Plan: I am going to react a chosen length of magnesium ribbon with a chosen volume of hydrochloric acid. I will measure the speed of reaction by timing how long a magnesium strip will react with a concentration of hydrochloric acid. I will then repeat the experiment with the other different concentrations of hydrochloric acid. I will quickly drop the length of magnesium into the test tube and start the stop clock to record how long it takes for the magnesium strip to react. I will repeat the experiments two more times and record these results too. I will find the average results, which will give a more reliable and reproducible.
I am going to react a chosen length of magnesium ribbon with a chosen volume of hydrochloric acid. I will measure the rate of reaction by collecting the hydrogen gas that is produced in a gas syringe that will be connected, via a piece of rubber tubing and a rubber cork to the conical flask that the reaction will take place in. I will quickly drop the length of magnesium into the flask and connect the rubber cork to it. I will then start the stop clock and record the volume of gas, which has evolved. I will repeat the experiments two more times and record these results too. I will find the average results, which will give a more reliable and reproducible.
Fair Test: To help keep the test fair I must:
- Make sure that each strip of magnesium is the same length and width, as a grater surface area causes a faster reaction, but can also slow the rate down as there is more magnesium to react with.
- Make sure the reactions happen at the same temperature; as if it was hotter the particles would move faster causing the particles to collide with each other more often and with greater energy.
- Make sure the same measurement of the different concentrations of acid is used (e.g. 3mls). As if you put more in there, there would be more particles to react with, then if the correct amount was used.
- Make sure that the different concentrations of acid don’t mix, as if they where it would change the concentrations of them. So to stop these, different measuring equipment must be used for each one.
- Make sure that different test tubes are used for each concentration, as this would stop mixing of different concentrations.
- Make sure that each strip of magnesium is total submerged into acid, so that a full reaction of the whole strip can happen at “once.”
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Make sure that the magnesium is cleaned with emery paper before experiment.
Safety: I will need to make my experiment as safe as possible as injury can be caused from the experiment which I am doing. The safety precautions I have to take are:
- Wear safety goggles
- If acid touches the skin or the eyes wash the area and consulate the teacher/doctor
- Make sure any broken glass is cleared properly, as glass in sharp
- Safe disposal of reagents and laboratory acid
Preliminary Notes:
Magnesium + Hydrochloric Acid Magnesium Chloride + Hydrogen
Mg + 2HCl MgCl2 + H2
1 mole Mg + 2 moles HCl 1 mole MgCl2 + 1 mole H2
24g + 73g 95g + 2g
Gas is not “supposed” to be measured in grams; we know that the approximant amount of any 1 mole gas at room temperature is 24,000 cm3. So…
Mg + 2HCl MgCl2 + H2
24g + 73g 95g + 24,000 cm3
From this I can predict that there will be 24,000 cm3 of hydrogen gas produced by the reaction above. We can see that magnesium is directly related to how much hydrogen gas is produced. I can find out how much hydrogen gas will be produced, if I know how many grams of magnesium there are, by using proportion.
Let’s assume that I used a strip of magnesium weighing 0.03 g If so, 0.03 g magnesium will produce (0.03/24) x 24,000 cm3 of hydrogen = 30 cm3 hydrogen
To calculate how much of magnesium and hydrochloric acid I will use in the experiment I need to look at the equation above. As hydrochloric acid is not directly related to how much hydrogen gas an excess amount can be used, more than is needed for the magnesium fully react with it. But this amount must be kept the same thought out the experiment for each. For example, 3mls of each concentration of acid. The amount of magnesium is directly related to the amount of hydrogen produced, so this needs to be able to react fully with the acid it is put in.
Preliminary Results: I have decided to use 3mls of acid in the first experiment and 10mls in the second. I will keep the magnesium constant though out both experiments, 1cm. These measurements of the reactants will give some good results. I have worked out that the magnesium will fully reacted with both amounts of acid.
Experiment: There are several experiments in which I could get my data, but here are the two which I am planning to do:
Amount of gas
I could use a gas syringe to collect the gas that will be given of by the reaction. These results could they be used to calculate the initial rate of reaction.
