Mass of marble chips- The mass of the marble chips is a way of measuring the quantity of chips being used.
Temperature - Is a measure of the motion of particles, increasing the temperature will cause the particles to move faster. When particles move faster, more frequent collisions will occur and the collisions are more violent This should increase the reaction rate. This will result in the particles colliding more frequently and increasing the speed of the reaction. Also when they have more energy there will be more chance of the collisions being successful because the activation energy will be attainable.
Hypothesis:
I predict that the higher the concentration of HCl acid, the higher the reaction rate will be, this is because in a higher concentration there will more hydrochloric acid molecules per set volume. This means that there will be a higher chance of the calcium carbonate molecules colliding with the hydrochloric acid and reacting. This should in theory increase the rate of reaction as the concentration is increased.
The increase in the concentration should be directly proportional to the increase of the reaction rate at a given time. This is because by doubling the number of hydrochloric acid molecules present the chance of a collision should be doubled, as there is now twice the possibility of a collision-taking place initially. This can be thought of as like people in a refined space, if there are twice the number of people there will be twice the chance of people colliding. This situation may change over time, however, depending on the situation.
The Collision Theory
From the kinetic theory of gases, the collision theory of bimolecular reactions in a gas phase was developed. In a reaction between two gaseous substances A&B a molecule of A must collide with B for the reaction to proceed but in a concentrated solution there will be a higher percent of reactants which will have no more energy. Not all collisions cause a reaction, only the ones which reach the activation energy of the reaction. This is why I predict that the rate of reaction will increase as the concentration of a solution increases.
Safety
To make sure we are safe in the laboratory, here are some of the things we will do in more detail.
·Wear safety goggles because we are dealing with an acid
·Tuck stools in to make sure no-one falls in the lab
·Put all bags under the table to avoid accidents
·Never run in the lab
·Always stand up when carrying out experiments so we can move away if we are in any danger.
The following apparatus will be needed for the experiment:
. 250ml Conical flask- this will be used for the reaction to take place because it is large enough to hold the reaction
. Measuring cylinders (100ml)- because these are different size it will enable us to measure higher volumes
. Big Bowl- we will use this to put the cylinder of water upside down in so water does not spill
. Delivery tube- this will be used for the gas to travel down and will be useful because we will not have to hold the conical flask.
. Stopclock- this is needed to measure the time it takes to collect a specific amount of CO2.
I will also need:
. Thistle funnel
. Beehive Shelf
. Top-pan balance
. Safety Goggles
. Medium Size Marble Chips
. 2 molar HCl
. Distilled Water
. Spatula
. Cotton Wool
Underneath is a diagram of how the experiment was set-up.
FAIR TEST:
To make this experiment a fair test we will keep all values we are not investigating the same. We will use the same volume of HCL and the same amount of CaCO3. We will also wash the conical flask each time I do an experiment. To decide on the values of variables we will keep the same we have carried out preliminary experiments.
The first preliminary experiment we carried out was to find the mass of chips to use and this experiment was also used to test the range of concentration to use in the experiment. These experiments were important to carry out because we could make sure the reaction did not fill up the cylinder too quickly leaving many times blank as the cylinder cannot contain all of the gas. This could also make sure the reaction did not take place too slowly to give us a small range of results.
To carry out the experiment we used a measuring cylinder and timed how long it took for the water to be exhaled up to 50cm³ due to the presence of gas. The volume of the measuring cylinder was 100cm³. We reacted both of the reactants in a conical flask and measured the mass of the chips on a electronic balance to get a fairly accurate reading.
My Preliminary results are shown underneath.
From this, I decided the best mass to use was 0.50, this was because it was fast enough to get a wide range of results but anything faster would make the experiment hard to record as the cylinder would be filled too quickly and anything Slower Would make my results inaccurate.
Method
To make the test a fair test we had to carry out the same method each time this is what we did.
