Planning
I plan to investigate the effect of concentration of acid, in the reaction between hydrochloric acid and antacid tablets. The rate of a chemical reaction is a measure of how fast a reaction takes place. It is important to know that a rapid reaction is completed in a short period of time. In this experiment I will test different concentrations of hydrochloric acid reacting with antacid tablets.
My prediction
I predict that when the concentration of hydrochloric acid is increased, the rate that the reaction takes place will increase. I predict that if the concentration of hydrochloric acid is doubled then the rate of reaction will also double.
The concentration and the rate will be proportional to one another.
This prediction is supported by the collision theory. The collision theory states that when the concentration of an acid (in this case hydrochloric acid) increases then the rate of reaction also increases.
For a successful reaction to take place the ions of hydrochloric acid must collide into the atoms of the antacid tablet with sufficient energy.
This energy is called the activation energy.
The concentration of a given acid is a measure of how many hydrogen ions it has to react. A more concentrated acid will have more atoms to react, making the chance of a collision higher.
1 molar acid 4 molar acid
I would expect the reaction to slow down because as the ions are colliding they are also being used up. This means that as the reaction occurs, the concentration of the acid decreases (fewer particles to react). I would expect the graph to look like this:
Volume of Gas
Method
The apparatus I will need to use are:
- Hydrochloric acid (1-4 molar)
- Water (to dilute acid)
- 20ml syringe
- Antacid tablets
- Stopwatch
- Beaker with bung and delivery tube
- Bowl of water
- 50ml measuring cylinder
- Thermometer
- Clamp and clamp stand
I will need to set up the equipment as shown below:
I will have to fill the bowl and the 50ml measuring cylinder with water, making sure to fill the measuring cylinder to the very top.
I will then fill up the beaker with 15ml of hydrochloric acid with between 1 and 4 molars of concentration.
The delivery tube will be placed securely under the measuring cylinder and the cylinder will be clamped to hold it in position.
I will then place one antacid tablet into the acid and replace the bung.
I will start the stopwatch at 10 seconds because it is not possible for me to drop the antacid tablet into the acid, replace the bung and start the stopwatch all at the same time.
Instead of timing the reaction until the tablet has dissolved I will time it until it has produced 50cm³ of gas.
I will then repeat the experiment three times for each concentration and average out the results making sure to take away the extra ten seconds off the recorded stopwatch time.
To conduct this experiment safely I will have to wear goggles, gloves and a lab coat. I will wear gloves and goggles to protect my eyes and skin because the acid I will be using will be 4 molar hydrochloric acid, which is very caustic. If it were to come into contact with my eyes then it would burn through my retina making me blind, similarly if it were to come in contact with my skin then it could cause serious damage.
The results from this experiment will have to be fair. To make them as fair as possible I will have to do several things:-
- I will have to use a thermometer to check the temperature of the acid. The temperature could change my results dramatically. The hotter the acid, the faster the reaction. Heat changes the rate of collision because it makes the atoms vibrate more and gives them more energy, increasing the chance of a successful collision. From my preliminary results I found out that the average temperature of the acid was 19º, so I will try to keep the temperature of the acid as near to 19º as possible to make it a fair test.
- I will have to make sure the 50ml measuring cylinder is full to the very top with water on all the concentrations.
- I will have to make sure that 15ml of acid is used every time. More or less could change the result.
- I don’t need to be concerned about the mass of antacid tablets I put into the acid because they are all the same size and I only need one at a time.
- To make this a fair test I will need to redo each concentration of acid three times and then average out the results to give a more accurate result. If I were to only do it once then there is the possibility of a mistake but if done three times then the mistake will become clear and I could redo the experiment to get a new, more accurate result.
- To get a more accurate time I will start the stopwatch at 10 seconds. This is because I will not be able to start the stopwatch, drop the antacid tablet and place the bung on at the same time. Once I have taken the result I will take off the ten seconds that was added at the beginning.
- I will need to produce a 1.5 molar concentration of hydrochloric acid. To do this I will dilute 25ml of 3 molar acid with 25ml of water to produce 50ml of 1.5 molar. I will need 45ml of acid for my three experiments with the 1.5 molar acid. I will produce 50ml so that I will have some spare. The acid will be mixed as 50ml instead of mixing 15ml at a time. I will do this because the acid will then be exactly the same for each experiment and there is no room for error.
Results
I tried each experiment three times. I timed the reaction until 50ml of gas had been produced. I then averaged out the results.
Attempt 1 Attempt 2
Attempt 3 Average
Rate
Analysis
The results show that the higher the concentration, the lower the time taken for the reaction to occur. They also show that the higher the concentration, the higher the rate of reaction.
I have drawn two graphs. One of them shows time against concentration and the other shows rate against concentration. I have discovered that the rate and concentration are directly proportional to one another. I have discovered that as you double the concentration the rate of reaction also doubles. I proved this by drawing across from two molar until I met the line then drawing down from the line until I met the rate of reaction. I then did the same for four molar and discovered that the rate had doubled.
The graph looked like this:
4
2
Concentration
(Molar)
Rate
I conclude that when you increase the concentration the time taken decreases. When you increase the concentration the rate of reaction increases and the two are directly proportional to one another. I have drawn this conclusion from my evidence and my scientific knowledge of the collision theory.
The processed evidence shows that as the concentration increase the time taken decreases. This is consistent with the collision theory. The collision theory states that a reaction can only take place if particles collide with each other. The more particles there are to collide, the more chance of a successful collision.
My results support my prediction. I predicted that when the concentration of hydrochloric acid is increased, the rate that the reaction takes place will increase. I predicted that if the concentration of hydrochloric acid is doubled then the rate of reaction will also double and the concentration and the rate will be proportional to one another. The graphs support this because as 2 molar is doubled to 4 molar the rate of reaction doubles from 0.014 to 0.028. I then tried 1 molar doubled to 2 molar and the rate doubled again from 0.010 to 0.020. My results also show that when you increase the concentration the time taken decreases. I drew across from 4 molar and then down to time taken and the time was 152 seconds, I then drew across from 1 molar and the time taken was 37 seconds. This proves my prediction.
