The preliminary showed that the experiment worked. I decided to use 5 different type of concentration of hydrochloric acid and they were all going to be 50 ml and I am going to use 0.5 grams of marble chip in each concentration. I am going to use this amounts because
Collision theory
Collision theory states that reaction can only happen when reactant particles collide with each other, but most collision of the particles are not successful in forming the product even though the high rate of collisions between the particles. This is because that the particles have a wide range of kinetic energy but only small fraction of particles has enough kinetic energy to break down the bonds and bring about chemical changes. The particles of the reactant are required to have activation energy for the particles to collide and react. Activation energy means that the reactants must have a minimum kinetic energy. If the colliding particles have less than the minimum energy, then they just bounce off each other and no reaction occurs. The minority high kinetic energy collisions between particles which do produce a chemical change are called ‘fruitful collisions’. This means that the particles of the reactant collide with enough kinetic energy to break the original bonds and form new bonds in the product particles.
Temperature affecting the rate of reaction
The rate of the reaction will slow down or speed up depending on what temperature. In a low or cold temperature it is hard for the particles to break down and the rate of the reaction therefore will be slow. In a high or a hot temperature the rate of reaction will speed up because the particles gain kinetic energy and move faster (see Diag.1). The increased speed increases the chance of the particles of the reactant collide each other. Also the faster the particles are travelling, the greater is the proportion of them which will have the required activation energy for the reaction to occur. The colliding particles of the reactant must have a minimum kinetic energy called the activation energy. Endothermic and exothermic are not the factors that change the rate of reaction, is the activation energy is an important factor in terms of temperature and reaction speed.
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Low temperature High temperature
Concentration affecting the rate of reaction
The concentration of acid hugely affects the rate of reaction. Increasing the concentration of a substance in a solution means that there will be more particles per dm3 of that substance Also increasing the concentration, increases the probability of a collision between reactants particles because there are more of them in the same volume and so increases the chance of a fruitful collision forming the products.
E.g. increasing the concentration of acid molecules increases the frequency or chance at which they hit the surface of marble chips to dissolve them. (Showed in Diag. 2)
Diag.2
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Slower Faster
High concentration acid has more moles of acid than water. In a low concentration acid, it has more moles of water than acid. High concentrated acids are stronger than low concentrated acid which means that high concentrated acid speeds up the rate of reaction this is because the acid breaks down the particles faster
Surface Area affecting the rate of reaction
A solid in a reaction can only react if the particles of an acid collide with the surface of the solid. The bigger the surface area of the solid surface, the more solids can collide with it per second and faster the reaction rate is. The rate increases because smaller pieces of the same mass of solid have a greater surface area compared to larger pieces of solid. (Showed in Diag.4) The surface area of a solid can be increased by breaking it up into smaller pieces.
Diag.4
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Small surface area large surface area
Catalyst affecting the rate of reaction
A catalyst is used for changing the rate of reaction. It is often used to make the reaction go faster. The catalyst does not take part in the reaction as a reactant. It is not changed by the reaction and is not used up during the reaction. It’s in the same form when the reaction is complete. Catalyst increases the rate of a reaction by helping break chemical bonds in reactants molecules and provide a ‘different pathway’ for the reaction. A catalyst is often used as a powder so it has a bigger surface area per gram.
Catalyst works by providing a suitable surface for the reaction to occur. The reacting particle gather on the catalyst surface and collide more frequently with each other and more of the collision result in a reaction between particles because the catalyst can lower the activation energy for the reaction.
Pressure affecting the rate of reaction
Increasing the pressure where the reactant is a gas is similar to increasing the concentration of a reactant in a solution. The particles are closer in high pressure which makes the particles collide more frequently and have a fruitful collision. This makes the rate of reaction increase.
Fair Test
I was careful to make this a fair test by keeping all my variables (except the concentration of the acid) constant. I used the same mass number of marble chips that I put in different concentrations of acid.
To make it a fair test I will have to keep the room temperature the same for every experiment. If the room temperature is high the rate of reaction will be fast, this is because the particles will have more energy to break down, the particles which will also speed up the reaction. If the temperature is cool or cold than the rate will be slow for the reaction.
I have to keep the concentration of hydrochloric acid the same for every type of experiment because in a high concentration acid the rate will be faster than the weak concentration acid. I have to use the same moles of acid when I am testing a particular concentration. The particles will easily be broken down in a high concentration acid than in a low concentration acid.
The pressure in the container is also an important factor.
If the pressure is high in the container the rate will be fast because the particles of the marble chip will collide with the particle of hydrochloric harder and hit the side of the container than in a low pressure container. That means I have to keep pressure constant
The surface area of the marble chip also affects the rate of the reaction. If the surface area is big or large the rate will be faster than a small surface area marble chip reaction. This is because in a large surface area marble chip the chips will hit hard which will easily break down the particles. To prevent this I weighed the marble chips.
