# How Does Acid Concentration Affect the Rate of Reaction?

2525 words (10 pages) Essay

18th May 2020 Chemistry Reference this

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RATIONALE:

Reaction rate, the speed at which a chemical reaction proceeds. The rate of reaction is the speed at which reactants are converted into products. A few things can affect the speed of the reaction and the overall amount of collisions that can occur. Such as, HCI acid concentrations, temperature, and catalyst properties if either are any at all. (Opentextbc.ca. (2019)) Chemical substances cannot react together unless the molecules, atoms or ions come into contact. (Chemistry LibreTexts. (2019)) If there is no contact, there will be no reaction or initial reaction rate. However, if there is more concentration of a chemical in an experiment, there is a more likely chance that the molecules will collide into one another and increase the rate of reaction this referred to as the “collision theory”. Thiosulphate was used because the product that is made after adding HCI into the solution goes opaque this is especially good because as the time it takes for the reaction to occur is easier to take down, the colour changing of the solution becomes helpful as to indicate when to stop the timer and get a somewhat accurate reading.

The reaction between sodium thiosulphate and hydrochloric acid is as follows;

REACTION 1: Na2S2O3(aq) + HCl(aq) → S(s) + NaCl(aq) + H2O(l) + SO2(g)

Sodium thiosulfate + hydrochloric acid  → sodium chloride + water + sulfur dioxide + sulfur

Sodium thiosulfate reacts with hydrochloric acid to produce sodium chloride, sulfur dioxide, sulfur and water. (Markedbyteachers.com. (2019))

ORIGINAL EXPERIMENT:

The methodology used has been adapted from 0.1m and 1.5m of HCI acid solution and added another 2 trials. More trials adds better accuracy onto the data. With higher concentrations of HCI acid to the thiosulfate solution more collisions result in a decrease in the rate of reaction time. The data collected will then lead to a closer average which will get the truest value.

RESEARCH QUESTION:

How does acid concentration affect the rate of reaction?

MODIFICATION TO METHODOLOGY:

To modify the original method of the experiment a larger number of trials were introduced, from 3 to 5 in order to ensure that the data is even more reliable. Trials are repetitions of the same procedure Trials are done for multiple reasons.(Study.com. (2019)).Firstly, trials are used to minimize the impacts of errors done in any one trial by averaging multiple trials together. Secondly, they are done to minimize random effects of uncontrolled variables by averaging multiple trials together. Thus, the more trials taken, the closer the average will get to the true value. (Study.com. (2019))

MANAGEMENT OF RISKS:

-          Don’t pour the sulfur dioxide down the drain because it is a piscicide. Instead, pour the end result of the experiment into a large beaker and give it to the supervisor.

-          Sulfur dioxide can cause irritation to the eyes and lungs, particularly to people with asthma to prevent this from happening, always wear goggles whilst doing an experiment and make sure the laboratory is well ventilated and avoid breathing directly over the top of the flask

-          Fumes are dangerous so be careful with the reaction. To prevent anything from happening, open the windows.

-          Liquids are corrosive so do not touch them. If liquid goes on hand then wash them thoroughly.

-          Experiment should be handled carefully and slowly.

RUN DATA:

 TRIAL TIMES (SECONDS) CONCENTRATION TRIAL 1 TRIAL 2 TRIAL 3 TRIAL 4 TRIAL 5 0.1m 9.99s 11.02 10.84 11.01 10.89 1.5m 7.10 7.13 6.65 6.56 6.63 3m 5.70 6.03 5.78 6.01 5.97

PROCESSING OF DATA:

 Calculation Example for 1 m Mean x̄= sum of all numbers/number of numbers T1→(+)T5 / 5 = 10.75 Uncertainty UNC= Largest-Smallest /2 = 0.515 % Uncertainty %= UNC/Average x 100 $\frac{0.515}{10.75}$ x 100 = 2.797
 CONCENTRATION x̄ UNC %UNC 0.1m 10.75 0.515 4.79% 1.5m 6.814 0.285 4.18% 3m 5.898 0.165 2.797%

TRENDS, PATTERNS & RELATIONSHIPS:

Graph 1 produced a straight line, The graph shown above  has a 92.2% positive correlation. When the concentration is high, the rate of reaction also becomes high hence, the line of best fit was very steep. The amount of concentration causing the atoms to gain more momentum within the beaker, the high concentration of hydrochloric acid within the beaker then create what is called a “collision affect” this is because there are more particles in the same amount of space, so they collide more often and therefore create activation energy. The time for the reaction to occur is a direct measure of the rate of the reaction. Therefore, the rate of the reaction between Na2S2O3 and HCl is directly proportional to the concentration of Na2S2O3 solution. The straight line is a trend line, modelled to come as close as possible to all the data points. The trend line has a positive slope, which shows a positive relationship between the rate of reaction time and HCI concentration levels. The points in the graph are closely assorted in between the trend line due to the strength of the relationship between time and concentration.

