Background Knowledge: Rate is a measure of how fast or slow something is. For example, Silver Chloride precipitating (this is a very fast reaction) and Concrete setting (it may take a couple of days for concrete to harden). Rate is a measure of the change that happens in a single unit of time. Any suitable unit of time can be used - a second, a minute, an hour and even a day. To find the rate of reaction, you should measure: The amount of reactant used up per unit of time or the amount of a product produced per unit of time. We are going to do an experiment on the rate of reaction.
We are using acid and magnesium strips to test the rate of reaction. Rates of reaction can be varied by a number of factors: The concentration of the acid in which the magnesium is placed, The temperature of the acid and The size of the surface area of the magnesium strip. Why rate changes with concentration If the concentration of the acid is increased, the reaction goes faster. 1 2 - Acid Particle - Water Molecule - Magnesium Atoms 1. In dilute acid, there are not so many acid particles. This means there is not much chance of an acid particle hitting a magnesium atom.
2. Here the acid is more concentrated - there are more acid particles in it. There is now more chance of a successful collision occurring. The more successful collisions there are the faster the reaction.
This idea also explains why the reaction between magnesium and hydrochloric acid slows down as time goes on: 1 2 - Acid Particle - Water Molecule - Magnesium Atoms 1. At the start, there are plenty of magnesium atoms and acid particles. But they get used up during successful collisions. 2.
After a time, there are fewer magnesium atoms, and the acid is less concentrated. So the reaction slows down. Why rate changes with the temperature low temperatures particles of reacting substances do not have much energy. However, when the substances are heated, the particles take in energy. This causes them to move faster and collide more often. The collisions have more energy, so more of them are successful.
Therefore the rate of reaction increases. Why rate increases with surface are aThe reaction between the magnesium and acid is much faster when the metal is powdered: 1 2 - Acid Particle - Water Molecule - Magnesium Atoms 1. Acid particles can collide only with magnesium atoms on the outside of the metal. 2. When the metal is powdered, many more atoms are exposed. So there is a greater chance of successful collisions.
For my experiment my independent variable will be the concentration of the acid. I chose this as my independent variable as I feel this is the safest and easiest way to carry out the experiment. If I was to choose the temperature of the acid as my independent variable, and if I were to heat the acid too much it may boil and produce a corrosive gas, which would life threatening. It would be difficult to work out an accurate reading of the surface area if I was to choose the surface area as my independent variable.
Variables: INDEPENDANT VARIABLE: My independent variable is the concentration of the acid. CONTROLLED VARIABLE: My controlled variables are the temperature of the acid, the size of the surface area of the magnesium, the volume of the acid / water solution and the length of the magnesium strip. DEPENDANT VARIABLE: My dependant variables are the volume of the magnesium and the mass of the magnesium. Apparatus: Stop Clock -Water - Acid -Test Tube rack - Test Tube -Magnesium - Ruler - Scissors - Beaker - Measuring Cylinder -Safety: Safety is a very important part of this experiment as we are working with a corrosive chemical that is very dangerous. When carrying out the experiment, be sure to wear safety goggles as we are working with acid.
When measuring out the different concentrations of acid, be careful not to spill it onto your hands or clothing. Method: To begin with, set up all the apparatus in a safe position. Then make up the different concentrations of acid. To do this, add a quantity of water to the acid. Water (cm 3) Acid (cm 3) Molarity Total (cm 3) 025125 5200. 825 10150.
625 15100. 425 2050. 225 Pour 25 cm 3 of each molarity of acid into a test tube. Then drop in a 2 cm strip of magnesium. As soon as the magnesium strip drops, start the stop clock. When the magnesium is no longer visible, stop the stop clock and record the time.
When the magnesium strip is dropped in a gas appears and it gives off a hissing noise. We can work out the name of this gas by solving a simple equation: Hydrogen Chloride + Magnesium = Magnesium Chloride + Hydrogen 2 HCL + Mg = MgCL 2 + H 2 Or collect this gas and test it with the 'POP test to identify it as Hydrogen. Do this with each of the different molarities and repeat this again at least two more times to ensure that an accurate result is achieved. BOILING TUBE ACID OF DIFFERENT MOLARITIES MAGNESIUM STRIP (2 CM) BOILING TUBE MAGNESIUM CHLORIDE (THE MAGNESIUM HAS REACTED WITH THE ACID AND HAS DISAPPEARED) I will record the results in a table under the following headings: MolarityVolume (cm 3) Size of Magnesium (cm) Time Taken (sec) Rate of Reaction 1 0. 8 0. 6 0.
4 0. 2 I will record the results in a graph under the following headings: T I M E (S E C) MOLARITY OF SOLUTION Prediction: I predict that the more concentrated the acid solution the faster the magnesium and hydrochloric acid will react. I think that this will happen because when there are more acid particles in the test tube the more chance there is of a successful collision: 1 2 3 - Acid Particle - Water Molecule - Magnesium Atoms 1. The particles in the liquid move around continually. Here an acid particle is about to collide with a magnesium atom. 2.
If the collision has enough energy, reaction takes place. Magnesium chloride and hydrogen are formed. 3. If the collision does not have enough energy, no reaction occurs. The acid particle bounces away again. Results: 1 st results; MolarityVolume (cm 3) Size of Magnesium (cm) Time Taken (sec) Rate of Reaction 125225 0.
825236 0. 6252131 0. 4252516 0. 22521137 2 nd results; MolarityVolume (cm 3) Size of Magnesium (cm) Time Taken (sec) Rate of Reaction 125224 0. 825240 0.
625263 0. 4252267 0. 2252 NO TIME 3 rd results; MolarityVolume (cm 3) Size of Magnesium (cm) Time Taken (sec) Rate of Reaction 125226 0. 825238 0. 625261 0. 4252232 0.
2252 NO TIME In some of the tests we had no time to complete them. I also made a table for my average results; MolarityVolume (cm 3) Size of Magnesium (cm) Time Taken (sec) Rate of Reaction 125225 0. 825238 0. 625285 0. 4252338 0. 22521137 I only recorded this result once because we had only enough time to test it once.
Interpretation and Evaluation: In this experiment I found out that many different factors including; Concentration, Temperature and Surface Area affect the rate of reaction. For the experiment I found out that the higher the concentration of the acid the quicker it takes to dissolve the magnesium. I know this because the more acid molecules that is in the beaker there is more chance of a successful collision to take place. Another factor that I learned is that the rate is constantly changing during the reaction because as time goes on there are fewer acid molecules.
There are fewer acid molecules because when the acid reacts the same particle cannot react again, so there are less to end with than there are to start with. As time goes on the number of acid particle decrease so there is less chance of a successful reaction to take place. Before I started the experiment I made up a prediction. I predicted that the more concentrated the acid solution the faster the magnesium and hydrochloric acid will react. I thought that this would happen because when there are more acid particles in the test tube the more chance there is of a successful collision. I was right in my prediction but I did not predict that the rate of reaction slows down as time goes on which did happen in my experiment..