(a) (i) Define saturated solution.
(ii) Tha solubility of KNO\(_3\) at 20°C was 3.00 mol dm\(^{-3}\) If 67.0g of KNO\(_3\) was added to 250 cm\(^{-3}\) of water and stirred at 20°C, determine whether the solution formed was saturated or not at that temperature. [ KNO\(_3\) = 101.0 ]
(b) (i) Distinguish between dative bond and covalent bond.
(ii) Explain why sugar and common salt do not conduct electricity in the solid state.
(iii) State the type of intermolecular forces present in: I. hydrogen fluoride; II argon.
(iv) Consider the compounds with the following structures. S – H —- N and O – H —- N In which of the compounds is the hydrogen bend stronger? Give reason for your answer.
(c) (i) State Dalton’s Law of Partial Pressure.
(ii) If 200cm of carbon (IV) oxide were collected over water at 18°C and 700 mmHg, determine the volume of the dry gas at s.t.p. [ standard vapour pressure of water at 18°C = 15 mmHg]
Explanation
(a)(i) A saturated solution is that which contains the maximum amount of solute it can dissolve at a given temperature (in the presence of undissolved solute).
(ii) solubility of KNO\(_3\) in gdm\(^{-3}\) = 3.00 x 101. = 303
1000cm\(^{3}\) of saturated solution ---- 303g
250cm\(^{3}\) of the solution = \(\frac{303 \times 250}{1000}\) = 75.8 g.
Since the quantity of KNO\(_3\) added (67.0) to 250 cm\(^{3}\) of water is less than maximum amount required to form a saturated solution, then the solution is unsaturated.
(b)(i) In dative bond, only one of the participating atoms/species donates the electrons to be shared by both atoms while in covalent bond both participating atoms/species contribute equally the electrons being shared.
(ii) Sugar is covalent while common salt (NaCI) is electrovalent/ionic. Electrical conductivity (in compounds) depends on presence of mobile ions. Sugar does not conduct electricity because it does not contain ions (they are molecules) while solid common salt does not conduct electricity because its ions are not mobile.
(iii) I. Hydrogen bond.
(iv) H. Van der Waals forces.
(iv) O - H --- N Because oxygen is more electronegative and smaller in size than sulphur.
(c)(i) The total pressure exerted by a mixture of gases which do not-react chemically is equal to the sum of the individual partial pressures of the gases in the mixture.
(ii) pressure of the dry gas (P\(_1\) = 700 - 15 = 685 mmHg, V\(_1\) = 200 cm\(^3\), T\(_1\) = 18°C = 273 + 18 = 291K, P\(_2\) = 760 mmHg, T\(_2\) = 273
\(\frac{P_1V_1}{T_1}\) =\(\frac{P_2V_2}{T_2}\)
V\(_2\) = \(\frac{P_1V_1T_2}{P_2T_1}\)
\(\frac{685 \times 200 \times 273}{760 \times 291}\)
= 169.1 cm\(^{3}\)