Aim
I am going to investigate the effect the concentration of acid between hydrochloric acid (HCL) and magnesium ribbon. In my investigation I am going to test different concentrations of acid reacting with magnesium ribbon.
Prediction
I predict that the more concentrated the acid gets the faster the rate of reaction will be. The more concentrated the acid is, means that it will only take a short amount of time for the magnesium ribbon to disappear.
“Richard Parsons materials and their properties”
Reason
The collision theory states that the higher the concentration of the hydrochloric acid the faster the rate of reaction. This is because there are more particles in the reactant meaning that there are going to be more collisions between particles. The more concentrated the acid the shorter period of time it will take for the magnesium ribbon to disappear. For any reactions to take place a fixed amount of energy needs to be reached before the reaction takes place. This energy is called Activation Energy (Ea) “Bob McDuell Chemistry” collisions need to be fast enough and they need to be going in the right direction for reactions to take place.
When magnesium ribbon and Hydrochloric acid react the products will be Magnesium chloride and Hydrogen gas.
The formula for this is
Magnesium + Hydrochloric Acid Magnesium Chloride + Hydrogen
Mg(s) + 2HCL(aq) MgCl2(aq) + H2 (g)
If the collision between magnesium ribbon and the hydrochloric acid has enough energy, a reaction will take place. Therefore the higher the concentration of the reactants, the more collisions will occur. If the particles have enough energy Magnesium Chloride and hydrogen gas will be formed. But if the reactant doesn’t have enough Activation Energy a reaction won’t take place. Activation Energy is the energy that needs to be present for the bonds of the reactant to be broken and for new bonds to be produced in the product. Once there is enough Activation Energy, the reaction sufficient energy to start.
As the concentration of the acid decreases so does the rate of reaction, as there are less particles to collide into one another.
“ Bob McDuell 1994 pg 93”
This is an “exothermic reaction” this means that heat energy is given out.
The energy of collision must be greater then the bond between the atoms.
Variables
In my experiment I am going to keep the following things constant:
- Amount of magnesium ribbon used
- Amount of hydrogen gas collected
- Amount of Acid used
I am going to change the following things in my experiment:
I am going to repeat this experiment four times so that I can obtain accurate results. I am going to use five different concentrations of acid in my experiment.
Fair test
To make this experiment a fair test I will:
- Amount of magnesium ribbon used
- Collect the same amount of gas
- Use the same volume of acid all the time
Apparatus/ diagram
For this experiment you will need:
- Magnesium ribbon 0.15 grams each time
- Hydrochloric acid up to 2 moles
- Water (to dilute acid)
- Pipette
-
Measuring cylinder – 35CM3
- Gas syringe
- Stop watch
- Clamp
- Conical flask
- Safety goggles
Method
- Collect apparatus
- Set up as shown above
- Collect magnesium ribbon 0.15g
-
Measure out 25 cm3 of HCL acid using a measuring cylinder (change concentration as appropriate)
The concentrations that I am going to use are:
- 1.66 molar
- 1.34 molar
- 1 molar
- 0.66 molar (you have to change the concentration of the acid by diluting the acid with water)
- Make sure that you are wearing safety goggles
- Place acid into flask
- Place magnesium ribbon in to flask
- Quickly place bung onto flask
- Check that the bung is securely on, and there are no gaps
- Start timer quickly
-
When 50cm3 of gas has been collected stop timer (always make sure that you have 50cm3 of gas, other wise it is not a fair test)
- Record results into results table
- Repeat the whole experiment again using different concentrations of acid
- Form results get an average and then draw your graph
- After you have collected all of your results work out the Rate of Reaction using the formula:
Rate of Reaction = Quantity of product/ reactant
Time taken
Conclusion
This experiment proved my prediction correct.
From this experiment I found that the higher the concentration of the acid used the higher the rate of reaction. This is because there are more particles of hydrochloric acid to react with the magnesium in a higher concentrated solution. It is the hydrochloric acid particles that need to have the most Activation Energy (Ea) as they have to bond with the magnesium to produce magnesium chloride. In order for a reaction to take place collisions need to occur, these collisions need to have enough energy for bond to break to form new substances.
=HCL acid
= Magnesium strip
The graph of results supports my prediction of: the more concentrated the acid the higher the rate of reaction. In a higher concentration there are more acid particles to react with the magnesium ribbon and therefore it is reacted with faster. When the concentration of the acid was 2 moles it took an average of 6.25 seconds to collect 50 cm3 of gas, and when the concentration of the acid was 1 mole it took 58.33 seconds to collect the same amount of gas.
Looking at the set of results obtained, you can clearly see that there is an anomalous result. This may be due to a number of reasons. One of the reasons may be due to human error. It also could be due to faulty equipment. If you increase the concentration of the acid you are adding more particles into the reaction, which will. Consequent in a faster reaction because there will be more collisions between the particles which is what increases the reaction rate.
As you go down the table of results you can see the less concentrated the acid gets the more time it takes to produce 50cm3 of hydrogen gas. You can also see that the less concentrated the acid gets the lower the rate of reaction. E.g. when the concentration of the acid was 1 mole the rate of reaction was 1.14…. the faster the particles react the harder it is to get an accurate rate of reaction as accuracy is not that good.
This set of results is fairly accurate in comparison to the equipment we had available. I think that the results are not accurate, as there was a time gap between us putting the magnesium into the flask of acid and putting the bung onto the flask. This meant that some gas was lost.
To improve this experiment I would repeat it again. But I think that 4 times was enough to get an accurate average. From the scientific information I have read about when the concentration doubles the rate of reaction should also double, this is because the ions are closer together in a concentrated solution. My graph doesn’t prove this theory correct, but there were fairly accurate compared to the equipment I had available. I still some anomalous results, this may be due to change in environment or inaccurate readings.
Evaluation
I think that my method was correct, as my experiments did run smoothly. If I could do the experiment again I would do all the experiments in one day, so that there wouldn’t be a change in environment. The accuracy of my experiment was good in comparison to the equipment we had available. One thing that should be improved on was the time period it took for us to place the bung on the flask, this would have effected the time taken to produce 50cm3 of hydrogen gas. Another reason for these anomalous results is that the concentration of the acid could have been wrong. Another possible reason is that when the flask was washed it may have been washed with too hot or too cold water, which would have changed one of the variables I was keeping the same in my experiment. As you can see from my results table my results were constant throughout the repeats of the experiment. If I could do the experiment again I would have repeated it again to get a more accurate average. Overall I think that my experiment went well, and that I obtained accurate results.
Diagram
