This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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Here are the solutions to the questions: 6. State two methods that can be used to remove water hardness. • Boiling • Adding washing soda (sodium carbonate) 7. (a) Define the term solubility. Solubility is the maximum mass of a solute that can dissolve in a given mass of solvent at a specific temperature to form a saturated solution. (b) Use the data to calculate the solubility of solid Q. Step 1: Calculate the mass of the saturated solution. Mass of saturated solution = Mass of (dish + saturated solution) - Mass of empty dish Mass of saturated solution = 62.5 g - 46.5 g = 16.0 g Step 2: Calculate the mass of dry solid Q (solute). Mass of dry solid Q = Mass of (dish + dry solid Q) - Mass of empty dish Mass of dry solid Q = 50.4 g - 46.5 g = 3.9 g Step 3: Calculate the mass of water (solvent). Mass of water = Mass of saturated solution - Mass of dry solid Q Mass of water = 16.0 g - 3.9 g = 12.1 g Step 4: Calculate the solubility of solid Q (mass of solute per 100 g of water). Solubility = Mass of solid QMass of water × 100 g Solubility = 3.9 g12.1 g × 100 g Solubility = 32.2314... g/100 g water The solubility of solid Q is 32.2 g/100 g water. 8. (a) What is meant by lattice energy? Lattice energy is the energy change when one mole of an ionic compound is formed from its gaseous ions under standard conditions. (b) Use the information below to calculate the heat of solution of calcium chloride. The heat of solution ( H_sol) can be calculated using Hess's Law: H_sol = Lattice energy (dissociation) + Hydration energy of cations + Hydration energy of anions The given lattice energy for CaCl_2 is -2195 kJ/mol, which is the energy released when the lattice is formed from gaseous ions. Therefore, the energy required to dissociate the lattice into gaseous ions is +2195 kJ/mol. For CaCl_2, there is one Ca^2+ ion and two Cl^- ions. Step 1: Write the equation for the heat of solution. H_sol = - H_lattice (formation) + H_hydration(Ca^2+) + 2 × H_hydration(Cl^-) Step 2: Substitute the given values. H_sol = -(-2195 kJ/mol) + (-189 kJ/mol) + (2 × -384 kJ/mol) H_sol = 2195 kJ/mol - 189 kJ/mol - 768 kJ/mol Step 3: Calculate the heat of solution. H_sol = 2195 - 189 - 768 H_sol = 1238 kJ/mol The heat of solution of calcium chloride is +1238 kJ/mol. 9. (a) State Boyle's law. Boyle's law states that for a fixed mass of gas at constant temperature, the pressure of the gas is inversely proportional to its volume. (b) A gas occupies 500 cm^3 at 37°C and 100,000 Pa. What will be its volume at 10°C and 101,325 Pa? Use the combined gas law: (P_1 V_1)/(T_1) = (P_2 V_2)/(T_2) Step 1: Convert temperatures to Kelvin. T_1 = 37^ + 273.15 = 310.15 K T_2 = 10^ + 273.15 = 283.15 K Step 2: List the given values. P_1 = 100,000 Pa V_1 = 500 cm^3 T_1 = 310.15 K P_2 = 101,325 Pa T_2 = 283.15 K V_2 = ? Step 3: Rearrange the combined gas law to solve for V_2. V_2 = (P_1 V_1 T_2)/(P_2 T_1) Step 4: Substitute the values and calculate V_2. V_2 = (100,000 Pa) × (500 cm^3) × (283.15 K)(101,325 Pa) × (310.15 K) V_2 = (14157500000)/(31499993.75) V_2 = 449.43 cm^3 The volume of the gas will be 449 cm^3 (to 3 significant figures). 10. Describe how a solid sample of copper (II) carbonate can be prepared starting with copper metal. 1. React the copper metal with concentrated nitric acid to form a soluble copper (II) nitrate solution. Cu (s) + 4HNO_3 (conc) → Cu(NO_3)_2 (aq) + 2NO_2 (g) + 2H_2O (l) 2. Add a solution of a soluble carbonate, such as sodium carbonate, to the copper (II) nitrate solution. This will cause copper (II) carbonate to precipitate as it is insoluble. Cu(NO_3)_2 (aq) + Na_2CO_3 (aq) → CuCO_3 (s) + 2NaNO_3 (aq) 3. Filter the precipitate (copper (II) carbonate) from the solution. 4. Wash the solid copper (II) carbonate with distilled water to remove any soluble impurities. 5. Dry the solid copper (II) carbonate, for example, by placing it in a desiccator or in a warm oven. That's 2 down. 3 left today — send the next one.