How higher or lower concentration and temperature affects rates of reactions

The equation of the whole reaction: 

Sodium Thiosulphate + Hydrochloric Acid→Sodium Chloride + Sulphur + Sulphur Dioxide + Water

Na2S2O3(aq)+2HCL(aq)→ 2NaCl(aq)+S(s)+SO2(g)+H2O(g)

Hypothesis;

We assume that, by increasing the concentration of the substance, increases the rate of reaction because the higher the concentration is of the reactant, there is a greater chance of collisions to occur. In some cases, increasing the concentration of one of the reactants may have slight effect on the rate, but if you double the concentration of one of the reactants, it will double the rate of the reaction, meaning that they’re in proportion to each other.
We do also believe that temperature will increase the chances of the reactants to bump into each other and produce a collision. It’s because heat gives the reactant particles energy and by increasing the temperature the more energy the reactants get and therefore they will move faster, which alerts the rate of a reaction. Generally we presume that activation energy is a good factor of increasing the rate of a reaction because any extra energy provides a better chance of collisions.
In order for any reaction to happen, the particles must start colliding. This is true whether both particles are in solution, or whether one is in solution and the other one is a solid. If the concentration is higher, the chances of collision are greater.

Materials;

• Conical flask
• Blank white paper
• Marking pen
• Measuring glass
• Solutions with different

concentrations of Sodium Thiosulphate

• Hydrochloric acid
• Distilled water
• Stop Watch
• Flea
• Magnetic stick to attach with flea
• Magnetic Stirrer
• Thermometer
• Test tube
• Water bath
• Refrigerator

Safety Precaution;

If you spill acid on your skin it can become irritating, do not have something in the way that makes you uncomfortable while doing the experiment. Also, wear a lab coat and goggles to keep your clothes and eyes safe.

Method, Changing Concentration;

1. Start off by cleaning the materials with distilled water and wipe off the excess water.
2. Pour the volume of Hydrochloric acid and Sodium Thiosulphate stated in the table below into two measuring cylinders.
3. Mark the letter X on a blank white paper.
4. Place the X-marked paper on a magnetic stirrer.
5. Place an empty conical flask with a flea inside on the magnetic stirrer.
6. Pour the two liquids into the conical flask and turn on the magnetic stirrer.
7. Start the stopwatch when the two substances are poured into the conical flask. Let the stopwatch run until the mixture has turned sufficiently cloudy. When the letter X can no longer be seen stop the stopwatch.
8. Record the time on the results table.
9. Repeat the experiment 5 more times with all the concentrations stated in the table (according to the “trial”) below, follow the template, see table 1.

Remember to add extra distilled water to the remaining runs to keep the same volume

Method, Changing Temperature;

1. Start off by cleaning the materials with distilled water and wipe off the excess water.
2. Mark the letter X on a blank white paper.
3. Place the X-marked paper on a magnetic stirrer.
4. Pour 10ml of Sodium thiosulphate into measuring cylinders, for accurate measurements.
5. Place an empty conical flask with a flea inside on the magnetic stirrer, and add the liquid into conical flask from the measuring cylinder
6. Add 10 ml of Hydrochloric acid into a measuring cylinder, a new measuring cylinder to avoid contamination.
7. Pour the 10 ml of HCl into a test tube and increase/decrease the temperature according to “table 2” by putting the test tube into the water bath or refrigerator, measure the temperature with a thermometer.
8. When desired temperature is obtained, quickly pour the HCl into the conical flask. At the same time turn on the stopwatch and the magnetic stirrer. To get more accurate results be consistent with the spinning strength of the magnetic stirrer.
9. Stop the stopwatch when the cross is no longer visible and record the time onto the results table.
10. Wash the conical flask with distilled water.
11. Repeat the steps 4-10 three more keeping the same temperature.
12. Find the average of the two results.
13. Repeat 4-11, keep changing the temperature according to the template, see table 2.

Results;

Calculating moles of different concentrations:

Volume of HCL acid (cm3) * Original concentration (M) / Total volume (10 cm3)

1st – 3rd trial                →  10 * 1 / 10 = 1 mole

4th – 6th trial                →  7.5 * 1 / 10 = 0.75 mole

7th – 9th trial                →  5 * 1 / 10 = 0.5 mole

10th – 12th trial        →  2.5 * 1 / 10 = 0.25 mole

Conclusion;

The results do support our hypothesis about the concentration. When looking at the final results of the concentration, it shows that the higher the concentration of hydrochloric acid is, the faster the rate of the reaction. This is shown in the diagram when looking at the result in the 1st - 3rd concentration, it shows a concentration of 1 M and a rate of a reaction at 1.20, this results a faster rate of reaction than in the other concentrations in the trials which supports our hypothesis.

 

The results about the concentration do also show that the background information is true; according to the background information if the concentration is doubled so is the rate of reaction, and the result did show this. Between 0.5 and 1.0 M the amount of time almost halves as the concentration is doubled when looking at our results. We believe that the end results would show the concentration of the hydrochloric acid and the rate of reaction in proportional if our results had been more precise.

 

(Write about the graph of the concentration, when the graph is done!!)

 

The results do also support our hypothesis about the temperature, because when looking at the final results of the temperature it shows that the higher temperature is, the faster the rate of the reaction. From the knowledge we know about the background information about the temperatures effect on rates of reaction it states that heat gives the reactant particles energy and by increasing the temperature the more energy the reactants get and therefore they will move faster, which alerts the rate of a reaction. Therefore we can draw a conclusion that the results we have got do support our hypothesis and the background information because of these facts.  

For example, when looking at our result it shows that the amount of time for the reactant to react in trial 1 is much longer than for the reactants to react in the result on trial 12. This is because the temperature was increased from 15oC (test 1) to 40oC (test 3) and therefore the amount of time was also decreased from 02.03 minutes (trial 1) to 47.9 seconds (trial 12).

 

(Write about the graph of the temperature, when the graph is done!!)

 

The magnetic flea did also help the reaction rate because it produced more collisions when stirring the liquid because then the particles in the substance moves a lot and gets a better chance to bump into each other than if there were no stirring at all.  

Evaluation;

The experiment was well performed, even if it could have been done better. Results of trials vary slightly from one another, and this may be because different people were observing different trials. It was quite a personal view, to see when the reaction finished as it was determined when the X on the paper no longer was visible. It is possible that members of the group has an eyesight that may differ, by that it is meant even if the cross is not there it is seen by me but not my partner. The easiest way to improve this is having the same group-member to observe every trial to see when the reactants have fully reacted, which gives us more accurate results.  

Generally the lab was relatively accurate since everything that could have been done to get accurate results was done. Except the part when the method wanted the group members to determine when the reaction was completed between HCL and Sodium thiosulfate, this part was not accurate at all. The method is using bare eyesight to determine when the “cross” has disappeared, which in all sense is a very inaccurate way to determine when the reaction is complete. Because it’s difficult to see when all the “smog” that is created during the reaction has completely concealed the cross, after doing this for along period of time this could result in tired eyes which would give unpredictable results. But other things such as cleaning the equipment, drying the equipment properly after and measuring volume with a precise measuring cylinder went good.

 

The solution to avoid a problem like observing the disappearance of the X with your own eye is that a gas syringe could be used to collect the gas produced from the reaction which in this case is sulphur dioxide (SO2). This would be a better method instead of using a subjective approach to detect the disappearance of the letter X. To use this method a preliminary test should be done and measure the total amount of SO2 produced in the amount of chemicals used. Let the reaction take place for about 25 minutes, to be sure that the maximum amount of gas has been produced by this chemical reaction. So, when performing the real investigation, one could measure the rate of reaction by writing down the amount of time for the Hydrochloric acid and Sodium thiosulphate to produce the total amount of gas.

Another improvement could be that you do one more trial for each temperature chosen. This could give a better vision of how much the rate of reaction increases or decreases from the different temperature rather than knowing that it just increases/decreases.

To avoid contaminating the substances used during the lab, one member of the group had to clean all equipments used, properly and thoroughly. When cleaning, distilled water and normal tap water was used, distilled water was only used on the equipment in a lot of contact with chemicals. If the equipments are not cleaned properly or not cleaned at all there could be some chemicals or residue left on the equipments. Then the substances used during the lab would later be contaminated if dirty equipments are used, this would thereby lead to inaccurate results. By cleaning all equipments used during the investigation the factor of getting inaccurate results due to contamination was cleared. After cleaning the equipments it was made sure that no water was left since this could lead to contamination as the water could interfere with the substances used during the investigation, this was resolved by wiping the water with a peace of cloth.

 

Overall we are pleased with the results and the way the experiment was carried out. The results were fairly accurate because we repeated it three times and then took the average, and the results did prove our hypothesis as well. To make this experiment more interesting we would like to also investigate other factors which affect the rate of a reaction, for example using a catalyst and also to have a bigger/smaller surface area to see how they affect the rate of a reaction as well as getting a fully understandable knowledge of which of the factors does affect the rate of a reaction the most and why.