\ \text{mol}\). Heat evolved \(= 0.25 \times 5877 = 1469.25\ \text{kJ}\). So about 1469 kJ of heat is released (combustion is exothermic).
(c) Sulphur
- (i) Two allotropes: rhombic (alpha) sulphur and monoclinic (beta) sulphur.
- (ii) Difference: rhombic sulphur is the stable form below 96 degrees Celsius, while monoclinic sulphur is stable between 96 degrees Celsius and its melting point (about 119 degrees Celsius); they also differ in crystal shape (rhombic is octahedral, monoclinic is needle-shaped).
(d) Noble gases
- (i) Two characteristics: they are chemically inert/unreactive (stable, filled outer shells); they are monatomic, colourless gases with very low melting and boiling points.
- (ii) Uses: I. He used to fill balloons and airships, and (with oxygen) in breathing mixtures for divers. II. Ar used to provide an inert atmosphere in electric (filament) light bulbs and in welding.
(e) On warming ammonium trioxonitrate(V) (ammonium nitrate) with sodium hydroxide, a colourless gas with a pungent, choking smell (ammonia) is evolved which turns moist red litmus paper blue: \[NH_4NO_3 + NaOH \to NaNO_3 + H_2O + NH_3\uparrow\]
