Hydrochloric Acid and Calcium Carbonate It is required to follow-up the progress of the reaction between solid calcium carbonate CaCO3 and hydrochloric acid solution (H3O+ + Cl-). The equation of this reaction is: CaCO3(s) + 2 H3O+(aq) → Ca2+(aq) + CO2(g) + 3H2O(l) Experiment 1: At T = 25 ºC, a volume V=250mL of hydrochloric acid solution of concentration CA = 2mol.L-1 is introduced into a flask containing a piece of calcium carbonate of mass m = 20 g. by a convenient method, we measure the volume of carbon dioxide gas released at different times t. Document-1 shows the number of moles of the gas CO2 released at different instants of the reaction: t (s) n (CO2) (10 – 2 mol) 10 3.0 20 5 30 40 7 8.75 Document-1 60 11.25 80 13.25 100 14.75 120 15.5 Given: - Molar mass of calcium carbonate: M = 100 g.mol-1. Molar volume of gas: Vm = 24 L.mol-1. 1- Preliminary study 1.1- Identify the limiting reactant in the mixture. 1.2- Deduce, the nature (heterogeneous, homogeneous) of the mixture at the end of the gas release. 1.3- Specify whether the reaction ends at t =120s. 2- Kinetic Study 2.1- Plot the curve that represents the change in the number of moles of the gas released as a function of time: n(CO2) = f(t) in the interval of time: [0 -120 s]. Take the following scale: 1 cm for 10 s in abscissa and 1 cm for 2×10-2 mol in ordinate. 2.2- Determine the half-life time of this reaction. 2.3- At the instant t= 15s, the rate of formation of CO2 is r =2×10-3 mol.s-1. The rate of formation of CO2 at t =75s is r'. Choose by justifying the correct answer. a) r' < r b) r' = r c) r' > r 𝑽(𝐂𝐎 )𝐭 𝟐 2.4- Show that : [H3O+] t = 2 – 𝟑𝟎𝟎𝟎 where [H3O+]t is the molar concentration of hydronium ions remained at instant t and V(CO2)t is the volume of CO2 formed at the same instant t in mL. 2.5- Deduce the molar concentration of H3O+ at the half-life time of the reaction. 3- Effect of Some Factors Document-2 shows three experiments realized on the same reaction: Temperature Form and mass of CaCO3 Hydrochloric acid solution: Volume added and Concentration CA Initial rate of the reaction Experiment 1 25°C Piece (20g) Experiment 2 45°C Piece (20g) Experiment 3 25°C Piece (20g) V = 250 mL CA = 2 mol.L-1 V = 250 mL CA = 2 mol.L-1 V = 250 mL CA = 1.2 mol.L-1 r1 r2 r3 Documnet-2 3.1- Plot on the same graph of the question 2.1, the shape of the curve representing the new change in the number of moles CO2 of as a function of time: n(CO2) = g(t) of experiment 2. Justify. 3.2- Referring to the experiments 1 and 3, Compare by justifying r1 and r3. 3.3- Justify whether it is possible to compare r2 and r3. 3.4- Propose a way that permit to decrease the duration of the reaction in experiment 1 without changing the acid used and the temperature of the reaction medium. Justify. 1
