An investigation into the effect of concentration on the rate of reaction.

SURFCE AREA : increasing the surface area increases the exposed area for the chemical reaction and increasing the rate of reaction

PRESSURE : if one or more of the reactants are gases; an increase in pressure forces the particles to get closer causing more frequent collision thus increasing the rate of reaction

SCIENTIFIC KNOWLEDGE :

THE COLLISION THEORY:

Any reaction can only take place when the reacting particles collide together. Not all collisions are effective, the particles which collide with a minimum activation energy can undergo a successful collision and the reaction take place.

As the number of collisions increases per unit time, the rate of the reaction is faster.

So increasing the concentration of a reactant increases the number of particles available to react thus the number of successful collisions per unit time increases and the reaction goes faster (i.e. the rate of the reaction increases )

 

   

PREDICTION : 

I predict that as the solution becomes more concentrated the rate of the reaction will be faster. The independent factor ( concentration ) is directly proportional to the reaction rate. So the more concentrated the solution is the faster the reaction rate will be.

   

      ♦I am going to prepare the different concentrations of sodium thiosulphate solution from one reagent bottle containing the same solution (sodium thiosulphate conc. 0.30 mole ) and water to dilute. The following is the method;

1. using a measuring cylinder I will measure 50 cm3 of  the solution ( sodium thiosulphate ). Place it in the conical flask.
2. measure 40 cm3 of solution, add 10 cm3 of water to it then pour in the conical flask.
3. measure 30 cm3 of solution, add 20 cm3 of water to it, pour in the conical flask.
4. measure 20 cm3 of solution then add 30 cm3 of water to it then pour them in the conical flask.

5. measure 10 cm3 of solution add 40 cm3 of water to it then place in the conical flask.

Now I have the needed five concentrations for my experiment.

PROCEDURE :

1. add the first concentration of sodium this sulphate to the

                     conical flask.  

2. place the flask over the paper marked with X. look above the

                     flask.

3. add 5cm3 HCL solution using a pipette. Immediately start the

                    stopwatch .

4. A precipitate of sulphur (pale yellow ) will appear , deposits

                    at the bottom of the conical flask observing the cross        gradually  

5. when the cross is completely covered with the yellow

           precipitate stop the stopwatch and record the time taken for

           the cross to obscure .  

6. Repeat the experiment again using the different conc. Of

                    sodium thiosulphate and the same concentration and volume

                    of  hydrochloric acid .

THE DIAGRAM SHOWS THE SULPHUR PRECIPITATES IN MY EXPERIMENT :  

                        Conical flask  White paper

                                                                                                                                                                   

                                               

At the start of the reaction before the formation of sulphur.  

                                         

   After a while sulphur appears but does not obscure the cross completely.

 after the reaction is complete, the cross is no longer visible.

REPETITION OF THE EXPERIMENT :

        I have repeat my experiment using 5 concentrations at a time at last twice . for more accuracy and a trial to reduce the human error , I will repeat my experiment three times taking the average between them .    

SAFETY AND PRECAUTIONS :

1. handle the acid with care and responsibility because it is corrosive and might hurt the skin.
2. Make sure glass objects cannot roll off the tables and also make sure that they do not have cracks.
3. Do not smell the evolved gas while looking at the disappearing cross because it is harmful.
4. Do not hold the reacting conical flask during the reaction to avoid heat transfer.

RESOURSES :

 

My teacher’s text and Earl Wilford.  

II- OBTAINING EVIDENCE  

THE FOLLOWING TABLE SHOW THE RESULTS OF THE THREE EXPERIMENTS ( THREE REPEATS ) :

The following table shows all my work (procedure) including the averages of the above results :

III- ANALYSING EVIDENCE

The following graph show the time needed to obscure the cross in the First experiment :

     

Second experiment :

Third experiment :

This graph shows the average time to obscure the cross: (the three experiments )

The following show the rate of the reaction at each concentration with a line of best fit :

  The first three graphs (curves ) show great similarity, the three of them show that the time needed to obscure the cross is inversely proportional to the concentration of a solution meaning that as the concentration of the solution increases the time needed decreases.

   The graph containing the averages is also quite similar to the above three because the three results had near values due to the accuracy of my experiment. I noticed that the steepest is the beginning of the curve i think this is because at the beginning of the reaction id the fastest for the reactants are still not consumed.  

   The graph expressing the rate of the reaction  and its line of best fit show another relation it is between the concentration and the rate of the reaction the  relation is a positive one meaning that the rate of the reaction is directly proportional to the concentration of a solution.  

SCIENTIFIC EXPLANATION :

 As I have said before increasing the concentration increases the chance for successful collision per unit time thus increasing the rate of the reaction.

CONCLUSION :

 As the concentration of the solution increases the rate of the reaction increases.

My conclusion support my prediction  all what I had predicted happened. When the solution is more concentrated the time taken for the reaction to complete is less than that when the solution is less concentrated, and thus the rate of the reaction increase by the increase of the solution.

IV- EVALUATING EVIDENCE

      I think that my results and evidence are quite sufficient that if anyone else repeats my experiment should have a conclusion like mine. He should conclude that the more the concentrated the solution is, the faster the rate of the reaction is.    

   

   All the variables in my experiment are easy t control and possible to measure that I did not find any difficulty in controlling the variables.  

   I think that my results are quite reliable because it goes with my scientific knowledge and predictions.

  Some improvements such as the following could be applied to improve the accuracy of my procedure;

 - I might repeat the experiment one more time although three times are quite sufficient but my results would be more accurate if I do more repeats.

- I prepared the concentrations using a measuring cylinder but it would be more accurate if I use titration.

- I might improve the accuracy of my experiment by trying more in-between concentrations  to get a bigger range of results. A bigger range of results would improve the averages and will fill some gaps in the graphs.

further investigations that may elongate my own experiment are like:

 I may investigate the effect of other variables on the rate of the reaction e.g. temperature, catalyst, surface area or pressure.

 I may also use other reactants to observe the effect of concentration on the rate of reaction