The catalyst can also be used to fasten up the rate of reaction. There are two types of catalysts, Positive and Negative catalysts. Positive catalysts fasten up the reaction and negative catalysts slow down the rate of reaction. Catalyst doesn’t react with the experiment just speeds it up.
Obtaining Evidence
I am going to test five different moles of hydrochloric acid and I am going to repeat the experiment two times to make sure I got accurate results.
I set up the apparatus as shown in the diagram above. I took precautions to wear goggles because I was handling acid.
To keep this experiment a fair test, I had to keep all my variables apart from the concentration of acid the same.
Calculating the mole
Here is how I made the moles of my acid.
If 25ml of hydrochloric acid is 4 moles I added 25 ml of water so it is now 2 moles.
I made sure that I used the same mass of marble chips each time and the same volume of hydrochloric acid too. I used different molars of concentrated acid to test the rate of reaction in each concentration.
I am going to fill a plastic box with water, then I will fill up the measuring cylinder and put it upside down in the plastic box with water. I am going to keep my hand on top of the measuring cylinder while I am doing this because I don’t want the water to get out. I’ll set up my apparatus and make the five different concentration of acid. Later on I put the end of the delivery tube in the measuring cylinder without removing it from the plastic box. This is for carbon dioxide where I will measure how much it was produced by reading the measuring cylinder. Then I poured my concentration of acid in the conical flask and put 1 gram of marble chip which I weighed it by using the electric balance and then, I quickly put the cork on top of it and started the stopwatch. The cork has a tube which I put the other end of the deliver tube on top of it to get the carbon dioxide in the measuring cylinder. I recorded how many carbon dioxide was produced every 20 seconds until 2 minutes and 20 seconds
Method
- Fill the box with water
- Fill a 200ml3 measuring cylinder with water
- Put the measuring cylinder upside down in the box with water. Put your hand on the top of the cylinder to make sure no water goes out.
- Add acid in the conical flask
- Put 1 mole of marble chip in the conical flask and quickly put the delivery tube on top of it. ( weigh 1 mole using the electric balance)
- Start the stopwatch.
- Record the results every 20 seconds
Results
The red highlighted results are the anomalies.
I repeated the experiment two times for testing if the results were accurate.
Repeat 1
Repeat 2
Averages (rounded to 1 decimal place)
Analysing Evidence
I used the results obtained to plot a graph of time taken against concentration of acid. I used the average results to plot the graph.
The graph shows that high concentrated acid produce more carbon dioxide then less concentrated acid. It also shows that high concentrated acid produce more carbon dioxide every 20 seconds. This is due to the collision theory and the kinetic energy which is required for the particles to collide. As the time interval increases, more carbon dioxide is released by the marble chips, this happens because the acid particles starts to collide more with marble chips particles and so more carbon dioxide is released. This explains my hypothesis and proves my prediction was correct.
The graph shows a straight line for each concentration of acid which goes steeper as the time increases which means the rate of reaction increases.
This is the formula for calculation the rate of reaction.
Rate of Reaction= Carbon Dioxide/ Time Taken to release carbon dioxide.
This sign / means divide.
Now I am going to calculate the rate of reaction for each concentration by using the formula which is shown above. I rounded my results to 2 decimal place.
1.5 mole : 497.5/ 140= 3.55 cm3/ sec
2.0 mole : 588.7/ 140= 4.21 cm3/ sec
2.5 mole : 755.0/ 140= 5.40 cm3/ sec
3.0 mole : 776.9/ 140= 5.55 cm3/ sec
3.5 mole : 1150 / 140= 8.21 cm3/ sec
My formula shows that 3.5 molar acid had the fastest rate of reaction compared to other molar acid. The result also shows that high concentrated acid are faster than low concentration acid.
From my graph and the result I worked out form my formula, I came to a conclusion that as the time increases more carbon dioxide is released and high concentration of hydrochloric acid has a faster rate of reaction than low concentrated acid because they produce more carbon dioxide than low concentrated acid. The evidence that proves that my prediction is correct is shown above. This is because of the collision theory that I explained it in the planning section. High concentrated acid has more particles than low concentrated acid which increases the frequency of the particles of the reactants to collide each other. More collisions mean faster rate of reaction. This proves my prediction and hypothesis and it shows that collision theory works with this experiment.
Evaluation
The experiment went quite well. There were some anomalous results in my experiment which I carried out repeats to get accurate results. The reason for my anomalous results would be because I might have misread the readings or used a different concentration of acid. Another reason for my anomalous result is that I marble chips with different surface area. This had a huge effect on my investigation because it is an important factor in my experiment and the particles of the marble chips collide with acid more if the marble has a large surface area. I’ve could’ve also used a gas syringe to collect carbon dioxide to avoid anomalous results.
Next time if I carry out my experiment again, I’ll use powder marble chips which will have the same surface area and I’ll take more accurate measures by using the gas syringe and make sure that I don’t mix up the concentration of the acid.
Mohammad Yousuf Chemistry Coursework
