Q4.(a) Anhydrous calcium chloride is not used as a commercial de-icer because it reacts with water. The reaction with wa

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Q4 A Anhydrous Calcium Chloride Is Not Used As A Commercial De Icer Because It Reacts With Water The Reaction With Wa 1 (67.56 KiB) Viewed 10 times

Q4 A Anhydrous Calcium Chloride Is Not Used As A Commercial De Icer Because It Reacts With Water The Reaction With Wa 2 (72.02 KiB) Viewed 10 times

Q4.(a) Anhydrous calcium chloride is not used as a commercial de-icer because it reacts with water. The reaction with water is exothermic and causes handling problems. A student weighed out 1.00 g of anhydrous calcium chloride. Using a pipette, 25.0 cm³ of water were measured out and transferred to a plastic cup. The cup was placed in a beaker to provide insulation. A thermometer was mounted in the cup using a clamp and stand. The bulb of the thermometer was fully immersed in the water. The student recorded the temperature of the water in the cup every minute, stirring the water before reading the temperature. At the fourth minute the anhydrous calcium chloride was added, but the temperature was not recorded. The mixture was stirred, then the temperature was recorded at the fifth minute. The student continued stirring and recording the temperature at minute intervals for seven more minutes. The student's results are shown in the table below. Time/minutes Temperature/C Time/minutes Temperature/C 0 1 2 3 4 19.6 19.5 19.5 19.5 4 5 6 7 8 9 10 11 12 24.6 25.0 25.2 24.7 24.6 23.9 23.4 23.0 Plot a graph of temperature (-axis) against time on the grid below. Draw a line of best fit for the points before the fourth minute Draw a second line of best fit for the appropriate points after the fourth minute. Extrapolate both lines to the fourth minute.
(b) Use your graph to determine an accurate value for the temperature of the water at the fourth minute (before mixing). Temperature before mixing. (1) (c) Use your graph to determine an accurate value for the temperature of the reaction mixture at the fourth minute (after mixing). Temperature after mixing. (d) Use your answers from parts (b) and (c) to determine an accurate value for the temperature rise at the fourth minute. Give your answer to the appropriate precision. Temperature rise (e) Use your answer from part (d) to calculate the heat given out during this experiment. Assume that the water has a density of 1.00 g cm³ and a specific heat capacity of 4.18 JK-¹ g¹. Assume that all of the heat given out is used to heat the water. Show your working. (f) Calculate the amount, in moles, of CaCl in 1.00 g of anhydrous calcium chloride (M-111.0). Use your answers from parts (e) and (f) to calculate a value for the enthalpy change, in kJ mol, for the reaction that occurs when anhydrous calcium chloride dissolves in water. CaCl(s) 39 CaCl(aq) (1) ☎ (1) (1)