Mg + HCl Experiment Report Final PDF

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Investigation of the effect of Concentration the Chemical Rate of Reaction

Science - Rachel Champion 10B Teachers: Ms Aston & Ms Burton Draft Due: 9th March 2020 Final Due: 27th March 2020 Other Group Members: Charlie Gibson, Georgia Varvari

Research Question What is the effect of the concentration of hydrochloric acid on the rate of reaction with magnesium?

Rationale and Hypothesis If the concentration of hydrochloric acid increases then the rate of the chemical reaction with magnesium will increase because there will be more particles of the reactant in a smaller space, increasing the likelihood of successful collisions, leading to a faster reaction rate. Reaction Rate is the speed at which a chemical reaction proceeds[ CITATION Kei18 \l 1033 ]. Collision theory states that for a chemical reaction to occur, the reacting particles must successfully collide with one another with sufficient energy to break the bonds. Thus, the rate of the reaction depends on the frequency of successful collisions[ CITATION Sim19 \l 1033 ]. In the experiment that will be conducted, the concentration of hydrochloric acid will increase in each condition, to investigate the effect concentration has on the rate of reaction. Concentration is the amount of a chemical in a certain volume of liquid or gas which can be altered by diluting or concentrating a solution[ CITATION Gre \l 1033 ]. Increasing the concentration is a very common way of increasing the rate of reaction as particles are more likely to collide and therefore more reactions will occur. Collisions are necessary for a reaction to occur so the reactants can rearrange and form new products (see figure 1). Concentration will be increased for each condition in the experiment, by decreasing the dilution of the hydrochloric acid. The reaction that will take place when the magnesium will be added to hydrochloric acid will Figure 1: Effect of increased concentration on the rate of produce magnesium chloride and reaction[ CITATION Gre \l 1033 ] hydrogen gas, written in the form Mg(s) + 2HCl(aq) --> MgCl2(aq) + H2(g)[ CITATION Gre \l 1033 ]. After research of the reaction between acids and metals, it is predicted that the reaction will produce increasing linear data when plotted on a graph[ CITATION Ber18 \l 1033 ].

Identifying Variables

Variable

Type (independent, dependent, controlled)

Values Selected and details of Management/Measurement (e.g. specific volumes, concentrations, measurements, temperatures, etc)

Rate of reaction

Dependent

milligram/seconds

concentration of hydrochloric acid

Independent

0.75M, 1M, 1.5M, 2M

The volume of the test tube

Controlled

20mL

Quantity/Mass of magnesium

Controlled

Controlled mass of Mg – 14mg and 15mg

Temperature of reactants

controlled

The experiment conducted in an airconditioned environment - thus, controlled

The volume of Hydrochloric Acid

controlled

ml

Unit of time reaction is measured in

Controlled

Seconds

What’s considered the end of the reaction

Controlled

No more bubbles produced, the solution still and clear, magnesium gone

Measurement tools for hydrochloric acid and magnesium

Controlled

Same measuring cylinder, stopwatch and scales

Methodology In the original method “Reactivity of Period 3 metals”, 8mL of hydrochloric acid was added to a test tube and a piece of magnesium was dropped into the acid. A stopwatch was then used to time until all the magnesium had fully reacted. Some changes have been made to the original method, to ensure that the experiment and data collected is more accurate and precise. In the modified

experiment, 3 trials will be conducted of 4 conditions of varying concentrations. With the varying concentrations of 0.75M, 1M, 1.5M and 2M, the most accurate and precise result of the effect of concentration will be given. Lastly, in the original experiment, random, unweighed pieces of magnesium were used in the trials. To make the experiment more precise, each piece of magnesium will be weighed, so that all trials are conducted with the same conditions and it is a controlled variable.

Management of Risk The modified experiment is considered of medium risk. This level of risk will be controlled by taking various measures in order to maintain the safety of the group members. The three major hazards of the experiment are broken glass, hydrochloric acid and magnesium. To prevent an accident or harm safety glasses will be worn, preventing any dangerous solutions or broken glass from entering the eye. Also, a lab coat will be worn to avoid any solutions splashing on the skin, which could irritate. Additionally, the lab coat will provide protection for the experimenters from getting cuts from broken test tubes. Another precaution that will be taken during the experiment is placing the test tubes in a rack in the middle of the bench to prevent them from being knocked off the bench and smashing.

