Magnesium and dilute hydrochloric acid are both common chemicals found in school laboratories.
When these two chemicals are mixed together a chemical reaction takes place that produces bubbles of hydrogen gas.Magnesium + Dilute Hydrochloric acid = Magnesium chloride + HydrogenMg(s) + 2HCL(aq) = MgCl2 + H2In this investigation I will attempt to change the speed of this reaction by altering a key factor.PlanThere are several factors that will affect the speed of the reaction that I will carry out. They are:* The concentration of the hydrochloric acid.* The temperature of the hydrochloric acid.* The surface area of the magnesium.* The adding of a catalyst.From these 4 factors I have chosen to investigate the concentration of the hydrochloric acid.
As I have chosen this factor, I must pay careful attention to keeping the other factors constant. In my table below I have shown how I will control the other factors:FactorHow I will keep it the sameVolume of hydrochloric acidI will use a measuring cylinder to measure 25cm3Volume of hydrogen collectedAlways collect using a burette and delivery tubeAmount of magnesium ribbonUse a ruler to measure the lengthSurface area of magnesium ribbonAlways use a ribbon of magnesiumTemperature of hydrochloric acidUse a thermometer and take the temperature every minutePredictionI predict that when I increase the concentration, the speed of the reaction will increase. The reason for my prediction is stated in my scientific explanation.For a reaction to take place we need collisions between the acid particles and the magnesium. In the diagram above there are only 2 acid particles and we will get a few collisions with the magnesium.
This will produce hydrogen more slowly.In the 2nd diagram there hare twice the number of acid particles, which means twice the collisions with the magnesium, therefore more hydrogen is produced.ApparatusUseBuretteMeasuring the amount of hydrogen producedBurette HolderHolding the burette securely in placeClamp StandTo hold the burette holder and the burettePlastic TroughFilled with water to prevent hydrogen escapingStopwatchTo time the reactionMeasuring cylinderTo measure accurately the amounts of acid and waterDelivery tubeTo carry the hydrogen into the buretteThermometerTo ascertain the temperature every minuteProtective gogglesTo protect eyes from being harmed by the reactionConical flaskTo carry out the reactionRulerTo measure the length of the magnesium ribbonApparatusDiagramMethod1. Firstly, I set up all the apparatus as shown above in the diagram.2. Then I filled the burette to the top with water and turned it upside down in the trough of water, trying not to let any air inside the burette.
3. I then secured the burette in place using a burette holder and a clamp stand.4. I placed a delivery tube up the burette, while placing the other end in a conical flank, held in by a bung.
The conical flask is where the reaction will take place.5. Following this, I prepared 25cm3 of 2 molar Hydrochloric acid and a 2cm piece of magnesium ribbon.6. I double-checked that everything was prepared and made sure I had a stopwatch and a reliable results table to record my results.7. Then I placed the magnesium ribbon and the 2M Hydrochloric acid into the conical flask, (in that order), began the stopwatch and recorded my results every 5 seconds.My preliminary results are displayed below.
Concentration (M)Volume of Hydrochloric Acid (cm3)TimeVolume of Hydrogen (cm3)Length of Magnesium2255522251011222515112225201122252511222530112These results show me that using a 2cm piece of magnesium will produce a set of very unreliable results. These results below show that an 8cm piece of magnesium would be much more reliable as this is only with 0.5 Molar acid:Volume of Hydrogen (cm3)Time (seconds)1st attempt2nd attempt3rd attemptAverage000001032432076773011910104013.512131350171616166020181819So, my preliminary results tell me that I would attain the best results using and 8cm piece of magnesium.
I will be able to vary the concentration to see how the reaction speeds up and slows down.All of my results are displayed on the next page. Each attempt displays the amount of Hydrochloric acid collected in cm3:Results0.50MVolume of Hydrogen Collected (cm3)Time(s)1st attempt2nd attempt3rd attemptAverage000001032432076773011910104013.
5121313501716161660201818190.75MVolume of Hydrogen Collected (cm3)Time(s)1st attempt2nd attempt3rd attemptAverage00000109788201715151630242223234030292829503637333560424341421.00MVolume of Hydrogen Collected (cm3)Time(s)1st attempt2nd attempt3rd attemptAverage00000101013111120212623233035393336404751454850566157586062656464In a first attempt, the stronger acids of 1.
25M and 1.5M used up the Magnesium quicker, proving difficult to measure every 10 seconds. I decided to measure every 5 seconds instead to increase the accuracy of my results.
1.25MVolume of Hydrogen Collected (cm3)Time(s)1st attempt2nd attempt3rd attemptAverage00000525202222104035383815505052512060616161256669696830717271713571737172407173717245717372725072737373557274737360727473731.50MVolume of Hydrogen Collected (cm3)Time(s)1st attempt2nd attempt3rd attemptAverage0000052928302910505251511565676666207372747325767577753079787979357880797940808280804581848282508284838355828583836083858384AnalysisJudging by my results, when I increased the concentration of hydrochloric acid, the reaction went faster.A more visual representation is included on my graph attached to this sheet of results.
It displays a line for each of the 5 molarities. Also included on the graph is a gradient line, drawn on each molarity line. I can use this gradient line to work out the initial rate of the reaction. I have done this for each line to calculate the initial rate. Below is a table of the rate for each concentration.
I will draw a graph of this also. The equation for working out the rate is y/x, where y = volume of HCL and x = time.Rate of reaction = volume of hydrogentimeRate (cm3/s)Concentration (M)0.30.500.80.751.
11.003.81.255.11.50The reason for this pattern in my results is all to do with particles and collision theory, as I have previously mentioned.
In this diagram of 1M acid, there are 2 acid particles (H+ ions) and 2 water particles. Because of this, there is less chance of a reaction taking place between the acid and the magnesium. There will only be a few collisions.
25cm3 2M acidIn the diagram above there are now twice as many acid particles, so the chance of reaction is greater and there will be many more collisions.My average result for 1M acid after 60 seconds is 64 seconds, which is considerably slower than my average result of 84 seconds for 2M acid after 60 seconds. Why this happened is all down to particle theory, explained above. This proves that higher molar acids have many more particles (H+ ions) that lower acid particles and this is why they react faster.EvaluationI think my experiments went as well as could be expected.
I feel that I attained a high degree of accuracy when recording results. My results portray the effect of collision theory well and explain how higher molar acids react faster than lower molar acids.I did not notice any anomalous results but on my graph 1.25M and 1.
5M had a considerably larger initial rate that the other concentrations and if I carried this investigation on I would probably look into this further.To improve my results yet further, a gas syringe could be used to collect the gas instead of a measuring cylinder. This would improve the accuracy of my results because less hydrogen can escape from the gas syringe as would in our experiment.
During class time, my teacher carried out an experiment analysing how concentration affects the speed of chemical reaction. He used calcium carbonate chips and various concentrations of HCL. The diagram and results are displayed below: