RI 2026 Planning Experiments 2 Tutorial (ans)

-1- Planning Experiments Tutorial 2 – Gravimetry, Gas Collection, Energetics and Kinetics Question 1 (cover during planning tutorial) Procedure [5] Key points to be included in the procedure: ✓ Apparatus used: - boiling tube - Bunsen burner - Analytical/weighing balance ✓ Duration of heating: - Gentle heating at first - Strong heating for 10 minutes ✓ Allow the boiling tube and its contents to cool before weighing ✓ Repeat heating-cooling- weighing process till constant mass ✓ Mass taken: - empty boiling tube - total mass of boiling tube and sample - total mass after each round of heat-cool-weigh process Step 1: Using an analytical/weighing balance, weigh an empty, dry and clean boiling tube and record the mass. Step 2: Transfer about 2.00 g of the mixture of Mg(OH) 2 and Ba(OH)2 provided into the boiling tube. Weigh the boiling tube and the sample and record the total mass. Step 3: Using a Bunsen burner, heat the boiling tube with its contents gently at first, and then strongly for 10 minutes. Ensure that the water droplets that condensed on the cooler parts of the boiling tube is driven off during heating. Step 4: Allow the boiling tube and its contents to cool. Then weigh the cooled boiling tube and its contents and record the total mass. Step 5: Repeat this heating -cooling-weighing process until constant mass is achieved. Measurements and tabulation of experimental data Mass of empty boiling tube / g A Mass of boiling tube and sample / g B Mass of boiling tube and contents after first heating / g after second heating / g after third heating / g C D D [1 for table] Mass of sample (mixture of Mg(OH)2 and Ba(OH)2) used = (B – A) g Mass of H2O lost = (B – D) g [1] Treatment of results Amount of H2O lost = (B – D)/18.0 mol Mg(OH)2(s) ⎯⎯→ MgO(s) + H2O(g) Amount of Mg(OH)2 decomposed = Total amount of H2O lost = (B – D)/18.0 mol Hence, mass of Mg(OH)2 in the mixture = (58.3)(B – D)/18.0 g [1] Percentage by mass of Mg(OH)2 in the mixture = [(58.3)(B – D)/18.0]  (B – A) x 100% [1]

-2- Question 2 (cover during planning tutorial) (a) Diagram of the set-up [2] ✓ Labeling of apparatus used ✓ Appropriate choice of apparatus to collect gas (e.g. 100 cm3 gas syringe). ✓ Reactants not mixed yet ✓ Air-tight and closed system by labeling the stopper to ensure no loss of gas Pre-calculations Mass of BaSO3 to be used Assume that 50.0 cm3 of SO2 gas is collected. As 1 mole of gas occupies a volume of 24 dm3 under laboratory conditions, Amount of SO2 = 50.0 24000 = 2.08 x 10−3 mol BaSO3(s) + 2HCl(aq) → BaCl2(aq) + SO2(g) + H2O(l) Amount of BaSO3 = 2.08 x 10–3 mol Molar mass of BaSO3 = 137.3 + 32.1 + 3(16.0) = 217.4 g mol–1 Mass of BaSO3 = (2.08 x 10–3)(217.4) = 0.4529 = 0.453 g [1] Volume of HCl(aq) to be used Amount of HCl(aq) = (2)(2.08 x 10–3) = 4.16 x 10–3 mol Volume of HCl to be used = (4.16 x 10–3) / 0.200 x 1000 = 20.8 cm3 [1] Since HCl(aq) has to be in excess so that the BaSO3 used is completely reacted, a suitable volume of HCl(aq) to be used is 25 cm3. [1] Procedure [5] 1. Using a burette, add 25.00 cm3 of HCl(aq) into a clean and dry 250 cm3 conical flask with a side arm. 2. Using an analytical balance, weigh accurately about 0.453 g of BaSO3 in a small tube and tie it to a string. 3. Set up the apparatus as shown above. 4. Lower the filled tube into the conical flask, taking care that the reagents do not mix. Stopper the conical flask. 5. Check that the initial reading of the 100 cm3 graduated gas syringe is set at the zero mark. 6. At a suitable time, loosen the stopper slightly to release the string to allow mixing of the reagents. Stopper the conical flask immediately. 7. Swirl the conical flask to ensure that the reagents are well mixed. 8. Allow the reaction to progress until it has ceased as indicated by a constant reading of the syringe. 9. Record the final reading on the graduated gas syringe. 10. Record temperature and pressure of the collected gas using a thermometer and a barometer respectively. 11. Repeat the experiment to get consistent results of volume of SO2 gas collected.

