An Investigation to determine the factors which affect the rates of reaction between Marble Chips (CaCO3) and Hydrochloric Acid (HCl)

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   An Investigation to determine how acidic concentration will affect the rate of reaction between Marble Chips {Calcium Carbonate} (CaCO3) and Hydrochloric Acid (HCl)

In my investigation I want to determine the factors which will affect the rate of reaction between marble chips and hydrochloric acid, and how a certain factors affect the rate of reaction when CaCO3 is reacted with an excess of HCL.

Rates of reaction are based on the collision theory, and the collision theory states that the following must happen for a reaction to take place:

        i)        firstly a collision must take place between two reacting particles.

ii)        and a reaction will only result if the two colliding particles posses enough activation energy to react, otherwise they will just bounce off.

The Equations:

The equation of the reaction between marble chips and hydrochloric acid is shown below:

Marble Chips + Hydrochloric Acid                 Calcium Chloride + Water + Carbon

(Calcium Chloride)                                                   Dioxide

CaCO3 (s)      + 2HCL (aq)                CaCl2 (aq)             + H20 (l) +  CO2 (g)

The Experiment:

The way that we can calculate the rate of reaction is if we plot the initial rate of reaction against the variable. And the way that we can calculate the rate of the reaction is if we collect one of the waste products of the reaction, and for this reaction between marble chips and hydrochloric acid the waste product that I am going to collect will be Carbon Dioxide.

There are two ways that I could collect and measure the carbon dioxide produced from the experiment.

Gas Syringe:

This measure the volume of gas given off by the experiment:

Scales:

The scales measures the amount of mass lost during the reaction as the gas is given off.

Following a set of preliminary experiments I found that the best method to collect the gas given off was the scale method, as there was no need to read off a scale, this meant that it reduced the probability of human error. And hence give more accurate results. The gas syringes only measured up to 100 cm3 and this meant that the gas syringe had to be reset, and this meant that some of the gas escaped whilst the equipment was being reset and hence the probability of recording accurate results was reduced. So all in all the scale method is the best method of collecting the gas being produced by the reaction.

Possible variables:

There are a number of variables I could chose to use in my experiment and they are listed below:

Particle Size:

 The rate of reaction between an acid and a carbonate can be greatly increased by making the carbonate a powder rather than lumps. As the surface area of the particles is greatly increased and hence there are more chances for the acid particles to successfully collide with the carbonate particles

A large particle means that there is a smaller surface area, hence less chances of a successful collision.

Figure 1:

Many small particles means that the total particles have a larger surface area, hence more chances of a successful collision.

Figure 2:

Concentration of the hydrochloric acid:

If there is a greater concentration of any of the reactants present, then the probability of a collision between each particle is increased

Low Concentration of particles hence there is a low rate of collisions

 

Figure 3:

High Concentration of particles hence a high rate of collisions.

                                        

Figure 4:

N.B Not all the collision will result in a reaction, but with a greater rate of collisions the probability of a success full collision increases.

Temperature:

The rate of many chemical reactions usually doubles for every 10oC rise in temperature. As the temperature increases the more energy is given to the particles, thus enabling them to move about more vigorously with more energy. It also makes them collide more regularly. These two factors rapidly increase the rate of successful collisions and the rate of reaction increases rapidly.

Fair Testing:

To ensure that my experiment is a fair experiment I shall implement the following ideas:

  • always using the same volume of acid

  • attempting to ensure that in every experiment the size and surface area of the marble chips remains constant

  • ensuring that the conical flask is thoroughly cleaned after each experiment to ensure that no ‘cross contamination’ takes place

  • attempting to ensure that all experiments take place in similar conditions, i.e. room temperature, moisture etc.

Preliminary Experiment:

The aim of the preliminary experiment was to determine the right concentration range, marble chip size (Large, Medium or Powdered), the correct procedure and the optimum mass of the marble and volume of the acid.

The results of the preliminary experiment are shown in the graphs below.

N.B Both experiments use 50 cm3 of acid

Looking at the first graph it is clear that the rate of reaction is greater with 10g than with 7.5g. And looking at the second graph we see that the powdered chips get ‘used’ too quickly hence the reaction tapers off at the end. And the large chips are very slow to react. Therefore I will choose to use 10g of medium sized marble chips. Also I see no problem with using 50 cm3 of HCL, as all the reactions reacted perfectly well with that volume of acid.

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Looking at the graph it is clear that the reaction is faster with medium chips, but the data collected is much more erratic than with the large chips. But all in all I think I will choose to use the medium chips. Also both sets of marble chips were able to react with 0.2 M HCL; hence I have found the two limits of my concentrations, 2M and 0.2. I have also decided that the optimum mass and type of the marble chips is 10g of medium sized chips.

Experimental Variable:

For my investigation I ...

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