We are going to do an experiment to see how surface area effects the rate of reaction when added to hydrochloric acid. I will add calcium carbonate (marble chips) to hydrochloric acid.
When calcium carbonate is added to hydrochloric acid a reaction takes place. The solution fizzes and gives off the gas carbon dioxide. I will collect this gas in a gas syringe and will time how long it takes for the reaction to produce 100cm3 of carbon dioxide.
CaCO3 +2HCL Co2 +CaCl2 +H2O
I predict that when the small marble chips are added to the hydrochloric acid the rate of reaction will be faster and therefore will result in more gas (carbon dioxide) being given off. This is because the small marble chips have a larger surface area. When the large marble chips are added to the hydrochloric acid the rate of reaction will be slower resulting in less gas being produced. This is because the large marble chips have a smaller surface area. This means that it will be quicker with the smaller marble chips to produce 100cm3 of carbon dioxide.
This is all due to the collision theory which states that for a chemical reaction to happen the reactants must first collide with each other. However, just colliding is not enough. For a reaction to take place, the reactants must collide with enough energy. If more surface area is available, the number of particles of the solid reactant available will increase. If more collisions occur, it is likely that there will be more collisions with sufficient energy to successfully lead to a reaction.
When the marble cube is split up, more of its surface area can react with the acid.
Temperature also effects the rate of reaction because at a higher temperature, the faster moving particles have more kinetic energy. This means they will collide more often therefore the number of effective collisions will increase.
Before we undertook our full experiment we needed to carry out a preliminary experiment. This is because we needed to check that our experiment will work and that reaction did not go too fast or too slow. I needed to see what concentration the acid needs to be so that I can collect at least six readings so that I can make a firm conclusion.
In the preliminary experiment we used hydrochloric acid that had a concentration of two molar (2.0M). We needed to see if this concentration was suitable to get enough readings. We added 30ml of 2.0M hydrochloric acid to the 3g of small marble chips. We put the bung on the conical flask and started a stopwatch. The reason what we used small marble chips is because according to the collision theory they have the largest surface area and should therefore have the quickest rate of reaction.
The reaction between the 2.0M hydrochloric acid and the small marble chips was too quick. Within 30 seconds over 100 cm3 of CO2 was produced. This meant that a second preliminary experiment had to take place. This time we used the same amount of marble chips and hydrochloric acid but instead using a concentration of 1.0M. I diluted the acid by adding 20ml of water to 20ml of acid. I discovered that I could take six readings, which would be enough to make a firm conclusion. So I will use 1.0M acid in my experiment as I know I can get at least six readings.
To make this test fair I will keep everything the same and only change one thing at a time.
I will only change the size of the marble chips from large to medium and then small.
The things that I will keep the same are:
-same mass of calcium carbonate each time. (3.0g)
-Same volume of hydrochloric acid (30ml)
-Keep the temperature the same
-Keep the same concentration of the acid
Precision and Reliability
-Use measuring cylinders to measure acid accurately.
-Use gas syringe to measure the volume accurately.
-Keep record of...
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