RI 9729/04 2022 Planning

-1- Question 4 Planning: Measuring the activation energy for a reaction (a) amount of phenol = 0.01 x 75 1000 = 0.00075 mol mass of phenol = 0.00075 x (6 x 12.0 + 6 x 1.0 + 16.0) = 0.0705 g Procedure: 1. Using an analytical balance, weigh accurately about 0.0705 g of solid phenol in a clean and dry weighing bottle. Record the total mass of weighing bottle and solid. 2. Transfer all the phenol quantitatively to a 100 cm 3 beaker and dissolve it in some deionised water. Rinse the weighing bottle with small volumes of deionised water several times, adding each rinsing to the beaker. 3. Transfer the solution in the beaker quantitatively to a 75 cm3 graduated flask. Rinse the beaker with small volum es of deionised water several times, adding each rinsing to the graduated flask. 4. Fill the graduated flask to the 75 cm3 mark with more deionised water. Use the dropping pipette (or teat pipette or dropper) to add the deionised water drop-wise when nearing the mark. 5. Stopper the graduated flask and shake the solution thoroughly to ensure that it is homogeneous. Safety issue: Phenol is corrosive and toxic by skin absorption. Precaution: Wear gloves and goggles when performing the experiment. (b) Procedure 1. Using separate 25 cm3 measuring cylinders, add 15.0 cm3 of 0.10 mol dm–3 KBr solution, 15.0 cm3 of 0.2 mol dm–3 H2SO4 solution and 15 cm3 of 0.01 mol dm–3 phenol solution (prepared from 4(a)) to a 250 cm3 conical flask labelled reaction mixture. To this reaction mixture in the conical flask, add two drops of methyl red indicator. 2. Also, measure 15.0 cm 3 of 0.20 mol dm –3 KBrO3 solution using another 25 cm 3 measuring cylinder. 3. Place this conical flask containing the reaction mixture and measuring cylinder containing KBrO3 into a thermostatically controlled water bath set at 50 oC, with the reaction mixture immersed in the water bath. 4. Place a thermometer into the same conical flask. 5. When the temperature of the reaction mixture and KBrO3 solution reaches 50 oC, add 15.0 cm3 of 0.20 mol dm–3 KBrO3 solution into the conical flask containing the reaction mixture placed in the water bath. Start the stopwatch and swirl the mixture thoroughly to mix its contents while keeping the mixture still immersed in the water bath. 6. Stop the stopwatch when the solution turns from red to colourless and r ecord the time taken, t, for the solution to turn from red to colourless. 7. Repeat steps 1 to 6 four more times, each time with the temperature of the water bath in step 3 set at a different value of 10 oC, 20 oC, 30 oC and 40 oC. Key Points:  appropriate apparatus and capacity

-2-  appropriate volumes of KBr, KBrO3, H2SO4, phenol and methyl red indicator  starting stopwatch when KBrO 3 is added; stop stopwatch at end- point colour change and recording of time  Incubating reaction mixture in a water bath with a thermometer  Repeat procedure at different temperatures (at l