- Catalyst: lowers the activation energy for the reaction. Many more collisions are ‘successful’, and the reaction is faster.
- Pressure: increase in pressure forces the particles closer together. This causes more collisions and increases the rate of reaction.
- Concentration: in solutions of higher concentrations particles are closer together. This means they have a greater chance of colliding.
The variable we are going to change is the concentration of acid. The factors we are going to control are the ½ cm pieces of Magnesium ribbon and 100ml of liquid.
To measure the 100ml of liquid accurately I am going to have 2 measuring cylinders, one for the 2m acid and one for the water to dilute the acid.
To measure the Magnesium I am going to use a ruler. The reason why I am not going to cut it ant smaller is because I don’t think you would be able to cut it to that accurate size.
The range of concentrations I am going to use is:
- 100ml of 2m acid
- 80ml of acid and 20ml of water
- 60ml of acid and 40ml of water
- 40ml of acid and 60ml of water
- 20ml of acid and 80ml of water
We are going to test each concentration three times to get an average.
The apparatus we are going to use are:
- Conical flask- to hold acid, water and magnesium
- Stop clock- to time the reaction
- Ruler- to measure magnesium
- Scissors- to cut magnesium
- Goggles- to protect our eyes
- Measuring cylinder- to measure acid and water
- 2m acid
- water
- magnesium
Safety:
While doing this experiment I will carry out these safety precautions.
Always wear safety goggles to protect eyes from the Hydrochloric Acid. Keep all the apparatus away from the edge of the desk to prevent breakages.
Aim:
The aim of this investigation is to find out the effect of concentration of acid, in the reaction between dilute Hydrochloric acid and Magnesium ribbon.
Prediction:
I predict that as the concentration of Hydrochloric acid decreases, the time taken for the Magnesium to dissolve increases.
Method:
Firstly I measured out the amount of 2m Hydrochloric acid using the measuring cylinder. I used the measuring cylinder to pour the acid into the conical flask. Then I cut my magnesium into ½ cm pieces then added it to the acid, and started the stop clock at the same time. When the magnesium ribbon had stopped fizzing, I stopped the clock and recorded the time.
I used the same method only when I had done three readings of the same concentration, I then replaced 20% of acid with water each time.
Results:
Analysis:
The graph supports my original prediction of: as the concentration of hydrochloric acid decreases, the time taken for the magnesium to dissolve increases.
Looking at the set of results, you can clearly see that they follow the expected pattern. The pattern shows that when the concentration of acid increases this makes the rate decreases. This is because if you increase the concentration of the acid you are adding more particles in to the reaction which will produce a faster reaction because there are more successful collisions.
When the concentration of acid is increased the rate of reaction is faster.
When the concentration of acid is decreased the rate of reaction is slower.
Conclusion:
From looking at my graph I have observed that it has backed up my prediction. As it shows on the graph, when the concentration of hydrochloric acid decreases, the time taken for the magnesium ribbon to disappear increases.
This is because in a higher concentrated solution, the particles are closer together, which means they collide more often, making a faster rate of reaction.
I conclude that the higher the concentration the faster the reaction rate. This is because the particles collide more. I can tell this from my graph because when there was 100mls of 2m acid the reaction was very fast.
When I increased the amount of water to the acid the reaction rate of magnesium ribbon dissolving in hydrochloric acid got slower.
Evaluation:
My experiment went well as it backs up my prediction. The higher concentration the faster rate of reaction. It was a fair test and there is only one anomalous result that I could find.
My anomalous result was with 60mls acid and 40mls water. The result for this was 69 seconds but from what the line of best fit shows, it should have been around 56 seconds
I could improve the investigation by taking more care in measuring out the different amounts of liquid more accurately. I also think that we should have done all the experiments on the same day as the temperature in the room would have been the same.
The factors that could have caused my anomalous result are:
- condition of magnesium
- temperature in the room of the day of the practical
- accuracy of measuring
I could have improved some of these by checking that all the magnesium was all the same size before putting it into the hydrochloric acid and that I use the same concentrated acid in every repeat i.e. 2 molar.
In this investigation I found out that the higher the concentration, the faster rate of reaction.
I think my investigation was a fair test and that I got a good accurate set of results.
Catrina Kottritsch