Results The concentration of Hydrochloric acid (M/L) 0.75

Mass of Mg before Reaction (mg) Trial 1

14

Time of Reaction Rate of Reaction Mean Reaction (secs) (mg/sec) Rate (mg/sec) 338.6

0.0413/sec

0.0417/sec

Trial 2

14

346.97

0.0403/sec

Trial 3

14

321.34

0.0436/sec

           

Observations

1

Trial 1

14

102.5

0.1366/sec

Trial 2

14

108.72

0.1288/sec

Trial 3

14

103.41

0.1354/sec

 

Observations

1.5

14

68.66

0.2039/sec

Trial 2

14

70.03

0.1999/sec

Trial 3

14

63.62

0.2201/sec

        

0.1336/sec

Quite similar observations for 0.75M and 1M concentrations faint, slow reaction

Trial 1

Observations

2

Slow reaction Fizzing noise Bubbling- only mildly though Magnesium sunk to the bottom of a test tube Translucent but progressively cloudy Light condensation on test glass No heat produced Magnesium floated to the top and moving slowly around Solution clear again at the end of the reaction Light odour produced See smoke faintly (note: Touched the test tube to feel for heat production, could be considered agitation)

0.2077/sec

Immediate reaction with large bubbling Mg rotating rapidly Fizzing loud The smoke produced in bursts Condensation on test tube above solution Cloudiness at the top, translucent at the bottom Mg didn’t sink stayed at the top Significant heat produced Strong odour

Trial 1

15

53

0.2830/sec

Trial 2

15

50.69

0.2959/sec

Trial 3

15

53.41

0.2808/sec

0.2866/sec

Observations

       

Very rapid production of bubbles Cloudy on top of the solution Continuous Smoke produced Fizzing sound very loud Condensation on upper test tube Mg moving around rapidly on top of the solution A large amount of heat produced around where reaction took place in the test tube A very strong odour produced

Qualitative Observations: After conducting the experiment, and observing the differences between the reactions of each concentration, it was witnessed that as the concentrations increased, the bubbles became more vigorous, more heat was produced, the smoke produced became continuous and the odour produced became stronger.

Data Processing – Calculations Table 1: Measurement Uncertainty Measurement Uncertainty Measuring Cylinder ±0.1ml Electronic Balance ±1mg Stopwatch ±0.3secs

Table 2: Percentage Measurement Uncertainty Electronic Balance Reading (mg) 14 15 Absolute Mean Uncertainty (%) Stopwatch Trials 0.75M HCl concentration Trial 1 Trial 2 Trial 3 1M HCl concentration Trial 1 Trial 2 Trial 3 1.5M HCl concentration Trial 1 Trial 2 Trial 3 2M HCl concentration Trial 1 Trial 2 Trial 3 Measuring Cylinder Reading (ml) 8

Percentage measurement uncertainty (%) 7.1429 6.6667

Percentage measurement uncertainty (%) 0.0886 0.0865 0.0934 0.2927 0.2759 0.2901 0.4369 0.4284 0.4715 0.5660 0.5918 0.5617 Percentage measurement uncertainty (%) 1.2500

Table 3: Absolute Mean Uncertainty and Percentage Mean Uncertainty Rate of Reaction Trials (mg/sec) 0.75M HCl concentration Trial 1 0.0413 Trial 2 0.0403 Trial 3 0.0436

Mean reaction rate

0.0418

Absolute Mean Uncertainty (±) 0.00165

Percentage Mean Uncertainty (%) 3.9474

1M HCl concentration Trial 1 Trial 2 Trial 3 1.5M HCl concentration Trial 1 Trial 2 Trial 3 2M HCl concentration Trial 1 Trial 2 Trial 3

0.1366 0.1288 0.1354

0.1336

0.0039

2.9192

0.2039 0.1999 0.2201

0.2080

0.0101

4.8558

0.2866

0.00755

2.6343

0.2830 0.2959 0.2808

Calculation Examples: Percentage Measurement Uncertainty – 0.75M Trial 1: Stopwatch

