The Effect of the Concentration of Sulphuric Acid on the
Reaction Rate with Magnesium
April 1, 2009
The nature of the problem is to design an investigation that examines a variable affecting the reaction rate. In this experiment, magnesium will be reacted with different concentrations of sulphuric acid. The reaction is shown by the following chemical equation: H2SO4 (l) + Mg (s) → MgSO4 (aq) + H2 (g)
This equation shows that when magnesium is combined with sulphuric acid, the magnesium dissolves in the acid to form an aqueous solution containing Mg (II) ion and hydrogen gas.
Sulphuric acid (H2SO4) is a strong corrosive acid that is made from sulphur dioxide. It is commonly used in lab experiments and in the chemical industry (Faiers). Magnesium (Mg) is an alkaline earth metal which is solid at room temperature. When it reacts with an acid, it produces hydrogen gas and a salt. The hydrogen gas produced by this reaction is what will be measured in this investigation.
The rate of reaction is defined as how fast a reaction takes place (Parry). There are certain factors which affect reaction rates, including the temperature of the reactants, the surface area of the reactants, the concentration of the reactants, and the presence of a catalyst. According to the collision theory, effective collisions between particles are needed in order for the reaction to take place (Neuss). By increasing the concentration of the solution, the number of effective collisions between the particles will also increase. This will produce more product (hydrogen gas).
The concentration is the amount of substance contained within a given volume of a solution (Green & Damji 33). This is given as the number of moles of the substance in one cubic decimetre (equivalent to 1 litre). This can further be expressed in the following formula: Concentration (mol· dm-3) =
By increasing the amount of solute in the solution, the collision rate increases, therefore increasing the rate of reaction.
Figure 1 shows how increasing the concentration of solute increases the amount of effective collisions between the particles, resulting in a greater reaction rate. In this experiment, the independent variable is the change in concentration of the sulphuric acid. The dependant variable is the amount hydrogen gas produced in thirty seconds. The hydrogen gas was measured using a gas displacement technique. There is no control situation due to the nature of the experiment. The concentrations of sulphuric acid that will be used are 0.2 M, 0.3 M, 0.4 M, 0.5 M and 0.6 M. These concentrations were obtained by adding different amounts of water to 17.25 M sulphuric acid. The equation C1V1=C2V2 was used to calculate the amount of H2SO4 and water needed for each trial. To increase the accuracy of the results there are many variables that need to be kept constant. These include the volume of the solution, which will be kept constant at 50 cm3. The temperature of the reactants will be kept at room temperature. The mass of magnesium used will be carefully measured to be 0.2 g for each trial. The amount of time for each experiment will be kept constant at thirty seconds, using a stopwatch. Also, the same equipment will be used for the entirety of the investigation in attempt to obtain the most accurate results. Based on the research, it can be predicted that the reaction rate between sulphuric acid and magnesium will increase as the concentration of sulphuric acid increases. Hypothesis
If the concentration of sulphuric acid is increased, then the reaction rate with magnesium will also increase. Materials
• 50 cm3 of 17.25 M sulphuric acid
• 3 g of powdered magnesium (± 0.05 g)
• 100 cm3 gas burette (± 0.05 cm3)
• Retort stand
• 200 cm3 Erlenmeyer flask
• 100 cm3 graduated cylinder (± 0.2 cm3)
Cited: Faiers, A. Kinetics. Mar. 2009. Chemistry in Perspective. Jan. 2008. .
Green and Damji. Chemistry. Victoria: IBID Press, 2007.
Neuss, Geoffrey. Chemistry for the IB Diploma: Study Guide. New York: Oxford University Press, 2007.
Parry, R.. Chemistry Experimental Foundation. Boston: Prentice Hall College Div., 1982.
Amount of solute (mol)
Solution volume (dm3)
Figure 1: Concentration of Solute
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