CaCO3 (s) + 2HCI (aq) CaCI2 (l) + CO2 (g)
My prediction is that the higher concentration of the acid, the faster rate of reaction. This is because a higher concentration of acid will contain more acid molecules per a set volume than a low concentration solution. This means that they will be a higher chance of calcium carbonate molecules colliding with the hydrochloric acid molecules and reacting.
According to the collision theory, reactant particles have to collide in order for the reaction to form a product in this case (calcium chloride, water and carbon dioxide). However not all collisions are successful and if there’s not enough energy, the molecules will simply rebound. When the concentration is high, there are more collisions and therefore a bigger chance of collision being successful.
The rate of the reaction is directly proportional to the concentration
of the acid. For example, doubling the concentration of the acid will double the rate of reaction
The reaction rate, however, should theoretically decrease as the reaction between HCI and CaCO3 progresses; this is because as the reaction time increases the number of HCI molecules present will decrease as they react with CaCO3 molecules to produce calcium carbonate, water and carbon dioxide. Although carbon dioxide escapes into the air, the water produced will dilute the hydrochloric acid even further, so the concentration will go down, as there will be less successful collisions, as there will be less HCI molecules. This should therefore make the graph a curve and not a straight line. This is because the mass will not be changing at a constant rate.
This is why I am going to carry out each experiment for 60 seconds to avoid one or more reactants running out. This is how I predict my graph to look like with its line of best fit.
However if I don’t do 60 seconds each test, my graph will bend into a straight line which will end up looking like this. This means that the reaction has stopped because one or more reactants have run out.
This reaction is an exothermic reaction and therefore the energy produced in the reaction will be needed to break old bonds in CaCO3 and HCI, and make new bonds in CO2, H2O and CaCl2. The atoms have to be broken loose from their arrangements and re-arranged with new bonds in to new substances.
For this experiment, I am going to need the following apparatuses
This is my method:
- Collect all equipment.
- Measure out the marble chips and the hydrochloric acid.
- Place the acid and then the marble chips into the conical flask very quickly and sharp.
- Put on your timer to see how long it takes to get to 20cm3.
- Record the results and repeat the experiment again changing the amount of acid and water.
- Record results in a table.
Everything will be kept the same to insure fair test. The size of the marble chips, the temperature of the acid and the mass of the chips will be kept the same.
To make it a safe test, I will wear goggles to protect my eyes in case of the acid spilling. I will also have to handle the glassware very carefully when carrying it around so that it doesn't smash.