Factors Affecting the Rate of a Chemical Reaction: The Kinetics of a Thiosulfate Solution - Lab Report Example

Factors affecting the rate of a chemical reaction – The kinetics of a Thiosulfate Solution Introduction: Various approaches are used to study the kinetics of reactions. A usual procedure is to monitor some property, such as intensity of color due to a reactant or product, which changes during the course of a reaction. In the present experiment, the priority studied is the precipitation of a product, sulfur, which forms when solution of hydrochloric acid and Thiosulfate are mixed. When a solution of Thiosulfate is acidified, the following reaction takes place: S2O32- (aq) + 2H+ (aq)  H2O + SO2 (g) + S (s) On mixing a solution of acid, such as HCI, and a thiosulfate solution, there is an initial time-delay, then a precipitate of sulfur appears fairly sharply. The time interval between initial mixing and sulfur precipitation is a measure of the initial rate of reaction (i.e. the amount of time for a given amount of product, sulfur, to form). Recall that a rate for a chemical reaction is expressed as an amount of product formed (or reactant used up) divided by the time interval of the change:  concentration /  t Aim: The aim of my experiment is to determine the dependence of the initial rate of reaction on the initial concentration of thiosulfate ion. The concentration of the other reactant, H+, will be kept constant. Research question: How does the initial concentration of thiosulfate ions affect the rate of the reaction given constant concentration of H+ cataions? Hypothesis: A higher initial concentration of thiosulfate will lead to faster rate of reaction, since an increase in the number of thiosulfate ions per unit volume will lead to higher probability for successful collision. Variables: Dependent: Time (+/- 0.01s) Independent: Initial concentration of thiosulfate ions (+/- 1dm3) Controlled: Concentration of thiosulfate ions  1 mol/dm3 Concentration of hydrochloric acid  2 mol/dm3 Amount of hydrochloric acid added  5 mL (+/- 0.1 mL) Room temperature  constant at roughly 23oC (+/- 0.5oC) Temperature of solution  constant at room temperature Apparatus: Controlled: How to control them: Apparatus By using the same apparatus for each trial for each different amount of stock solution. Apparatus List: 1 piece of paper 1 pen 1 stopwatch ± 0.01 sec. graduate beaker 250dm3 ± 1dm3 1 graduate beaker 100dm3 ± 1dm3 1 pipette 10dm3 ± 0.1dm3 1 graduate beaker 50dm3 ± 0.5dm3 1 graduate beaker 300dm3 ± 1dm3 Chemicals: Water 240dm3 Solution of 1M of thiosulfate 80dm3 2M Hydrochloric acid 50dm3 Method: Effect of Thiosulfate Concentration on Reaction Rate (1) Prepare a piece of white paper with a large "X" marked on it (pen or pencil, make it dark). (2) A solution of 1 M sodium thiosulfate, is available (center bench or hood). Add 70 mL of this solution to 210 mL of water to make a solution approximately 0.25 M in thiosulfate. We will refer to this as your "stock thiosulfate solution". (3) Measure 50 mL of this stock thiosulfate solution into a 250 mL Erlenmeyer flask. (4) Carefully noting the time with a stopwatch or clock with a second hand, add 5 mL of 2 M HCI (provided for you by the stock room personnel or instructor). (5) Swirl the contents of the flask vigorously to mix, then place it on the white paper prepared in step (1). (6) Look down vertically through the flask. When the "X" disappears (due to the sulfur precipitate obstructing your vision), note the time. (7) The experiment is now repeated four more times, using progressively more dilute thiosulfate solutions. Note, however, that for each experiment, the disappearance of the "X" corresponds to formation of the same amount of precipitated sulfur in the reaction mixture. The diluted solutions are prepared as follows: Measurement # 2 40 mL stock thiosulfate solution diluted to 50 mL by adding water Measurement #3 30 mL stock thiosulfate solution diluted to 50 mL by adding water Measurement #4 20 mL stock thiosulfate solution diluted to 50 mL by adding water Measurement #5 10 mL stock thiosulfate solution diluted to 50 mL by adding water In each experiment, addition of 5 mL of 2 M HCI solution assures that the concentration of H+ does not vary. Only the initial concentration of thiosulfate varies. Raw data table: Time needed for a Stock solution diluted with water to 50dm3 to react with 2M HCl in seconds Trial 1 (+/- 0.01s) Trial 2 (+/- 0.01 s) Time needed for 50dm3 of stock solution to react with 2M HCl ± 0.01 19.59 21.10 Time needed for 40dm3 of stock solution diluted with 10dm3 of water to react with 2M HCl 29.08 30.35 Time needed for 30dm3 of stock solution diluted with 10dm3 of water to react with 2M HCl 41.65 42.69 Time needed for 20dm3 of stock solution diluted with 10dm3 of water to react with 2M HCl 63.81 68.03 Time needed for 10dm3 of stock solution diluted with 10dm3 of water to react with 2M HCl 134.63 146.13 Data Processing: The collected data indicates that the rate of reaction is increasing with increasing amounts of thiosulfate solution. An increase in the amount of thiosulfate augments the amount of particles available in solution to react. Hence there is a larger probability for reactants to react and so the rate of collisions increases which in turn increases the rate of reaction. Moreover as it is assumed that the total amount of sulfur created during the reaction remains constant, it can be implied that the usage of reactants during the reaction is small which supports the idea that the concentration of reactants is constant throughout the reaction. Given the two unique sets of data, the stock solution of thiosulfate was plotted against time required for reaction (that is when the X mark under the beaker disappears). Each plot represents one set of data along with the associated minimum and maximum slope lines in order to deal with the uncertainties involved. The plots are shown on the next page for reference. Uncertainties Based on the graphs below it can be determined that certain points lie beyond the error bars which indicates some uncertainties in the data taken. However the outlying points and the minimum and maximum slope lines lie close to each other which indicates that the data is healthy enough. Conclusion There are some sources of error in the data acquired which could possibly be due to: Errors in measurement of solution added for the X mark to disappear; Errors in time measurement of solution added for the X mark to disappear; The experiment could be further improved with smaller measurement intervals for the solution added; A better form of measurement should be used than the X mark disappearing such as using a source of light or measuring the pH. Read More