Scientific knowledge
When a chemical reaction occurs, the particles which combine need to meet up with each other (collide) so that they can swap or share electrons. If you want to speed up a reaction, you need to get these particles to hit each other more frequently. If the solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules, which make collisions between the important particles more likely.
In order to make my result precise and reliable I will need to take 3 repeats for every condition I need to do this so I can discard any anomalies and will need to keep the following the same every time I perform the experiment: -
- Temperature of the acid the same.
- Volume of acid used (cubic centimetres)
- Surface area of the magnesium.
- Weight of magnesium
- Clean the magnesium with emery paper before experiment.
- The length of magnesium must be the same.
Fair Test
The factors I will keep the same are: -
The temperature of the acid will need to be kept the same. I will need to keep the temperature the same because the temperature effects how much energy the atoms the more energy they have the more they will vibrate this will cause more collisions and a fast reaction rate than colder acid. I will keep this factor the same by leaving the test tube in a water bath, which I will keep at 30 degrees Celsius I will make sure it is kept at 30 degrees Celsius using a thermometer. I could alternatively use a thermostatic water bath.
I will need to keep the volume of acid the same I will need to do this because the more acid there is the more acid particles there are for collisions with the magnesium the more acid there is the more collisions there will be.
I will need to keep the surface area of the magnesium the same each time, if more surface is exposed in some experiments than others the more acid molecules will be able to react with the magnesium at the same time. If the surface area is bigger the rate of reaction would also be faster.
The weight of the magnesium will need to be kept the same so there is the same amount of magnesium each time for the same amount of collisions in every experiment.
I will need to clean every piece of magnesium for every experiment.
The length of magnesium must be the same.
Apparatus
25 pieces of magnesium ribbon.
Safety goggles
Hydrochloric acid (1 molar, 2molar)
Distilled water
Water (to dilute acid)
10ml test tube
Retort stand
Clamp
25 cm cubed measuring cylinder
Stop clock (sensitivity 1/10s)
Prediction
I predict that as the concentration of acid increases, the speed of the reaction will increase therefore the gas will be emitted faster. I think this because chemical reactions take place by chance. Particles need to collide with enough velocity so that they react there is a certain amount of energy needed for this however. When there are more acid particles in higher concentration acids more collisions can happen at the same time making the reaction happen quicker. In my experiment this will mean more hydrochloric acid molecules will collide with the surface of the reactant which is magnesium ribbon. In my experiment I predict that 0.2 molar will be least reactive followed by 0.5 molar then 1.0 molar, 1.5 molar and the most reactive will be 2.0 molar.
Graph here
Experiment 1
Experiment 2
Experiment 3
Table of averages
To work out the average hydrogen gaz produced I have to add up the repeats and divide them by three
Experiment 1 = x
Experiment 2 = y
Experiment 3 = z
x+y+z = Average
3
Graph here
Analysing and Considering Evidence
My results clearly show a pattern that the higher the concentration (molar) of acid the quicker the reaction occurs however although the speed of the reaction is faster this does not affect the amount of hydrogen gas released because the number of magnesium atoms are the same in each experiment. The reaction occurs faster with a higher concentration of acid because there are more acid atoms to collide with the magnesium atoms.
For condition 0.2 molar hydrochloric acid the reaction was very slow this is because in the 0.2 molar hydrochloric acid there are fewer acid atoms which means that less collisions with the magnesium ribbon can happen in the same time as a higher concentration of acid. This made 0.2 molar hydrochloric the slowest reaction in my results.
For condition 0.5 molar hydrochloric acid the reaction was still slow however it was faster than the 0.2 molar hydrochloric acid. This is because in the 0.5 molar hydrochloric acid the concentration is greater than then 0.2 molar acid. This means that more collisions with the magnesium ribbon can happen with the 0.5 molar acid than the 0.2 molar acid. This made 0.5 molar hydrochloric the second slowest reaction in my results.
For condition 1.0 molar hydrochloric acid it reacted faster than both 0.2 and 0.5 molar hydrochloric acid. This is because it is more concentrated than 0.2 and 0.5 this means that the solution contains more hydrochloric acid atoms for more collisions this means that all of the hydrochloric acid atoms and magnesium atoms of can become stable more quickly than the 0.2 molar and 0.5 molar acid.
For condition 1.5 molar hydrochloric acid this reacted faster than all the previous acids because it has a higher concentration causing more collisions than any of the others. This is what made the reaction occur faster and give of the hydrogen more rapidly.
For condition 2.0 molar hydrochloric acid this was the largest concentration of acid we used the hydrogen was given off faster than in any of the previous experiments due to its large amount of hydrochloric acid atoms to collide with the magnesium ribbon. This acid gives the hydrogen gas off the quickest.
I have compared these results and analysis with my prediction and they coincide, my prediction was correct because of the known scientific knowledge which I based it on.
Evaluation
In my experiments there were a number of sources of error: -
Temperature – The temperature control was a source of error. my experiments were performed in a room with another 30 people in through out the duration of the experiments the room was being heated from the respiration of the people in the room. This could have effected the experiment by heating the hydrochloric acid and the magnesium so that the particles have more energy to collide with each other making the reaction happen faster. I could do the experiment in a room on my own to make this more accurate. Another source of error was the water bath, from start to finish of the experiment the water bath temperature would change to stop this I could use a thermostatic water bath.
Loss of hydrogen – In my experiment the hydrogen had to travel from the delivery tube through water and into a measuring cylinder. As hydrogen can dissolve in water a small amount of it will be lost as it goes through the water. I could have used a gas cylinder to measure the hydrogen instead, this way the hydrogen would not have to travel through water. However in doing this there would be another problem in a gas cylinder it is possible for the gas to be compressed this would give us an even bigger source of error.
Dropping the magnesium into the hydrochloric acid – It was very difficult to drop a piece of magnesium into the test tube and put the bung on before any gas escaped. I could make some kind of system to hold the magnesium above the hydrochloric that could drop it into the acid while the bung is on the test tube.
Magnesium oxide – Magnesium oxide was a problem in the experiment I had to remove the magnesium oxide use emery paper it was very hard to see if I had removed all of the magnesium oxide from every piece of magnesium.
Weight of magnesium – In my experiment I did not weigh the magnesium instead I measured it by length. If I had weighed it I would be able to make the sure the mass of the magnesium was the same each time so there were the same number of magnesium atoms for the number of collisions with the hydrochloric acid.
My results are correct, I know this because my results support my prediction which I based on known scientific knowledge. I have studied my results to try and find any anomalies that would affect my averages but I have not found any this indicates the good accuracy of my experiments.
My evidence is reliable enough to support a firm conclusion, this is because I performed three repeats for each condition all which come out with similar results and no anomalies as well as this my prediction was accurate. As well as this the results coincide with other experiments, which have been performed by professional scientists.
I could perform additional experiments changing different factors I could use different acids and different alkaline metals, I could also use different concentrations of acid. I could perform the experiments at different temperatures. I could also perform more repeats of the experiment I have already been doing.
Gary Lester 11 G
