The variables that I will be investigating are:
- Concentration
- Surface area
- Temperature
A reaction will only occur if the colliding particles possess more than a certain minimum amount of energy. This minimum energy for a reaction to occur is known as the activation energy (EA) the activation energy also enables chemical bonds to stretch and break the rearrangements of the atom, ions, and electrons to occur as the reaction proceeds.
Hypothesis
It can be predicted, according to scientific evidence that as the temperature rises, the calcium carbonate will gain energy and cause the particles in calcium carbonate to collide faster and more often ( collision theory ) resulting in a quicker rate of reaction.
Moving on to the second variable it can be predicted that increasing the concentration of hydrochloric acid will result in more gas/cm to be produced. This will reflect the fact that the greater the concentration of reactant, the greater the chance of a successful collision, i.e. the more particles that there are, the more they will collide per second resulting in an increase in the rate of reaction.
Moving on to the third variable, it can be predicted that increasing the surface area of the calcium carbonate would also result in more collision per second, and the faster the reaction is going to be. You can increase the surface area of calcium carbonate by breaking it up into smaller pieces. A powder has the largest surface area and will have the fastest reaction rate.
Fair Test
- In order to ensure a fair test with reliable results, only one variable will be changed per experiment. E.g. experiment A- concentration of acid will be changed. However temperature and surface area will be kept constant. If we choose to change the concentration of acid and surface area of calcium carbonate, you will find that the highest concentration of acid and the largest surface area will result in a faster rate of reaction than if you were to change just one variable. This also applies to temperature and surface area. The results will all be directly proportional.
- The temperature of the acid- water mixture needs to be accurate to get the correct rates of reacting calcium carbonate.
- The size of the calcium chips needs to be kept at 5g as changing the surface area will result in varying factors. Large surface area will result in wrong results because it has a larger area to react with therefore the time it would have taken would be more than it should be.
- The hydrochloric acid cannot be used again otherwise the acid will be less strong to act on the calcium carbonate.
Concentration
- Clamp
- Measuring cylinder
- Conical flask
- Goggles
- Weighing boat
- Scales
- Stand
- Stop watch
- Pipette
- Boss
- Beaker
- Side Arm
- Delivery tube
- Gas syringe
- Strainer
- Kettle
- Bung
- Bung
- Thermometer
Concentration
- 5g of calcium carbonate
-
HCL/ cm3 2M (varying amounts of H2O
-
Acid conc. / moldm-3.
Surface Area
- 5g of calcium carbonate
-
HCL/cm3 2M (15cm3 )
-
H2O (10 cm3 )
Temperature
- 5g of calcium carbonate
-
HCL/ cm3 2M (15 cm3 )
-
H2O (10 cm3 )
- Heated water at 30, 45 and 60 degrees Celsius.
Method
- Since I will be working with acids, to ensure optimum safety I will wear safety goggles and a lap coat while conducting my experiment.
- To make sure I can rely on my results I will repeat the experiment two or three times if necessary, because there is a chance of inaccurate results.
- I learnt from the trial experiment when reacting Mg with HCL, that it is quite hard to start a stopwatch, pour and stick a bung into the conical flak all at the same time, so I will get someone to assist me while doing so.
Concentration
- Measure 5g of calcium carbonate with each of the different concentrations (i.e. medium, small)
-
Pour the 5g of calcium carbonate adding HCL acid (varying from 25cm3- 5 cm3 )
-
Add H2O depending on the vol. of HCL acid (i.e. 20 cm3 HCL being 5 cm3 of H2O)
-
When you have added the calcium carbonate, hydrochloric acid and water into the conical flask close the bung and record the speed it will take to reach 40 cm3 of gas (CO2) for each volume of HCL and H2O reading.
- Rinse conical flask.
Surface Area
- Measure 5g of calcium carbonate with each size varying.
-
Add 15 cm3 of H2O and 10 cm3 of HCL acid.
- Add calcium carbonate, hydrochloric acid and water into conical flask and close the bung and record the volume of gas collected every 10 seconds for 90 seconds.
- Repeat each size
- Thoroughly rinse the conical flask out.
Temperature
- Measure 5g of calcium carbonate with each size varying.
-
Use same acid-water mixture of 15 cm3 of HCL and 10 cm3 of H2O respectively for all the temperatures to be investigated.
- Place mixture unto a beaker and place a thermometer to record your acquired temperature.
