rate of reaction

Concentration.

An increase concentration means an increase in the number of particles. Which consequently lead there being more collisions hence increasing the rate of which a reaction occurs.

In my experiment the main variable in my opinion be the concentration .So I have decided to investigate these two variables by using secondary data/stats.

Investigating further the concentration and its affects.

The reaction I am going to investigate is between bromine and methanoic acid with an acidic catalyst being used.

Br2  + HCOOH                 2Br-  +2H+ +co2

To measure the rate of reaction in this experiment the intensity of red brown bromines is recorded at certain intervals of time.

Looking at the table it is very easy to conclude that the concentration of the bromine solution decrease as the time increases. This would therefore suggest that rate of reaction is at its quickest at 0-1 seconds as there are more bronime particles at hence there being more collisions. So as the time increases the rate of reaction decreases.

I have drawn two tangents on the graph below to prove this.

The two tangents I will plot will be at x=100 seconds and x=450 seconds. From what I have learnt so far I am hoping that reaction rate will be faster at the point x=100 seconds.

Reaction rate at x=100                             reaction rate x=450

My theory was correct.

The experiment I will be doing is between HCL and sodium thio-sulphate with the concentration of HCL being the variable.

The equation will look like this:

Na2S2O35H2O (l) + HCl(aq)                         NaCl(aq)  + H2O(I)  + SO2 (aq) + S(s)

I shall be using 5 different concentrations of HCl acid they will be 0.2, 0.4, 0.6, 0.8 and 1.0(Molars). The concentration of sodium thioulsphate will remain the same. I have learnt so far that a change in concentration can lead to a change in the rate of reaction. The higher the concentration the higher the rate of reaction will be. When HCL and Sodium thiosulphate react they form a cloudy mixture. I shall be measuring the rate of reaction by timing how long it takes for the solution to become so murky that visible cross placed at the bottom of the solution is no longer visible

Prediction

I predict that the rate of reaction will be greatly increased by the effect of concentration because it will increase the frequency of collisions between the two reactants. As the concentration increases the particles will move quicker and therefore will cause more collisions. At the end of this experiment I should have collected valid evidence to support this theory.

• Conical flask
• Measuring cylinder 2
• Stop watch
• Hydrochloric acid and sodium thiosulphate
• White paper 1Pencil
• 5 beakers
• Solution Soduimthiosulphate
• Soulution of HCL
• Conical Flask
• Pippet

Method

The first thing I shall do is to clear the worktop and it’s surrounding so it minimises the risk of any one slipping or causing injury.

I shall the check what apparatus is needed and gather them and organise them in an appropriate manner and put them in the centre of the worktop so there are out of harms way.

I shall then check if all the apparatus are safe to use for example the conical flask is made out of glass so I may have to check if it is chipped or not as it may lead to some one getting hurt.

Wear goggles.

On a piece of paper I shall draw a circle. In that circle I will draw two lines making an x shape. The two lines drawn in the circle shall have a diameter of 4cm

        

Shall then place the conical flask onto the piece of paper marked with an x.

Using a pipit and a measuring cylinder I shall measure 10 ml of HCL 0.2(variable) molar solution and pour it into the conical flask

I shall get my assistant to be get ready the stop clock and make sure it is working.

Using a different pipit and measuring cylinder I shall measure 10ml of soduimthiosulphate solution and the insert in to the conical flask. As soon as it has been inserted the stopwatch shall be started. Once the cross is completely disappeared and is not visible to my assistant the stopwatch will be stopped and the result shall be recorded.

 i Shall wash all the conical flasks, measuring cylinder and pipits.

I shall repeat the experiment and again however I will change the concentration of HCL.

Additional: clean any spills

Fair test.

The first things I have to take into account are the variables. The temperature of the room I was conducting my experiment in would always have to be constant as a change in room temperature could mean a change in the rate of reaction.

The concentration of sodium thiosulphate had to be kept the same as I was testing how an increase in the concentration Of HCl would affect the rate of reaction. If I were to increase the concentration of sodiumthiolsulphate than the experiment would be deemed inconsistent with the method.

The cross I would be using to see how long it takes for the solution to disappear would have to be the same size throughout the experiment. For example if I were to use a small cross when the concentration HCl 0.2 M and then use a large cross when the concetration of HCl Is 0.4M the experment would again be deemed inconstant as it the larger cross will take longer to disappear.