First we filled the tub with tap water about half way up and filled the measuring cylinder with water and then turned the measuring cylinder upside down into the tub of water so the cylinder was still filled with water. By doing this we did create a slight margin of error because some of the water was displaced when doing this although it was very little. We changed the size of the cylinders, however, this did not make the test unfair. We then put the delivery tube under the cylinder so the air from the experiment could displace the water. To make sure the volumes of acid and water were right we now measured the volumes of each in a measuring cylinder to be accurate. To make sure the mass of marble chips were right we measured on the electronic balance to one decimal place. Then we put the chips and the acid in the conical flask and started the stopwatch.
Here are my results below:
While working all safety procedures were followed very carefully like the use of safety goggles and putting the bags under the table. The measurements I feel were fairly accurate as the results were what was expected. There was one anomalous result, however, which was repeated to get a more accurate result. We repeated the experiment three times so we could find averages and get more accurate results. The results were measured to the nearest centimetre cubed because this was the maximum accuracy of the cylinders. The results show the results we got for each experiment.
By doing a calculation similar to underneath all the results from the same concentration were added together and divided by three (the number of experiments). The anomalous result was not included in this, however, but the repeated result was.
To find the mean this calculation was used
first result + second result +third result
= Average
3
From these results we can conclude that by increasing the concentration of hydrochloric acid the reaction rate is increased. The increase does seem to be proportional, as the gradient of the line seems to decrease by roughly the same amount each time. This is shown underneath.
To calculate the gradient the method below was used.
Point on Y-axis
Point on X axis
From this the following Gradients were found
Concentration molars Gradient
2.0= 2.3
1.6= 1.9
1.2= 1.5
0.8= 0.9
0.4= 0.2
The results that were found were what was expected to a certain degree. The reaction rate did not seem to show any signs of slowing down though which is what was expected. This was probably due to the fact that the experiment was not timed for long enough though.
The fact that the reaction rate was highest at the highest concentrations shows that the higher the concentration the more particles that are present per set volume which shows increases the rate of reaction. This was not exactly followed in the experiment, which was probably due to a margin of error in the results, but the pattern was still showed. This also proves that activation energy does not play a part because if this did the gradients of the lines would not increase by the amounts they did. This is due to the fact more/less energy would be needed to start the reaction and there would be a higher or lower gradient of the line so the gradients would not go up /down by the same amounts.
The results that were derived from the experiments showed a pattern but the prediction that was made was not completely supported because the reaction rate did not show any signs of slowing down. There was one anomaly, however, but this experiment was repeated to give results that matched the pattern. It is not certain why this result was found but it was probably due to the mass of the marble chips being measured slightly inaccurately because we measured the mass of the chips to the nearest whole number this would account for a slight margin of error. Another possibility is because the surface was different for each chip the total surface area was different this would be very unlikely, however.
The measurements were accurate to about cm³ because this is how often the cylinders were marked.
The method did show the relationship between the concentration and the rate of reaction but there was a slight margin of error because when turning the cylinder upside down a small volume of water was lost. To solve this problem we could use a gas syringe but the problem with this is we could not test the higher volumes of gas, which would mean the range of results would be lower which would mean the pattern we got would be less obvious.
The experiments were fair tests to a certain extent but there was a certain margin of error because the results recorded were only to the nearest cm³ and the values of the controlled variables were not exact amounts so the may have been slightly differently each time which would have affected slightly the reliability of the results. This would have made little difference to the results though as the volume of gas was only measured to the nearest cm³.
To find if the prediction was supported or to find if the reaction rate did slow down after the time progressed the experiment could be timed for longer than two minutes. This would also enable us to find weather the pattern changed after a certain time or the reaction rate just generally slowed down and we found a curve when comparing the concentration of the acid and the calcium carbonate.
It was also not certain if the concentration keeps increasing the rate of reaction or this only happens to a certain extent. This could be found out by extending the range of concentrations reacted. These reactions would have to conducted very carefully though as hydrochloric acid of this concentration can be very dangerous.
To find out information for my investigation I used the resources listed below.
Internet- www.about.com
www.excite.co.uk
Books- Nelson Science
Collins science
Encarta
Encyclopaedia
