How does changing the concentration of acid affect the rate of reaction between hydrochloric acid and calcium carbonate?

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How does changing the concentration of acid affect the rate of reaction between hydrochloric acid and calcium carbonate?

Introduction

During any chemical reaction the concentrations of the reactants decrease and the concentration of products increase with time. The rate of reaction (reaction velocity) may be defined as the rate of change of concentration of a stated reactant or product. The rate of a reaction is found by measuring the amount of a reactant used up per unit of time or the amount of a product produced per unit of time. A reaction can be made to go faster or slower by changing a number of factors. In order for a reaction to occur it is necessary that: particles must collide with each other and the collision must have enough energy. If this happens the original bonds are broken and new bonds are formed - so that new products are formed. Successful collisions (those with sufficient energy) can be increased (or decreased) by a number of factors. The rate of reaction can be changed in four ways: -

Ø Altering the surface area of the reactants

Ø Changing the concentration/pressure of the reactants

Ø Altering the temperature at which the reaction takes place

Ø Using a catalyst

My experiment is going to assess how the concentration of the acid affects the rate of reaction.

The more concentrated the solvent, the more particles are present and the greater the chance of a successful collision. In dilute acids, with fewer particles the chance of successful collisions occurring is reduced. Therefore if concentration is increased, the reaction rate also increases. This also applies in reactions between two gasses when increasing the pressure has the same effect as increasing the concentration. I am going to use acid of 0.1M, 0.25M, 0.5M, 1.0M and 2.0M. This will give me a good range of results. I intend to collect results by finding out how much carbon dioxide (a product of the reaction) is produced in relationship with time.

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Fair Testing

In order to carry out a fair test the only variable I will change is the concentration of the acid. I will ensure that the following variables are kept constant:

Ø Surface area of solute (marble chip)

Ø Amount of reactants (5g of marble chips and 20cm3 of hydrochloric acid)

Ø Catalyst (no catalyst will be involved)

Ø Temperature (room temperature throughout)

A fair test will also require the experiment to be repeated several times at each temperature for reliable results.

Since I will be working with strong acid, I will wear safety goggles while conducting the experiment.

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