What Effect Will the Concentration of Hydrochloric Acid Have on the Rate of Reaction Between Hydrochloric Acid and Magnesium?

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In this chemical reaction, the magnesium will dissolve in the hydrochloric acid to produce hydrogen gas. This is because magnesium is higher than hydrogen in the reactivity series. Therefore, when the two reactants are combined, a displacement reaction occus and the magnesium displaces the hydrogen, forming magnesium chloride and hydrogen gas.

Mg (s) + 2HCl (aq) -> MgCl 2 (aq) + H 2 (g)

Magnesium + Hydrochloric acid -> Magnesium Chloride + Hydrogen


The aim of this investigation is to observe the effect that the concentration of hydrochloric acid (independent variable) has on the rate of reaction (dependent variable) between the magnesium ribbon and the hydrochloric acid.


As the concentration of hydrochloric acid increases, the time taken for the magnesium to disappear will decrease. (The greater the concentration of hydrochloric acid, the faster the reaction between the magnesium and hydrochloric acid will occur.) In addition, doubling the concentration of hydrochloric acid will halve the time taken for the magnesium ribbon to disappear. This hypothesis is based on the collision theory. The collision theory states that for a chemical reaction to occur, there is a minimum amount of energy that must be provided by the colliding particles in order to break or form new bonds with other particles. When the bonds are broken this is called a successful collision. If the minimum amount of energy (also known as activation energy) is not provided, the particles will simply bounce off each other causing an unsuccessful collision. Applying this theory to the hypothesis, a greater concentration would mean there would be more particles in the same volume. A greater amount of particles would result in more collisions, and therefore a higher chance for successful collisions to occur, resulting in a faster chemical reaction since more bonds are being broken. Therefore a higher concentration of hydrochloric acid should result in a faster chemical reaction. In addition, theoretically, if there are twice as many particles in the same amount of volume, there will be twice the amount of collisions, and double the chance of successful collisions occurring, therefore the rate of reaction should be twice as fast.

Main Variables

Independent Variable: The concentration of hydrochloric acid, which is made by diluting the HCl with water. Starting from a solution consisting of 10ml of HCl and 40ml of water, and adding 10ml of HCl and taking away10ml of water from the previous solution for each new trial.

Concentration of HCl (%)Amount of HCl (ml)Amount of H 20 (ml) Trial 1201040
Trial 2402030
Trial 3603020
Trial 4804010
Trial 5100500

Dependent Variable: The rate of reaction. (Using the average of the results obtained, the rate of reaction can then be studied by drawing graphs with the volume of gas produced (cm^3) as the dependent variable and the time (seconds) as the independent variable. A tangent should then be drawn to each of the curves at 45 seconds, and the gradient should then be worked out afterwards using trigonometry: tangent x = opposite (cm^3) / adjacent (seconds). This will enable us to compare the rate of reaction of different concentrations of hydrochloric acid when reacted with magnesium ribbon.)

Fair Test:

- Temperature:

Ensure that the temperature the experiment is conducted in is the same for each trial. In this experiment, all trials will be conducted at room temperature. Increasing the temperature will provide more kinetic energy to the particles in the HCl, allowing for more collisions to occur, and thus more successful collisions. There will be more successful collisions also because the amount of kinetic energy provided by the increase in temperature would more likely be greater than the activation energy needed to break the bonds for a chemical reaction, thus increasing...
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