-3- Key Points: ✓ Appropriate apparatus used o Analytical balance to weigh BaSO3 o Burette/measuring cylinder to measure HCl(aq) ✓ Record initial and final reading of gas syringe ✓ Swirl and allow the reaction to complete (indicated by a constant reading of the syringe) ✓ Record temperature and pressure of the collected gas ✓ Repeat experiment to obtain consistent results Calculations to obtain molar gas constant, R Let the mass of solid BaSO3 used be m g Amount of BaSO3 used = Amount of SO2 formed = m 217.4 mol [1] Let the average pressure, volume and temperature of the SO 2 collected be P Pa, V cm3 and T K respectively. R = PV nT = P × V × 10-6 m 217.4 × T = P × V × 10-6 × 217.4 m × T J K-1 mol-1 [1] (b) Dilute sulfuric acid should not be used because the layer of insoluble BaSO4 forming around BaSO3(s) could stop the reaction prematurely. [1] (c) The reaction of acid and metal will product H2 gas. H2 deviates less from ideal gas behaviour since the intermolecular forces of attraction between H 2 molecules are weaker than that between SO2 molecules. [1] Question 3 (covered on IVY during T2W10) (a) Pre-calculations [2] Let volume of CuSO4 used be 25.0 cm3 n(CuSO4) used = 25.0 / 1000 x 1.00 = 0.0250 mol n(Zn) reacted = 0.0250 mol Mass of Zn reacted = 0.0250 x 65.4 = 1.635 g Since Zn is in excess, use 2.00 g of Zn. Note: • Set volume of CuSO4(aq) to be between 25 cm3 and 70 cm3. Volume of solution (assume capacity of Styrofoam cup is 200 cm 3) o should be sufficient to submerge the bulb of the thermometer o should not exceed more than half the capacity of the Styrofoam cup (up to 100 cm 3) o should allow for experiment to be repeated • Mass of Zn used must also allow for experiment to be repeated.

-4- Procedure [5] 1 Place the styrofoam cup in the 250 cm3 beaker. 2 Using a burette (or 25.0 cm3 pipette), add 25.0 cm3 of CuSO4 into the styrofoam cup and put the lid on. 3 Using an analytical balance, weigh accurately about 2. 00 g of Zn in a clean and dry weighing bottle. Record the total mass of Zn and weighing bottle. 4 Insert the thermometer through the lid and ensure that the bulb of the thermometer is in contact with the CuSO4. Record the temperature at time = 0 min. Start timing using the stopwatch. 5 Record the temperature of the CuSO4 every 0.5-minute interval until 2.5 minutes. 6 At exactly 3 minutes, open the lid of the cup and transfer the Zn carefully into the CuSO4. Replace the lid quickly. 7 Using the thermometer, stir the mixture gently. 8 Record the temperature of the mixture at every 0.5 -minute interval until there are 5 temperature readings after the highest temperature recorded. 9 Reweigh the weighing bottle with any residual Zn and record this mass reading. 10 Rinse out the styrofoam cup and the weighing bottle and dry them. Repeat steps 1 to 9 to obtain another set of data to plot another graph. Obtain a second value of Tmax and enthalpy change of reaction and find the average value for the enthalpy change of reaction. Key Points: ✓ use of appropriate apparatus (and its capacity) and instrument ✓ use of Styrofoam cup with lid ✓ appropriate mass of Zn to be used (Zn is in excess and allow for expt to be repeated) ✓ appropriate volume of CuSO4 to be used (between 25 cm3 and 70 cm3) ✓ mass measurements (i.e. weighing by difference to determine the mass of Zn used) ✓ starting stopwatch and recording at least 3 temperature readings before addition of Zn ✓ recording at least 5 temperature readings after the highest temperature is reache