Also after taking down results I shall I have to wash the conical flask pipet and measuring cylinder before I take the results of the next experiment when varying the concentration of hcl because if I don’t then some part of the old solution may be mixed with the new experiment which could hamper the results.

It is also important that I shall keep the amount of solution the same, which is 20 ml, 10ml of HCL and 10ml of sodiumthiosulphate. If I were to be inconsistent with this and for example have 12ml of HCL and 10 ml of sodiumthiosulphate there would be an inconstancy with the results there would be more particles hence there would be more collisions. More collision would lead to increase in the rate of reaction.

Safety

While conducting the experiments I shall wear goggles prevent any harm if the solution of HCL or sodiumthiosulpahte got in my eyes. I shall also check all my apparatus are safe especially thing made out of glass such as the conical flask. Experiment shall be carried in a scientific laboratory with suitable worktops and large enough space to conduct experiment preventing injury or accidents. Place of experiment shall be carried out in an area where there are few people moving about preventing injury.

Prelimanry results.

Before doing a my final experiment I decided to a preliminary test so I could learn of any flaws and iron them out before the final experiment takes place.

After obtaining these results I decided to put them in a graph to find out how concentration affects the reaction rate. This graph is similar to the one I analyses in my research, which involved reaction rate of Bromine. So using that research as a base I would hope to see these set of results produce a smooth curve.

Looking at the graph I have been able to produce a smooth curve, which shows that as the concentration increases the reaction rate increases. This runs conjunctly with my prediction.

Improvements I would like to make. While doing this experiment I noticed that I was conducting it next to window. This in my opinion affected the results as the sun was shining continuously on the conical flask during the experiment, which could have led a rise in temperature. This in effect is likely to have increased the rate of reaction.

So next time I will conduct the experiment in an area, which will minimise the possibility of the sun affecting results.

Also while conducting the experiment I found that there was not much room and it was unsafe. I think this was due to four people working on one experiments. So when doing my final experiment I shall work with only one person. This would in effect decrease the chance of any hazards and make the conducting of the experiment quicker and much more efficient.

I have also thought about obtaining more than just two pairs of results. I think that taking 3 sets of results for each concentration would prove beneficial, as it will help me gain more accurate results for each concentration when taking the average.

Final Experiment/results

For this experiment I shall produce two graphs. One showing how long it takes for the cross to disappear and one showing the reaction rate.

I shall find the reaction rate by dividing one by the average number seconds taken for the cross to dissapear.

This graph below shows the reaction rate for each concentration.

It is again possible to see in this graph that the when the concentration is high the reaction rate is quicker hence making my prediction correct.  This can conclude that when the concentration of HCL was increase the amount of time it took for the solution to get cloudy when mixed with sodium thiosulphate became quicker.

Conclusion

After completing the experiment I can know come to some conclusion.

I very strongly believe that I was correct in my prediction that the rate of reaction will increase as the concentration of hydrochloric acid increases. I learnt that with a higher a concentration there would be more molecules in the combined solution with sodium thiosulpahte leading to more collisions. My prediction was proven correct when I stated that the as the concentration was increased the reaction rate was faster; this is shown in the graphs. You can also see this on the graph above as it clearly shows that as the concentration increases the rate of reaction increases. All my prediction were correct and all the research theories that had been stated did play some effect in the experiment.

Evaluation.

I believe that my experiment went according to plan as it was well planned and lots of research had been put in to it leading to the best results possible. Looking at the results I was pleased to gain results, which were predicted and expected. I knew what to expect as my preliminary experiment went well. One can see from the preliminary graph as well as final practical graph that they are both similar and have almost the same negative gradient.

I tried to gain my results in the most accurate possible. One must keep in mind that my experiment was carried out in a secondary high school so not all the latest and most expensive technologies were available for me to get the most accurate results. However considering the facilities available my results show that my measurements were correct.

There still could have been some ways in which I could have improved my experiment. For example one could have used digital stopwatch instead of an analogue watch to take time readings as this would have been much more accurate and convenient.

I tried to make the practical/experiment as fair as possible taking into account all the variables. I knew that my main problem would be the temperature, as I did not have much control over it. However the lab assistant tried to keep the room at room temperature, which was constant. I did try to complete the experiment as quickly as possible without rushing things and being too hasty so if there were going to be any changes in temperature I would minimise the effect of it.

Most other variables such as concentration were also not in my control as the lab technician prepared them. There could have been faults with the experiment however my results state other wise.

 

Cambridge foundation chemistry module 1