# Experiment Plan. Effect of Surface Area on Rate of Reaction

by rbchen (student)

Horizon International School

School code: 006048

Session: May 2013

Candidate name: Zwe Kyaw Zwa

Candidate number: 006048-004

Subject level: Higher Level

Assessment

Research Question

How does the surface area of calcium carbonate (CaCO3) affect the rate of reaction with dilute hydrochloric acid (HCl)?

Hypothesis

The rate of reaction of calcium carbonate with a larger surface area will be faster than that of calcium carbonate with a smaller surface area.

Background Theory

To determine the effect of surface area on the rate of reaction, a known mass of calcium carbonate granules and powder are each placed in a flask, into which standard dilute hydrochloric acid is added. An acid reacts with a carbonate to give a chloride, water and carbon dioxide. Over time, the mass of calcium carbonate decreases while the volume of gas, carbon dioxide, increases. The more gas that is produced in the reaction, the faster the reaction is occurring.This can be measured by means of a graduated gas syringe. The reaction can be represented by the equation:

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

The results of the two reactions are plotted on the same axes of a graph of volume of CO2 produced against the time taken. The gradient of the curves are used to judge the rate of the reaction; the steeper the slope, the faster is the reaction. The time taken to reach the end of reaction (curve to become horizontal) also indicates the speed of the reaction; the less reaction time needed, the faster is the reaction.

Since the concentration of HCl(aq) and mass of CaCO3 are constant, the volume of CO2 produced is constant. However, the more finely divided a solid is, the larger is its surface area. According to the collision theory, the rate of a reaction is directly proportional to the number of effective collisions per second between the reactant molecules. Increasing the surface area increases the number of effective collisions per unit time. Therefore, powdered calcium carbonate reacts much faster with dilute hydrochloric acid than if the same mass is present as granules of marble or limestone.

Variables

Independent Variable:                Size of ...