How the Concentration of Acid in a Solution affects the Rate of Reaction
Investigation into: How the Concentration of Hydrochloric Acid in a Solution affects the Rate of Reaction
Aim:
This experiment was to observe how the concentration affects the rate of reaction between chemicals. The two chemicals used in our experiment were Sodium Thiosulphate and Hydrochloric Acid.
Introduction:
The rate of reaction is basically the speed of how fast the reaction occurs between two reactants. You measure this speed in seconds, and have to set an achieving limit, which is a standard point of the reaction where a change is noticed and that is where the time must be recorded. A reaction is the simply the collision of the particles in two different substances (reactants).
This essay is about writing how we observed the chemical reaction we carried out. Now here's the bit where the story gets interesting...
My Prediction:
My prediction is that: as long as the chemicals react in the same amount as was set, the speed of the reaction will be faster as the concentration (molarity) of the Hydrochloric Acid is increased. I predicted this because generally, when something has a higher concentration, it reacts quicker than when it has a lower concentration. This theory is ~
"Increasing the concentration increases the rate of reaction". This is because when there are more particles present, there is more collision between the particles; this increases the rate of reaction. (Theory explained thoroughly in conclusion).
Preliminary Test:
Before conducting the experiment I had first to determine the ratio of Hydrochloric Acid and Sodium Thiosulphate that give the best range of results. We observed how long it took 5cm³ of Hydrochloric Acid (in different concentrations) to react with 10cm³ of Sodium Thiosulphate. This was very slow and it was still possible to see the "X". I repeated this 3 more times increasing the volume of Sodium Thiosulphate but keeping the volume of the Acid the same. By doing this I decided on my final experiment to use 30cm³.
Method we used:
We set the stopwatch as soon as both chemicals were in contact and placed a small piece of card (with the letter "X" drawn across it) underneath the conical flask that the reaction was taking place in. As soon as the "X" on the card was no longer clearly visible, we stopped the stopwatch and noted the time. To be very accurate, we did this experiment with every different concentration 5 times and put the results in a table.
Apparatus:
* Chemicals (Sodium Thiosulphate & Hydrochloric Acid)
* Beaker
* ...
This is a preview of the whole essay
Method we used:
We set the stopwatch as soon as both chemicals were in contact and placed a small piece of card (with the letter "X" drawn across it) underneath the conical flask that the reaction was taking place in. As soon as the "X" on the card was no longer clearly visible, we stopped the stopwatch and noted the time. To be very accurate, we did this experiment with every different concentration 5 times and put the results in a table.
Apparatus:
* Chemicals (Sodium Thiosulphate & Hydrochloric Acid)
* Beaker
* Pipette ×2
* Measuring cylinder ×2
* Stopwatch
* Conical flask
* Card with "X" drawn on it
Method:
We had two measuring cylinders which we used for the two chemicals named above. Each time we changed the concentration of the Hydrochloric Acid, we washed out the measuring cylinder and the pipette we used to put the Hydrochloric Acid into the measuring cylinder.
We were told to pour 30cm³ of Sodium Thiosulphate into a measuring cylinder, and 5cm³ of different concentrations of Hydrochloric Acid into the other measuring cylinder; and to record the results. After each time we pour the correct amount of the chemical into each measuring cylinder, we poured both amounts together into a beaker. There was a card "X" drawn on it with a blue marker pen under the beaker and the experiment was to observe how long it took until we could not see the "X" on the card.
The concentrations of the Hydrochloric Acid were 1M, 1.5M, 2M, 2.5M and 3M. We did the experiment with each concentration 5 times to be totally accurate.
Then, carefully, we put away the chemicals and we washed the apparatus that needed to be washed, and cleared up. This is an important part of an experiment as the "health and safety" policy is essential. Without carefully putting away the apparatus, the irritant chemicals and glass tubes could be harmful, and may be fatal.
Results Table:
Concentration Of Hydrochloric Acid
(Mole)
Time taken in reaction.
stTime
(mins)
Time taken in reaction.
2ndTime
(mins)
Time taken in reaction.
3rdTime
(mins)
Time taken in reaction.
4thTime
(mins)
Time taken in reaction.
5thTime
(mins)
Average Time
(mins)
M
3.24
.14
.18
.14
2.48
:08:72
.5M
.08
.02
.05
.13
.13
:00:82
2M
.05
.07
.10
.03
.10
:00:70
2.5M
.06
.07
.03
.06
.08
:00:60
3M
.00
.05
.00
.03
.02
:00:20
(Graph for table of results attached on next page)
Conclusion:
There are a few areas I want to cover in the conclusion about this experiment.
The patterns I noticed occurring as the reaction continued were related to the variable reactant. The pattern was that when we added Acid with more concentration to the Sodium Thiosulphate, the reaction was faster. This means that the slowest reaction was when Sodium Thiosulphate reacts with Hydrochloric Acid with a molarity of 1M; and the fastest reaction was when Sodium Thiosulphate reacts with Hydrochloric Acid with a molarity of 3M.
The reaction theory law is that: ~
..."Increasing the concentration increases the rate of reaction"...
There is a straightforward explanation for reactions called collision theory. This theory explains and describes how the reactants collide in a reaction.
The tiny particles that make up a substance might be atoms or molecules. Molecules are made of atoms that are joined together. A chemical reaction happens when the reactant particles bang into each other. The clash of the particles banging into each other is called collision. If the particles collide hard enough, the reaction takes place. The amount of energy enough to cause a reaction is called the activation energy. The more collision there is, the faster the reaction is.
This means that the reaction depends on the amount collision between the two reactants. If the concentration of a reactant is stronger, there are more particles in the same volume to react with the particles in the other substance, and vice versa.
So the actual particles are doing all the work, while the other reactants' particles try the same thing, to react back. This causes a fight, but there is no winner or loser, just a product (the result of the reaction). The product would be most likely a gas, a liquid, or less likely a solid.
The gradient of my graph was positive, which matched my prediction. This was pleasant as I saw my theory being proves true.
My prediction was also correct and the experiment showed the patterns I expect to see.
Evaluation:
When this experiment was being done, we did not have a vast quantity of the apparatus, so every reaction took place in the same conical flask, which also had been washed just before they were used and were not dry.
So to make this better I would use a different conical flask for every reaction, and they would be clean and dry ones. This means that there should be 25 clean (sterilised), dry conical flasks for the whole experiment to be carried out efficiently.
The pipette that was used for the hydrochloric acid was also replaced with a clean, dry pipette. So there was no mix of molarity. That was a sensible idea to gain reliable results.
The thing that concerned me was the results ~
We were unsure at what point to note the time, so the first set of outcomes were slightly dodgy. This confusion was first revealed when the cross underneath the conical flask failed to totally fade. So then we randomly stopped the time when we got fed up of waiting, and after that, we stopped the time when the some parts of the cross were not entirely visible. This made the outcomes similar to the pattern, and the "increasing concentration" theory made proved itself true in the practical.
We could have also used computer sensors for timing which would have given us more accurate results. Also, repeating this experiment as many times as possible would lead to better results and a stronger conclusion.
There are many different experiments that we could carry to investigate the rate of reaction. Some of these are:
* Varying the temperature
* Applying pressure
* Increasing surface area of the particles
* Using a catalyst
My overall comment for this experiment is that:
Despite using accurate but imperfect equipment, my practical was a complete success and matched the theory that "the rate of reaction is directly proportional to the concentration of the reactants.
~ Syed Jafri ~ 11 East ~ Chemistry Coursework ~
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