Thursday, October 13, 2011

Rates of Reaction Experiment

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Rates of Reaction Experiment � Design Type


Introduction


In this experiment, Sodium Thiosulfate is reacted with Hydrochloric acid to study the affect of changing the concentration of one of the reactants, on the reaction rate. The products formed are Sodium Chloride, Water, Sulfur Dioxide and Sulfur.


NaSO(aq) + HCl(aq) = NaCl(aq) + HO + SO(aq) + S(s)


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As the precipitate of sulfur forms, it masks the cross-drawn on the filter paper and a time for the reaction to complete can be measured.


Hypothesis


As the concentration of one of the reactants in a reaction increases, reaction rate also increases.


Aim


To show the effect of concentration on rate of reaction.


Materials


M HCl(aq) x Burette Stand and clamp


0.5 M NaSO(aq) 10 mL measuring cylinder


Stop Watch x Burette


Sheet Of White Paper with a Cross (pencil) Conical Flask


Method


1. Placed 50mL of thiosulfate solution in the 50mL conical flask using the burette. Added 5mL of dilute HCl(aq) to the solution in the flask using the 10mL measuring cylinder, and at the same time started the stopwatch. Swirled the flask twice and placed it over the piece of paper with the mark on it.


. Looked vertically over the conical flask and timed the reaction by stopping the stopwatch when the cross was no longer visible.


. Rinsed the flask.


4. Repeated the experiment using 40, 0, 0 and 10mL of the thiosulfate solution made up each time to a volume of 50mL with distilled water, and still used 5mL of HCl(aq).


DIAGRAM


NB. A lab coat, safety glasses and gloves were worn during the experiment.


Results


Note Concentration of NaSO(aq) calculated before (50mL) adding to HCl (55mL).


Dilution of NaSO(aq)


Attempt 1 4 5


HO (mL) 0 10 0 0 40


NaSO(aq) (mL) 50 40 0 0 10


Concentration of NaSO(aq) (mol/L) 0.5 0. 0.15 0.1 0.05


Attempt 1 4 5


Concentration of NaSO(aq) (mol/L) 0.5 0.0 0.15 0.10 0.05


Concentration of HCl(aq) (mol/L) .00 .00 .00 .00 .00


Agitation (Swirls)


Time (s) 7.87 0.8 7. 5. 14.50


1/Time 0.0588 0.00 0.0687 0.01687 0.00745








The slope of the Concentration Vs. Time graph at two different points


m1=(y-y1)/(x-x1)


m1=(0.8-7.87)/(0.0-0.5)


m1=-48 (sf)


m=(y-y1)/(x-x1)


m=(14.5-5.)/(0.05-0.10)


m=-1.5 x 10 (sf)


The slope is steeper where the concentration of the thiosulfate solution is lower, as there are less particles in the solution for the HCl(aq) to react with to form S(s) therefore the solution requires a longer amount of time to react. The slope is shallower where the concentration is higher as there are more particles in the solution to react with HCl(aq) to form S(s) and therefore there is a higher chance of effective and frequent collisions between reactants, hence more products are formed and therefore the reaction time is shorter.


Analysis and Evaluation


The independent variable in this experiment was the Concentration of NaSO(aq).


The dependent variable in this experiment was time i.e. reaction rate.


The controlled variables in the experiment were atmospheric pressure, temperature, concentration of HCl(aq), the amount of agitation and the state of subdivision of the reactants.


The graph of Concentration of NaSO(aq) Vs. Time clearly indicates that as concentration is decreased, time for the reaction to occur increased.


The graph of the Reaction rate clearly indicates that as concentration increased, reaction rate also increased. Therefore from this experiment it is evident that reaction rate is directly proportional to the concentration of the reactants.


Random Errors


• If there are variations in eye level when taking the burette reading then the amount of thiosulfate solution will increase or decrease, and as a result the reaction rate will also increase or decrease.


• If there are variations in the ambient temperature or atmospheric pressure, then the amount of thiosulfate solution or hydrochloric acid will increase or decrease, and as a result the reaction rate will also increase or decrease.


Systematic Errors


• If the burettes and the measuring cylinder have been incorrectly calibrated by the manufacturer, then the amount of NaSO(aq) or HCl(aq) in the conical flask would have been higher or lower than required, thus the concentration of these two substances in the conical flask may have been affected, and consequently increased or decreased time.


• If a contaminated sample was used in the experiment, then the concentrations would have been affected, thus lengthening or shortening the times to react.


• The exact point where the cross disappears from sight is hard to gauge, therefore the time taken for the cross to disappear may not have been consistent.


• The amount of agitation may have varied with each attempt in the experiment.


Some improvements that could have been made to the design of the experiment to reduce errors are


• To do the experiment in a temperature controlled environment where the atmospheric temperature and pressure can be monitored for small increases or decreases and can then be rectified.


• Use a machine to agitate the solution to keep the agitation consistent.


• Repeat the experiment.


Conclusion


The Rate of reaction is directly proportional to the concentration of the reactants. As the concentration of NaSO(aq) increases, reaction rate increases.


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