how the concentration of acid affects the rate of reaction between hydrochloric acid and calcium carbonate (magnesium ribbon)

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An investigation to find out how the concentration of acid affects the rate of reaction between hydrochloric acid and calcium carbonate
(magnesium ribbon)

Planning
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The aim of my investigation is to find out how changing the concentration of acid affects the rate of the reaction between CaCO3 and HCl. To make my experiments fair tests, I will only change one variable: the concentration of the acid. I will have to keep the volume of the acid, the mass and size of the marble chips and the temperature of the acid the same in all my experiments to insure a fair test, because by changing any of the above I will change the conditions and therefore the results will be inaccurate and the rate of reaction will be affected.

The products of the reaction between the hydrochloric acid and the magnesium ribbon are calcium chloride, water and carbon dioxide.

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

As CO2 is a gas it will escape as the reaction is taking place, therefore there will be a mass loss. Following from that I have decided to monitor this mass loss by weighing my components on a set of scales as the reaction takes place, the conical flask with the reactants will be constantly on the scales and I will be reading the mass of the display every 10 seconds. I will use 5 different concentrations of the acid. The strongest concentration will be 2 molar and the weakest will be 0.4 molar. The different concentrations will be obtained by adding a certain volume of water to the acid to dilute it this will reduce the concentration.

GRAPH

I predict that the higher concentration of the acid will have a much faster rate of reaction than the weaker solution, i.e. the mass loss will be more rapid. This is because a higher concentration of acid will contain more acid molecules per a set volume than low concentration solution. This means that there will be a higher chance of the calcium carbonate molecules colliding with the hydrochloric acid molecule and reacting.

According to the collision theory, reactant particle have to collide in order for the reaction to form a product in this case (calcium chloride, water and carbon dioxide). However not all the collisions are successful and if there is not enough energy the molecules will simply rebound.

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