KINETIC-SV

1
Experiment 1
Experiment 2
Experiment 3
Temperature
25°C
45°C
25°C
Form and mass of CaCO3
Piece (20g)
Piece (20g)
Piece (20g)
Hydrochloric acid solution:
Volume added and
Concentration CA
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
Initial rate of the reaction
r1
r2
r3
Documnet-2
t (s)
10
20
30
40
60
80
100
120
n (CO2) (10 – 2 mol)
3.0
5
7
8.75
11.25
13.25
14.75
15.5
Document-1
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:
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
2.4- Show that : [H3O+] t = 2 – 𝑽(𝐂𝐎𝟐)𝐭
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:
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.