March 5, 2010
Internal Assessment – Investigating the relationship between concentration of reactants and rate of reaction using hydrochloric acid and magnesium strip
To study the effect of manipulating the concentration of hydrochloric acid on the rate of hydrogen gas production during the reaction with magnesium, using the pressure buildup by hydrogen gas. Introduction
Concentration and surface area of reactant, temperature, and catalyst are the factors that affect the rate of a reaction. In this experiment the reaction between hydrochloric acid solution and magnesium ribbon is used to investigate the effect of reactant concentration on the rate of reaction. The concentration of hydrochloric acid is manipulated using serial dilution.
Rate of reaction can be calculated by measuring the speed at which reactants are consumed or the speed at which products are formed. Since gas is produced in this reaction, rate of reaction can be determined by the change in pressure as reaction proceeds. The pressure inside the test tube in which the reaction occurs is measured every second over 70 seconds using a gas pressure sensor. The rate of reaction at differing concentration is obtained by calculating the slope of time vs. pressure graph, since rate of reaction is change in pressure over time. If the change of pressure is significant the rate of reaction is high and if the change is small the rate is low.
The collision theory must be used to study the relationship between concentration of a reactant and the rate of reaction. The collision theory states that in order for a reaction to occur, two particles involved must
collide with each other
the collision must be energetic enough to overcome the activation energy of the reaction the collision must occur with the correct geometrical alignment, bringing the reactive parts of the molecules in contact
Based on the collision theory, as the concentration of hydrochloric acid solution increases (which means that the number of hydrogen and chloride ions increase), the chances of magnesium particle colliding with the hydrochloric acid particles at a given time period also increase. Increase in the overall number of collision would increase the number of effective collisions, although the ratio between effective and noneffective collisions would stay constant. As such, the hypothesis for this experiment is the higher the concentration of hydrochloric acid, the higher the rate of hydrogen gas production.
March 5, 2010
Method of measuring/ controlling
The pressure is measured using gas
pressure sensor. The pressure of the test
tube only during initial 70 seconds is
measured to find the change in pressure.
Pressure inside the test tube
To reduce random error three
measurements are made for each
concentration of hydrochloric acid
Rate of reaction
Concentration of hydrochloric acid
Using 1M hydrochloric acid solution, a
serial dilution is performed to obtain
solutions of 08M, 0.4M, 0.2M, 0.1M
and 0.05M concentration, using a pipette
( ± 0.040
) and volumetric flask ( ±
Length of magnesium ribbon
2cm of magnesium ribbon is used each
trial. The length is accurately measured
using a ruler.
Size of the test tube
The rate of reaction is calculated by
dividing the change in pressure over a
certain period of time. Thus in the
pressure vs. time graph the slope is the
rate of reaction.
The size of the test tube used should be
constant since change in volume would
also change the pressure inside the
container for the same amount of gas. A
small sized test tube is preferred since
using a large sized container would
require a longer time for the pressure to
Volume of hydrochloric acid solution
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