0.3 ×100=0.0886 % 338.6

Reaction Rate – 0.75M Trial 1

14 =0.0418 338.6

Mean Reaction Rate – 0.75M Concentration HCl

338.6 + 346.97 + 321.34 =335.6367 3

Absolute Mean Uncertainty – 0.75M Concentration HCl

0.0436−0.0436 =±0.00165 2

Percentage Mean Uncertainty – 0.75M Trial 1

0.00165 ×100=3.9474 % 0.0418

Graphs of Experimental Data Graph 1: Linear trendline

The effect of concentration of Hydrochloric Acid on the Rate of Reaction Rate of Reaction (mg/sec)

0.3500 0.3000 0.2500

f(x) = 0.19 x − 0.08 R² = 0.97

0.2000 0.1500 0.1000 0.0500 0.0000 0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

Concentration of HCl (M)

Graph 2: Logarithmic trendline Graph 3: Exponential trendline

Discussion After analysing the data collected during the experiment, it can be concluded that the results support the hypothesis. As a result of the increased concentration, the rate of the reaction increased in each condition with a few minor fluctuations. For example, in the 0.75M concentration trials, the mean rate of reaction was 0.0418/sec compared to the 1.5M concentration trials where the mean was 0.2080/sec. The increase in concentration, also caused alterations in qualitative observations. The bubbles were more vigorous, with an increase in heat and odour production and the smoke produced being continuous. Additionally, the data collected was graphed to provide a greater understanding of the pattern of the data. In graph 2, Logarithmic trendlines, it can be observed that the data increased steadily and mildly plateaued at the 1.5M concentration with the final rate of reaction of the experiment being 0.2866/sec for 2M concentration. Trendlines were then added to the graphs, to identify the best trendline which best represented the rate of change. In Graph 1, 2 and 3, linear, logarithmic and exponential trendlines have been included to identify the best trendline for the data. The best fit for the data is the logarithmic trendline, with the r2 value of 0.9893 closest to 1. Since this value falls above 0.9, there, therefore, is a strong relationship between the independent and dependent variable in the experiment as the plotted data is quite close to the trendline. Thus, the logarithmic trendline best describes the data. The logarithmic trendline especially shows the rate of reaction increase steadily between 0.75M and 1M and then plateauing between 1.5M and 2M. Thus, this trend supports the hypothesis in both its direction and pattern. When experimenting, the trials were carried out with as much precision and accuracy as possible. However, with the limitations of the measuring instruments and the production of random errors such as equipment limitations and unpredictable fluctuations, the estimation of last digits in calculations and experiment error, this could not be ensured. As displayed in Table 2: Percentage Measurement Uncertainty, the measurement uncertainty for the measuring cylinder is 1.25%. Additionally, the percentage measurement uncertainty for the stopwatch for trial 1 of 0.75M concentration was calculated to 0.0886 and for trial 3 of 2M

concentration is 0.5617%. It is evident that as the rate of reaction increases, the percentage measurement uncertainty also increases steadily. The percentage mean uncertainty of 0.75M concentration is 3.9474% and for 2M concentration is 2.6343%. As the measurement uncertainty of the stopwatch and measuring cylinder are much smaller than the mean uncertainty of all trials, this suggests that they were not significant contributors to the overall uncertainty of the experiment. With all percentage mean uncertainty’s calculating to under 5%, the experiment is deemed extremely precise, and the data fairly reliable. However, the measurement uncertainty of the measuring balance was much higher than all the other uncertainty’s, calculating to 7.1429% for 14mg and 6.6667% for 15mg. This inaccuracy of the measurements was because the experiment was conducted in a high school science laboratory, with the most accurate electronic balance having an absolute uncertainty of ±1mg. Thus, this would have affected the overall, calculations of the rate of the reaction of each trial and precision of the experiment. Another major limitation of the experiment was that only four concentrations of hydrochloric acid were supplied. This sample sized decreased the overall accuracy of the experiment and did not provide a sufficiently accurate view of the trend and pattern of the rate of reactions as concentration increase.

