How does the concentration of HCl affect the rate of reaction with CaCO3?

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Tinaye Mandishona

Chemistry Investigation – How does concentration affect rate of reaction?

In this experiment we are looking at how concentration affects rate of reaction. We are reacting 0.5 grams of marble (CaCO3) with different concentrations of hydrochloric acid (HCL- 0.25 molar – 1.5 molar). When you react marble (CaCO3) with Hydrochloric acid (HCl) you produce Calcium Chloride (CaCl2), Carbon dioxide (CO2) and water (H2O).

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


Control variables:

  • Temperature – temperature can increase the rate of reaction so in our experiment we are going to try keep the temperature the same (will be explained in more detail how it affects rate of reaction in the bottom half of introduction).
  • Surface area – If we increase the surface area of our reactants we increase the rate of reaction so therefore we will keep the surface area of the reactants the same (will be explained in more detail how it affects rate of reaction in the bottom half of introduction).
  • Time – We are keeping the time at 1 minute because we used powdered marble so the reaction went very fast because the surface area was very large therefore we decided to make time one of our control variables.
  • Catalysts – We are not adding any catalyst to our experiment, this is to see how our independent variable has an effect by itself on the rate of reaction.

Dependant variable-

  • Volume of carbon dioxide produced – we measured the amount of carbon dioxide produced because this was the only product made that we were able to extract with the equipment we were given.

Independent variable-

  • Concentration – We decided to make our independent variable concentration because we found it more manageable to test and we were not allowed to use catalysts.

Collision theory explains why chemical reactions occur and why they react at different rates. It was proposed by Max Trautz and William Lewis in 1916 and 1918. A reaction can only take place if the reactant particles collide; also the force in which they collide has to be stronger than the bonds of the reactant particles. The activations energy (energy required for a reaction) has to be stronger than the bonds so that they break the bonds and form new one to make new particles (products). Chemical reactions can either be successful or unsuccessful, successful chemical reactions only take place when successful collisions happen; successful collision only happens when the activation energy is stronger than the bonds.

Rate of reaction is how fast/slow a reaction is. There are many factors that can affect the rate of reaction:

  • Temperature – temperature affects rate of reaction because when you increase the temperature you cause the particles to vibrate causing them to move about more and this increases the chances of the reactant particles colliding also they give the particles more energy lowering the activation energy so the particles can react easier.
  • Catalyst – Catalyst are substances that speed up chemical reactions without getting used up. Catalysts increase the number of successful collision by creating another way for the chemical reaction to react with lower activation energy. They provide lower activation energy by either breaking the bonds of the reactant materials so that the activation energy decreases or makes them come closer together so they can collide together and react more frequently.
  • Concentration & Pressure- Concentration increases the rate of reaction because if you increase the concentration you increase the number of reactant particles that could collide in a given area, so there would be more collision occurring. The same thing happens in pressure, you increase the amount of reactant particles in a given space so there are more collisions likely to happen.

  • Surface area- You can increase surface area by making solids into powders by crushing or grinding them, this allow more of the other reactant particles to react with powdered reactant particles because there would be more area for the other reactant to attack, but if the reactant was a solid the other reactant could only attack the other layer, slowly working its way through it, so by increasing the surface area you increase the rate of reaction!
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You can work out rate of reaction by either doing amount of product produced divide by time or 1000/time to give you the rate of reaction per 1000th.

Preliminary write up

List of apparatus:

  • 0-100 ml Measuring cylinder – we used this to measure how much carbon dioxide was produced.
  • Burette (replaced the measuring cylinder) – we used this to measure how much carbon dioxide was produced.  
  • Pipette – we used a pipette to put hydrochloric acid into the 10ml measuring cylinder because it helped us put the hydrochloric acid exactly to the 10 ml.
  • 0-10 ml ...

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