PEKA Chemistry form 5 chapter 1 (To study the effect of the size of marble chips, CaCO3, on the rate of the reaction.)

Aim                             : To study the effect of the size of marble chips, CaCO3, on the rate of the                                           reaction.

Problem statement      : How does the size of marble chips, CaCO3, affect the rate of reaction?

Hypothesis                  : When the size of marble chips, CaCO3, is smaller, the rate of reaction increases.

Variables                     :-

                                    Manipulated variable  : Size of marble chips, CaCO3.

                                    Responding variable   : Rate of reaction.

Controlled variables   : Volume and concentration of hydrochloric acid, HCl, mass of marble chips

Operational definition : The changes of gas volume are measured in intervals of 30 seconds when marble chips, CaCo3, added to hydrochloric acid, HCl.

Smaller marble chips have a larger total exposed a\surface area than larger marble chipsof the same size.

Apparatus                    : 50cm3 measuring cylinder, 100cm3 conical flask, rubber stopper with delivery tube, basin, burette, electronic balance, retort stand with clamp, stopwatch

Materials                     : 0.1 mol dm-3 hydrochloric acid, HCl, water, small and large marble chips, CaCO3

Procedure                    :-

1.      40cm3 of 0.1 mol dm-3 hydrochloric acid, HCl, is measured with a measuring cylinder and the poured into the conical flask.

2.      2g of large marble chips, CaCO3, (Set I) is weighed with a electronic balance.

3.      The basin and the burette are filled with water. The burette is inverted in the basin and clamped vertically with a retort stand.

4.      The water level in the burette is adjusted so that the reading of the water level is almost at 50cm3.

5.      The apparatus are set up as shown in the figure.

6.      Pour the of large marble chips, CaCO3, that have been weighed into the conical flask which filled with hydrochloric acid, HCl.

7.      Immediately, the conical flask is covered with a rubber stopper which is joined to the delivery tube. The gas released been channeled into the burette and the stopwatch is started at the same time.

8.      The conical flask is shaken slowly throughout the experiment.

9.      The burette readings are recorded at intervals of 30 seconds for 5 minutes.

10.  Steps 1 to 9 are repeated by replacing the 2g of large marble chips, CaCO3, (Set I) with 2g of small marble chips, CaCO3, (Set II) whereas the other conditions remain unchanged.

11.  The results are recorded in a table.

12.  The volume of carbon dioxide, CO2, gas collected are measured.

Data and observations            :-

Interpreting data         :-

1.      Based on the results, a graph of the total volume of carbon dioxide gas, CO2 collected against time for sets I and II is drawn on the same axis.

2.      Based on the graph plotted, determine 

(a)    The overall average rates of reaction for

(i)                 Set I

(ii)               Set II

(b)   The rates of reaction at

(i)                 60th second

(ii)               90th second

For sets I and II.

3.      Compare the rates of reaction for both sets of experiments.

4.      Deduce the effect of the size of a solid reactant on the rate of reaction.

Discussion                   :-

           

1.      What is the relationship between the size of the marble chips, CaCO3, and the total surface area of ​​marble chips, CaCO3 that is exposed to the reaction?

-          A smaller the size of the marble chips, CaCO3, has a larger total exposed surface area.

2.      What is the relationship between the total surface area of marble chips, CaCO3 and the rate of reaction?

-          The larger the total surface area, the higher the rate of reaction.

3.      Write down the chemical equation for the reaction between marble chips, CaCO3 and hydrochloric acid, HCl.

-          CaCO3(s) + 2HCl(aq) à CaCl2(aq) + H2O(l) + CO2(g)

4.      Calculate the expected maximum volume of carbon dioxide, CO2 that should be collected in both sets I and II.

(Molar volume of gas: 24 dm3 mol-1 at room conditions. Relative atomic mass: C, 12; O, 16; Ca, 40)

-          48cm3

5.      Compare the maximum volume of carbon dioxide, CO2, gas collected in the burette with the expected maximum volume of carbon dioxide, CO2.

-          The volume of carbon dioxide, CO2, gas collected in the burette is less compared to the expected maximum volume of carbon dioxide, CO2, gas.

6.      Explain why there is difference between the volumes of carbon dioxide, CO2.

-          The volume of carbon dioxide collected from the experiment is less compared to its theoretical value. This is due to small amounts of carbon dioxide dissolving in the water.

7.      Suggest a method to overcome the difference between the volumes of carbon dioxide, CO2.

-          To overcome this problem, the water in the burette must be first be saturated with carbon dioxide by passing the gas through the water a few minutes before starting the experiment.

Conclusion                  : Hypothesis accepted. When the size of marble chips, CaCO3, is smaller, the rate of reaction increases.