To improve the overall accuracy and precision as well asreduce the errors of the experiment, a more accurate electronic balance could be used, and the extension of more concentrations of hydrochloric acid could be trialled. Since the accuracy of electronic balances in the school laboratory environment were not the most precise in providing the weights of the magnesium, an external electronic balance would need to be used, for example, one with an absolute measurement uncertainty of ±0.01mg. Additionally, extending the experiment by trialling more concentrations, for example, 2.5M and 3M hydrochloric acid, it would provide a more accurate view on the effect of concentration of the rate of reaction and the overall nature of trend produced. Therefore, by implementing these improvements and extensions, the accuracy and precision of the experiment would improve. It would result in a larger collection of data that would provide a broader understanding of the trend and the effect that concentration has on the rate of reaction.

References Fraser, S., & Lawson, P. (2019, September 30). The Collision Theory. Retrieved from Chemistry: Libre Texts: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Ma ps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Kinetics/Modeling_Reacti on_Kinetics/Collision_Theory/The_Collision_Theory Helmenstine, A. M. (2019, May 8). Concentration Definition (Chemistry). Retrieved from Thought Co: https://www.thoughtco.com/definition-of-concentration-605844 Laidler, K. (2018, May 17). Reaction Rate. Retrieved from Encyclopaedia Britannica: https://www.britannica.com/science/reaction-rate

Markgraf, B. (2018, May 12). How Does Concentration Affect the Rate of Reaction? Retrieved from Sciencing: https://sciencing.com/how-does-concentration-affect-the-rate-of-reaction13712168.html Rickard, G., Clarke, W., Devlin, J., Linstead, G., Madden, D., Maher, F., . . . Tilley, C. (2017). Pearson Science 10 AC. Retrieved from Box of Books: https://msmcollege.boxofbooks.io/book/EBE55770-AB1C-11E8-B6F81A424E975647/webreader2

Appendices Method for the original experiment 1. 2. 3. 4. 5. 6. 7. 8.

Measure 8 mL of hydrochloric acid with the measuring cylinder and add to the test tube. Use tweezers to drop the piece of magnesium into the acid. Start the stopwatch when the magnesium hits the acid. Stop the stopwatch when all the magnesium has fully reacted. Record observations. Record the time taken for the magnesium piece to be fully reacted. Briefly rinse the test tube. There is no need to rinse the measuring cylinder. Repeat steps 1-7 twice with fresh pieces of magnesium and a fresh 8 mL of hydrochloric acid.

Planning Sheet Group Members: Georgia Varvari, Charlie Gibson

Research question: What is the effect of concentration of hydrochloric acid on the rate of reaction with magnesium?

Hypothesis: If the concentration of hydrochloric acid increases then the rate of the chemical reaction with magnesium will increase because there will be more particles of the reactant in a smaller space, increasing the likelihood of successful collisions, leading to a faster reaction rate.

Variables:

Variable

Type (independent, Values Selected and details of dependent, Management/Measurement controlled) (e.g. specific volumes, concentrations, measurements, temperatures, etc)

Rate of reaction

Dependent

milligram/seconds

concentration of hydrochloric acid

Independent

0.75M, 1M, 1.5M, 2M

The volume of the test tube

Controlled

20mL

Quantity/Mass of magnesium

Controlled

1 piece of Mg, measured in Grams

Temperature of reactants

controlled

The experiment conducted in an airconditioned environment - thus, controlled

The volume of Hydrochloric Acid

controlled

ml

Unit of time reaction is Controlled measured in

Seconds

What’s considered the end of the reaction

No more bubbles produced, the solution still and clear, magnesium gone

Controlled

Measurement tools for hydrochloric acid and magnesium

Controlled

Same measuring cylinder, stopwatch and scales

Modifications on original ‘Reaction time of magnesium and hydrochloric acid’ experiment: The modification we've made is to change the concentration of hydrochloric acid in the experiment. For each trial, the concentration will be increased to investigate the effect concentration has on the reaction time of magnesium. With the varying concentration: 0.75, 1, 1.5, 2 moles. Additionally, we extended the method of the original experiment so that 3 trials were conducted of the 4 concentrations of hydrochloric acid. This was changed in order to give us the most accurate and precise results of the effect concentration has on the rate of reaction.

Results table: The concentration of HCl (moles)

Trial 1

0.75 1 1.5 2

Trial 2

0.75 1 1.5 2

Trial 3

0.75 1 1.5 2

Mass of Mg before reaction (g)

The time recorded of Reaction (secs)...