LIMITATIONS OF THE EVIDENCE AND RELIABILITY AND VALIDITY OF THE EXPERIMENTAL PROCESS:

 LIMITATIONS OF THE EVIDENCE Reliability and validity of the experiment Human errors- Determining when the ‘X’ was fully covered. Varying times for collecting the same reaction times indicates that the raw data for time is inconsistent and therefore, imprecise. Timekeeping was subjected to an individual’s personal interpretation. The stop watch could have been stopped a second after the ‘X’ had disappeared, causing outliers and pointless numbers within the work. In this manner, the experimental prepare is unreliable due to human Errors Chemical residue may have been left behind in the measuring cylinder and test tube. If the equipment had remnants of water from the last wash or was contaminated by not being washed out properly the last time it was used this contributes to the data being imprecise. Uncalculated and unwanted remnants of water particles and thiosulfate particles caused a faster reaction. Random errors such as this contributes to the experimental process being unreliable. Measurement estimation error- Adding the different concentrations of HCl and different beakers filled with thiosulfate could be slightly over or below the mark even if only by a very small amount If the beaker is filled above or below the desired amount it could cause a faster reaction. Therefore, the reaction rate data is inaccurate. By having faster reaction times than needed it adds more unrequired data numbers which could conclude to a higher amount of outliers thus, the Experimental process lacks validity due to a human error.

CONCLUSION:

In conclusion, the overall investigation of the concentration of HCl acid on the rate of reaction was successful. The graph is as predicted as the trend line has a positive slope, which shows a positive relationship between the rate of reaction time and HCI concentration levels, backing up the final results and the research question this is due to the fact that, the concentration affects the reaction rate, because of the Collision theory, by increasing the concentration of HCl acid, the faster the number of reacting molecules will vibrate, this means more collisions between atoms, ions or molecules within the beaker will occur, as a result the chemical reaction will be produced at a more rapid speed. The method used for the experiment also helped with the  reliability of the outcome this is related to the fact that, throughout all the trials, the same person observed the ‘X’ disappear, hence the same eye judgement was used for accuracy as well as the similarities of all 5 trials conducted the ‘X’ was kept the same. Another factor that helped with the precision of the experiment was that after each trial the beaker was washed and dried with a paper towel in order to get rid of any sulfur residue or water particle remnants. Doing so minimised a great deal of errors throughout the experiment and made it all reliable and exact. Therefore, it can be concluded that the concentration of sodium thiosulfate has an all-inclusive effect on the rate of reaction.

SUGGESTED IMPROVEMENTS AND EXTENSIONS

 Analysis of Evidence Suggested improvements and Extensions Use equipment that will give an accurate data results The moment the cross completely disappeared relies far too much on human judgement. This can be improved by using a spectrophotometer.  A spectrophotometer is an instrument that measures the intensity of light absorbed after it passes through a sample solution. With the spectrophotometer, the amount of a concentration known chemical substance can also be determined by measuring the intensity of light. (Chemistry LibreTexts. (2019) More trials to therefore add even more accuracy Experiments carried out from 5 to 15. Moreover comparing results with peers whose experiment which also took concentration as a changing variable this would help in verifying the experiments conclusion more accurately.

REFERENCES:

-          Opentextbc.ca. (2019). Factors that Affect the Rate of Reactions – Introductory Chemistry – 1st Canadian Edition. https://opentextbc.ca/introductorychemistry/chapter/factors-that-affect-the-rate-of-reactions-2/ [Accessed 24 Aug. 2019].

-          Chemistry LibreTexts. (2019). Factors That Affect Reaction Rates. https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Kinetics/Reaction_Rates/Factors_That_Affect_Reaction_Rates [Accessed 24 Aug. 2019].

-          Markedbyteachers.com. (2019). Sodium thiosulphate + hydrochloric acid → sodium chloride + water + sulphur + sulphur dioxide – GCSE Science – Marked by Teachers.com. http://www.markedbyteachers.com/gcse/science/sodium-thiosulphate-hydrochloric-acid-8594-sodium-chloride-water-sulphur-sulphur-dioxide.html [Accessed 24 Aug. 2019].

-          (Study.com. (2019)). https://study.com/academy/lesson/repeated-trials-definition-purpose.html [Accessed 24 Aug. 2019].

-          Study.com. (2019). Repeated Trials: Definition & Purpose – Video & Lesson Transcript | Study.com. https://study.com/academy/lesson/repeated-trials-definition-purpose.html [Accessed 24 Aug. 2019].

-          Chemistry LibreTexts. (2019). Spectrophotometry. https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Kinetics/Reaction_Rates/Experimental_Determination_of_Kinetcs/Spectrophotometry [Accessed 24 Aug. 2019].

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