Fair Test
In order to make my experiment safe I will change only one thing. I will be changing the concentration of the acid. Everything else will remain the same through out the experiment. I will use the same equipment and do the experiment during the same lesson where I can. This can be important because room temperature can increase the rate of reaction. The temperature could be higher on a certain day and affect my results.
Background Information
Rates of Reaction
- Increasing the temperature increases the rate of a chemical reaction.
- Some chemical reactions are fast and others are slow. A fast reaction could be a rocket exploding, and a slow reaction is metal rusting.
- Rates of reaction can be measured by finding out how quickly a product is formed or how quickly a reactant is used up.
- Examples of measuring reaction rates include measurement of the volume of gas formed, and measurement of the loss in mass when a gas is given off.
How does surface area affect a chemical reaction?
If one of the reactants is a solid, the surface area of the solid will affect how fast the reaction goes. This is because the two types of molecule can only bump into each other at the liquid solid interface, i.e. on the surface of the solid. So the larger the surface area of the solid, the faster the reaction will be.
Smaller particles have a bigger surface area than larger particle for the same mass of solid. There is a simple way to see this. Take a loaf of bread and cut it into slices. Each time you cut a new slice, you get an extra surface onto which you can spread butter and jam. The thinner you cut the slices, the more slices you get and so the more butter and jam you can put on them. This is "Bread and Butter Theory". By chewing your food you increase the surface area so that digestion can go faster.
The effect of Surface Area – Solid particle size
- If a solid reactant or a solid catalyst is broken down into smaller pieces the rate of reaction increases.
- The speed increase happens because smaller pieces of the same mass of solid have a greater surface area compared to larger pieces of the solid.
- Therefore, there is more chance that a reactant particle will hit the solid surface and react.
- The diagrams below illustrate the acid-marble chip reaction.
Forces that change the rate of reactions
Reactions happen, no matter what. Chemicals are always combining or breaking down. There are a few things which really affect the speed of the reaction and the number of collisions that can occur.
(1) Concentration: If there is more of a substance in a system there is a higher chance that molecules will collide and speed up the rate of the reaction. If there is less of something, there will be fewer collisions and the reaction will probably happen at a slower speed.
(2) Temperature: When you raise the temperature of a system the molecules move around a lot more (because they have more energy). When they move around more they are more likely to collide. That means they are also more likely to combine. When you lower the temperature the molecules are slower and collide less. That temperature drop lowers the rate of the reaction.
(3) Catalyst: A catalyst is a substance that alters the rate of a chemical reaction without being used up or permanently changed chemically. A catalyst works by changing the energy pathway for a chemical reaction. It provides an alternative route (mechanism) that lowers the Activation Energy meaning more particles now have the required energy needed to undergo a successful collision.
Equipment
Beaker
Measuring cylinder
Delivery tube with bung
Water Tray
Marble chips
Hydrochloric acid: 0.5 molar to 3.0 molar
Top-pan balance
Safety goggles
Stopwatch
Water
Paper towels
Prediction
I will be changing the concentration of the acid and not the size of the marble chips during my experiment. From looking at my background information and my knowledge of reactions I predict that the larger the concentration of the marble chips, then the quicker the reaction will be. This happens because there is more of the reactant which comes in contact with the acid causing a quicker reaction.
Although I predict that the larger chips will react quickest, I believe that the medium marble chips and a molar of 2.5 will be the quickest and most effective. This is because if I use 3.0 molar acid with large marble chips, the reaction will be too quick to record.
Safety
I will be using acid during this experiment, therefore I will be wearing safety goggles. I will stand up when doing the test and leave all bags under the table and out of the way.
Conclusion
I feel my experiment went very well with no major incidents. A few things that I could have changed are:
- Taken more care with the water as there were spillages.
- Measured out the exact amount of grams of marble chips, because I could not always measure the same amount on every experiment.
My results were scientifically correct and matched my prediction.
