An Investigation into the effect of Acid Concentration on the Rate of Reaction

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An Investigation into the effect of Acid Concentration on the Rate of Reaction

Introduction:

We are going to investigate the effect of Acid Concentration on the Rate of Chemical Reaction.  We are going to use the combination of Hydrochloric Acid and Calcium Carbonate as the reactants:

Calcium Carbonate + Hydrochloric Acid          Calcium Chloride + Water + Carbon Dioxide

Prediction

I predict that the greater the concentration of acid the greater the rate of chemical reaction i.e. the rate of reaction will be directly proportional to the concentration of acid.

This means that if I were to double the concentration of acid the rate of reaction would also double, halving the time taken.

In order to generate a more accurate picture I have constructed a series of graphs highlighting my above statements.   I have used a relative scale, following my prediction, in order to calculate the rate and therefore time taken.

This graph shows the concept of how the greater the acid concentration the greater the rate of reaction.  The idea being that with a concentration of 0 moles the rate would be infinity, comparatively by increasing the concentration of acid, the more instantaneous the reaction becomes.

 

This graph represents the relationship that exists between acid concentration and rate; by increasing the acid concentration the rate is increasing as well.  The straight line indicates the direct relationship; double the acid concentration you double the rate of reaction.

Justification

The Collision theory justifies the prediction of increased acid concentration causing increased rate of reaction by relating to the concept of proportional molecular content; i.e. if there are more acid molecules they are more likely to collide with those of the Calcium Carbonate molecules:

The diagrams above illustrate the greater likelihood of a collision in 2.0 molar concentrations due to the higher concentration of acid. We can also back this up with some maths:

If we take the reactions to have taken place in 100ml of water (different to that of my forthcoming practical) we can see that the ratio of acid molecules to calcium carbonate molecules is smallest in the 2.0 molar reactions:

If we now look at the rate of reaction we can see that is also justified by the aid of maths:

The rate was calculated using the formula of :

This enabled us to predict the time taken for the experiment

And there fore the graph of Time Taken vs. Concentration:

Just before we began to start our coursework we carried out a pilot test in order to aid us in determining what concentrations of acid we were to use.  Not only did this aid us in working out quantities for our reaction but also in adding further evidence to our prediction.  We found that the higher the concentration of acid the larger the rate of reaction, something which we had expected.  Another interesting observation was the decrease in effervescence as the acid concentration lessened- showing yet again a decrease in the rate of reaction.

Strategy

The strategy I will use to determine the rate of chemical reaction will be to measure how fast the gas will be produced;.  I will do this by timing the amount of time it takes to fill a gas syringe (to a set amount of 50cm³) from the reaction of Calcium Carbonate and Hydrochloric Acid.  In doing so we will control other factors:

This will then produce a picture representing the relationship between acid concentration and rate of reaction.

Safety

As with any experiment safety is a key issue to which we must address before starting the experiment.  Not only will it prevent harm occurring but it will also aid the fluidity to which we carryout our experiment.  Below are a few important rules that we will adhere to when performing our experiment:

· Wear Safety Goggles and Lab Coats at all times during the experiment

· No running within the laboratory

· Prevent contact with chemicals – do not taste or place them in your mouth!

· Wash your hands after handling chemicals

Method and Apparatus

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