- For the purpose of my experiment I am going to do all the experiments at room temperature to make sure it is a fair test so that I will get accurate results.
- I will use exactly 2cms of magnesium ribbon each time to make sure that the surface area stays constant.
- The volume of the solution will be kept fair by using 70cm3 each time.
- The same strength acid of 1 unit will be used for each experiment.
- I will take readings at equal intervals and keep the same duration for each experiment to make sure they all have a fair amount of time for the reaction to occur.
This table below tell us the variables and the non-variables in the experiment:
Fair Test
Fair testing should play a big part in this experiment. If this experiment is not a fair test, we will be obtaining the wrong results, which could lead us to the wrong conclusions.
First of all, and most importantly, we will have to get the measurements of the solutions and the length of the magnesium ribbon as exact, and as accurate as possible. I will try and get the measurements of the magnesium as accurate as possible for every single experiment by evenly cutting the ribbon, and making a record of the length to the nearest millimetre. And I will be using a ruler so that we can get the best readings possible.
To make sure that the volume of the hydrochloric acid and the distilled water is as accurate as possible I will be using a burette to measure it out. I will then mix the two solutions in a measuring cylinder to re-check that the solution is exactly 70cm3 before pouring it into the conical flask. If the volume of one solution in a beaker is higher or lower than another, will affect the pattern of results later on. I will also make sure that the strength of the acid is 1 unit each time as a stronger/weaker acid will increase/decrease the rate of reaction and will affect out results.
I will make sure that the magnesium ribbon is fully submerged in the solution to make sure that the reaction can fairly take place
Carrying out the experiment in a constant temperature for the whole of the experiment is important. And to avoid temperature change, which might affect the two different sets of results, we will take the temperature of the room into account.
I will also repeat the whole experiment to make sure my results are accurate so that I have a fair and precise conclusion. Because I have a limited time to complete this investigation, I will only be repeating it once. However, if I had more time I would repeat it further to obtain even more accurate results.
Another important factor of a fair test is to start and stop the clock as quickly as possible. This meaning that we should start the clock as soon as the magnesium ribbon is put inside the flask, and to take readings exactly at 10-second intervals up to 40 seconds.
I will be checking for leaks in the gas syringe before each experiment as it can affect the readings of the CO given off in the reaction and therefore affect my results. I will also make sure that it reads at 0 at the beginning of the experiment also making the readings as accurate as possible. Also small things such as a dirty conical flask, and a slightly cracked measuring cylinder could still affect the results, and therefore we will take these into account as well.
If all of the precautions are done correctly then the experiment will be fair and so the results will be accurate and so we can get precise conclusions.
Hypothesis
From looking at my preliminary results and graph, and using background knowledge, I predict that the larger the concentration (i.e. the less water added) the quicker the rate of reaction will be (i.e. more C0 will be collected faster). This is because increasing the concentration of a substance in solution means that there will be more particles per dm3 of that substance. The more particles that there are, the more will collide per second, and so the rate of the reaction increases. This means more gas will be given off quicker into the gas syringe. This is an exothermic reaction. When there is only distilled water in the beaker, I think that there will be to no reaction-taking place with the magnesium ribbon, as water does not react with it. However, when there is no water in the solution and only hydrochloric acid. I think that the reaction will be very fast and the magnesium ribbon will dissolve within seconds.
Apparatus
- 600cm3 of hydrochloric acid
- 30cms of magnesium ribbon
- Scissors- to cut the magnesium ribbon
- Ruler- to measure the magnesium ribbon
- Gas syringe and bun- to collect gas given off in the reaction
- Measuring cylinder- to measure acid
- Conical Flask- to hold the solution
- Thermometer- to record the temperature of the room
Diagram
Risk assessment
Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. And that is why we take this into consideration, no matter what.
As we will be using acid, I will make sure I will be wearing a science overall to protect my clothes and goggles to protect my eyes. I will wash my hands after handling the acid as well, just in case my hands become in contact with my mouth or eyes post experiment. I will make sure all bottles, flasks and the gas syringe are safely on the table to prevent them falling off and smashing on the floor. Also, because the gas syringes are very delicate I will make sure that the clamp is not fastened too tightly as it can break the syringe. I will also be careful when using the scissors to prevent cuts.