-
Add beaker solution into conical flask and record the time taken to collect 40 cm3 of gas.
Reaction Equation
CaCo3(s) + 2Hcl (aq) = CaCl2 (aq) + H2O (i) + CO2 (g)
Obtaining the Evidence
Whilst carrying out the experiment I carried out each test twice and recorded the mean to get a more accurate and precise result.
Table of Results
Investigating Factors Affecting Concentration
Large Calcium Carbonate
Medium Calcium Carbonate
Small calcium carbonate
Powder Calcium Carbonate
Investigating Factors Affecting Surface Area
Large Size CaCO3
Medium CaCO3
Small Size CaCO3
Investigating Factors Affecting Temperature
Large size CaCO3
Medium Size CaCO3
Small Size CaCO3
Conclusion
In drawing together a conclusion for the investigation of rates of reaction, we can see from the table of results and line graphs that as the temperature increases in the rate of reaction, the energy increases resulting in a faster rate if reaction. I.E. when the temperature for the large Calcium Carbonate is at 30 degrees the time taken to collect 40 cm3 of gas is 32 seconds. But when the temperature is increased to 60 degrees the time decreases to 16 seconds. This evidence can be explained by scientific theory. At higher temperature particles are moving around faster. They therefore collide more frequently and with more energy. This means the reaction rate increases when the frequency or energy of collision between particles increases.
In drawing together a conclusion for the surface area, we can also see that from the table of results and line graphs that when we increase the surface area of a large marble chip, we increase collision; I.E for the large marble chip, the Calcium Carbonate took 10 seconds to measure 12 vol. of CO2. Unlike the powdered size marble chip which took 10 seconds to measure 35 vol. of CO2. I can gather this theory and join it with my scientific theory. The reaction between the Calcium Carbonate and acid is much faster when the marble chip is powder because there are more atoms exposed and which are highly more likely to dissolve unlike the large marble chip. So there is a greater chance of a successful collision.
In drawing a conclusion for the concentration rate we can also see that from the graphs and table of results that when the reaction between Calcium Carbonate and Hydrochloric acid first starts, the reaction is fast. As we decrease the amount of Hydrochloric acid, the reaction starts to slow. We can see this because the gradient of the curves in my line graph are steep at the beginning of the reaction. I.E at 2 moldm-3 the time taken to collect 40 cm3 of gas for the medium Calcium Carbonate is 20 seconds. At 0.4 moldm-3 the time taken to collect 40 cm3 of gas increases to 180 seconds. The cause of this result and curve is at the start of the reaction there is the most acid molecules that are colliding with the marble. But as the acid molecules decreases the time taken to measure 40 cm3 of gas increases.
I can join my table of results and line graphs to my scientific theory. The products of a reaction are formed as a result of the collision between reactant particles. There are more particles in a more concentrated solution and collision occurs more often. The more often they collide the more chance they have of reacting. This means that the rate of a chemical reaction will increase if the concentration/surface area/temperature is increased.
Evaluation
My experiment showed a couple of anomalies points. For my 2nd experiment, investigating the factors affecting surface area, the time taken for the large Calcium Carbonate to measure 40 cm3 of gas took 40 seconds which was longer than expected. For my 3rd experiment, investigating the factors affecting temperature the time taken for the large Calcium Carbonate to measure 40 cm3 of gas at 30 degrees took 32 seconds which was shorter than expected.
The possible causes of these anomalies results could be due to the fact that we cannot be sure whether the Calcium Carbonate was pure enough, because their could have been rocks or small salts in the Calcium Carbonate which increases the amount of time. The kettles may have had lime scale present which means the rate of reaction will slow down, due to the lime scale interference with the process of reaction.
Generally the method gave evidence that can be deemed as reliable due to the lack of anomalies. These anomalies can be due to the above causes. A fair test was strictly kept in all experiments. The evidence is thus enough to draw a conclusion on the rates of reaction. Enough to say that ‘the rate of reaction increases when temperature, concentration and surface area increases.
However at the same time, more repetitions of the experiment would make the results even more reliable. Not only repetitions at one point in time but repetitions over a number of weeks to make sure those factors such as atmospheric pressure, room temperature and drafts do not interfere with the results. Repeating the experiment over time will take this into account. After having done the experiment a graph of means can be worked out bringing a pod of evidence together to draw a tight conclusion.