Time it takes for reaction
I could measure the length of time it takes for the magnesium to fully react with the acid. The only problem with recording my experiment this way is that I could only calculate the average rate of reaction and not the initial rate of reaction
Ways to measure the rate of the reaction
Average rate of reaction – This will be worked out when I find how long the magnesium takes to react.
Initial rate of reaction – This could be worked out from the amount of gas evolved.
Method:
1st test
- Measure 10ml of hydrochloric acid, which is at 0.5 moles, with the measuring cylinder.
- Place this into a test tube.
- Cut 1cm strip of magnesium by using a ruler and scissors.
- Place the magnesium strip into the acid and time (dependent variable) the reaction.
- Record the time.
- Repeat step 1-5 with the different moles of hydrochloric acid (independent variable).
- Repeat step 1-6 two more times to get a better set of data.
2nd test
- Measure 10ml of hydrochloric acid, which is at 0.5 moles, with the measuring cylinder.
- Place this into a conical flask.
- Cut 1cm strip of magnesium by using a ruler and scissors.
- Assemble the syringe, cork and delivery tube.
- Clamp this to a clamp stand, with a clamp, at a horizontal position.
- Place the conical flask under the cork.
- Put the 1cm of magnesium into the conical flask and put the cork into the top of the conical flask.
- Time the reaction for a minute, and record the result on the syringe (dependent variable).
- Repeat step 1-8 with the different moles of hydrochloric acid (independent variable).
- Repeat step 1-9 two more times to get a better set of data.
Table of Results:
1st test
2nd test
Human error and the equipment used needs to be taken into account when looking at how accurate the results are. The measurements of acid and magnesium strip were done with equipment which only gives the measurements to a millilitre/millimetre. Also it is humanly impossible to see that the measurements where correct with the naked eye. So the results are accurate as humanly possible.
Graphs of Result:
1st test
2nd test
Conclusion: The 1st and 2nd graphs show that the higher the molar the faster the reaction, and that the lower the molar the slower the reaction happens. So my prediction was correct! “The higher the concentration the more particles of acid there are, causing them to collide more frequently than the lower concentration, which has less particles of acid. Concluding that the higher concentration will collide with the substance more often, making the reaction faster. Also that the lower concentration will collide with the substance less often, making the reaction slower, than the higher one. The same idea of “it is quicker to dig a hole with 10 men than 1 man digging it by himself” can be put to this.” from prediction
Both graphs inform me that the second prediction was wrong! The first table shows that the reaction doesn’t double with double the concentrations. But it does show that the reaction time is quadruple when the concentration goes down from 2 to 1 mole.
Time in seconds:
1 mole = 96.66
2 mole = 23.06
23.06 x 4 = 92.24
As the experiment doesn’t provide us with 100% accurate results, due to human error and to inaccuracy of apparatus used, the above calculations are a bit off, but they are close. I can give my interruption of the results, taking in mind there inaccuracy, that if you go down by 1 mole the reaction time will quadruple, and visa-versa.
Evaluation: The experiments could have been conducted more accurate if the measurements where done by a machine, which would give us the correct measurements each time. If I have more time to conduct the “collecting gas” experiment, the results would have been much better, but we only had time to see how much was collected in one minute. The syringe was not total far as there is friction between the bit coming out and the outer shell of the syringe. This causes the gas to compress, meaning the syringe doesn’t give an accurate measurement. There are more accurate ways of measuring gas but the school doesn’t have the equipment to do it more accurately.
Other methods which I could have conducted, which would have helped me support my conclusion, included:
- Measuring the temperature of the reactions as it happens. Measurements could be taken, for example, every 30 seconds. These results will then be plotted on to a line graph, with each different mole having different coloured line; this will give a clear indication to each concentration. These results will tell us how fast the reaction is happening and how each one differs from the next. Also the time of the reaction would be recorded in line with each temperature taken, e.g. 30sec = 10c, 60sec = 12c, and so on.
Further work:
- I could do is to the experiment again but with different acids and see what kind of results I get. I could compare each set of acid results to find out which reacts the fastest with magnesium.
- Repeat the experiment but with different reactants. I could also use the less reactive metals of the reactivity series (zinc, aluminium, iron and lead) that way I could find the initial rate of reaction at 5 seconds for the higher concentrations of acid like 3.0M or 3.5M and I could find there relative activity.