Method
- Record the temperature of the room using a thermometer and record it down.
- Place the gas syringe into the clamp as shown in the diagram, making sure it is safely secure but not too tight as it can damage the equipment. Check the syringe for any leaks by pulling it and seeing if it goes back to 0. Make sure that is at 0 to begin with.
- Using a burette, measure out 70cm3 of hydrochloric acid. Then pour it into a conical flask.
- Next, using a ruler, cut 2cms of magnesium ribbon.
- Drop the magnesium ribbon into the flask of solution and quickly place the bun on the top and start the clock.
- Every 10 seconds take a reading off the gas syringe and note it down until 40 seconds has gone past.
- Repeat instructions 2-5 but with diluted HCl (i.e. mixed with H0). Using 10cm3 of H0 more each time and using 10cm of HCl less each time until you end up with just 70cm3 of H0.
- Repeat the whole experiment again so that you can make sure that all of the results are similar, and so that you will be able to take the average of the two experiments. This makes sure that you get accurate results. Repeating the experiments are important, because we will be able to receive valid results, and look for any anomalous results. Not to mention that we will take the fair testing into account.
OBTAINING EVIDENCE
During my experiment I took readings at exact intervals of how much hydrogen had been given off. I kept this constant to make sure that it was a fair text. When obtaining my results it was all done in room temperature, 25, so that this did not affect the rate of reaction. However as room temperature does differ, I took a reading of the temperature for both experiments.
Table of results
In the table below, it shows the ‘mass´ column, which is the weight of the magnesium before the experiment. There then is the amount of HCl used in each experiment. Each time the amount of HCl decreased by 10cm3 starting from 70cm3. The next column is the amount of water used for each experiment. However the increased by 10cm3 starting from 0cm3. After 10 seconds I took my reading of how much hydrogen was given off. I did this for the following 10-second internals up to 50secs. Each reading is to the nearest ml3.
EVALUATION AND CONCLUSION
Conclusion
In this experiment, I believe that I have collected enough data to support my hypothesis. This investigation was, I think, successful. Successful meaning my results collaborated my predictions.
This experiment shows rate of reaction of a magnesium strip in varied concentrations of hydrochloric acid and water. When magnesium was added to the solution with the most hydrochloric acid and with the least water in, the magnesium strip began to react more violently and more quickly. It gave out lots of bubbles and began to tarnish and lots of hydrogen was given off. However when it was put in a solution of only water it did not react at all. When there was 40cm3 of HCl and 30cm3 of H20, there was a reaction but it was much more slow and less hydrogen was given off. This is because increasing the concentration of the substance in solution meant that there would be more particles per dm3 of that substance. The more particles that there were, the more will collide per second, and so the rate of the reaction increases. This meant more gas will be given off quicker into the gas syringe. From my results I can also determine an equation:
Mg + HCl MgCl +H
Looking at my results
Looking at the results I can see that my investigation was fully accomplished, and was an achievement. I can tell this because my results coincide with my hypothesis that the larger the concentration or hydrochloric acid, the quicker the rate of reaction will be. I think that my results have been fairly accurate due to my careful precautions I took, to make sure that a fair test took place. However, on the colder day when the room temperature was 4 degrees colder, from looking at my graph, I can see that the rate of reaction was slightly slower. This is because when it is colder the particles move slower which decreases the number of collisions and therefore slow down the rate of reaction. To improve this, in future experiments I could control the room temperature by using controlled heaters. However from looking at my individual graph I can see that there are no obvious anomalous results.
The graphs and the results show that:
- Factors affect the rate of reaction.
- The larger the concentration or hydrochloric acid, the quicker the rate of reaction will be
- That temperature affects the rate of reaction
Evaluation
I followed the plan correctly; I believe I gained accurate and sufficient enough results to conclude the experiment, and to prove my hypothesis. My final results were fairly reliable, due to the precautions I took to make this a fair test.
Changes to plan
- I did not use a burette to measure out my solutions as it took too much time. Instead I used a measuring cylinder and measured to the nearest cm3.
- Also where Carbon Dioxide was said to be the gas given off, it is actually hydrogen