Pressure - If the pressure is increased the particles in the gas are pushed closer. This increases the concentration and thus the rate of reaction.
Surface Area - If a solid is powdered then there is a greater surface area available for a reaction, compared to the same mass of unpowdered solid. Only particles on the surface of the solid will be able to undergo collisions with the particles in a solution or gas.
Method
To do this experiment you need 2 measuring cylinders, a Conical flask, a glass beaker and goggles.
Before doing this experiment you need to take some safety precautions:
- Keep your goggles on all the time.
- Keep all bags away from the table where you are going to do the experiments.
- All stools should be under the tables.
- The experiment should be done standing not sitting on your stools.
First you get the hydrochloric acid 0.1M in one measuring cylinder and also sodium litho sulphate in another measuring cylinder. The concentrations should be both the same amount, which is 10ml.Than put both concentrations into one conical flask. Just as you put the concentrations into the conical flask start the stopwatch. Place the conical flask on the centre of a cross and mix it. Mix it and stop the stopwatch when the cross is not visible anymore. Record your time of reaction.
Repeat the same procedure for the Rest of the reaction but using different hydrochloric acids each time. Use the following hydrochloric acid concentrations after your first reaction:
- Hydrochloric acid 0.25M
- Hydrochloric acid 0.50M
- Hydrochloric acid 0.75M
- Hydrochloric acid 1M
The Sodium litho sulphate stays the same for all the reactions.
The measurement that I will make is the time it takes the concentration to react or change to sulphur.
In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the Hydrochloric acid and Sodium thiosulphate will not be mixed up. The amount of Hydrochloric acid will be 10ml each time, and the amount of Sodium thiosulphate will be fixed at10ml. All of these precautions will make my final results more reliable and keep anomalies at a minimum so thus make the entire investigation more successful.
Scientific knowledge
Colloids are important in this experiment because the reaction between Sulphur and hydrochloric acid forms a 'colloid', which makes the solution go cloudy. When you use a higher concentration the amount of colloids colliding goes up which means that the rate of reaction is speeded up. Sulphur and hydrochloric acid however cannot mix; this triggers the two substances to turn cloudy. Every colloid has at least two parts; one part is the continuous phase like the water in milk or the air in mist. The other part is split up into minute particles like the fat in milk or the water droplets in mist. These scattered particles make up the disperse phase. Colloids make the light scatter causing the solution to turn cloudy, it does this when light rays pass through a colloid and are reflected or refracted every time it meets one of the droplets or particles in the solution. Therefore when the concentration of thiosulphate solution is increased the amount of particles colliding is increased.
Results
Conclusion
The pattern in my results is that it goes from high to low. The time it took for the hydrochloric acid 0.1M to react was 66 seconds, the time for the hydrochloric acid 0.50M to react was 42 seconds and the time for hydrochloric acid 1M was 31 seconds. So the lower the concentration the longer the time whereas the higher the concentration the shorter the time.
My prediction that I predicted was correct. This tells me and I have learnt that the rate of reaction depends on the mol of concentration used and it also tells me that different factors affect the rate of reaction like the temperature; in a cold reaction mixture the particles are moving quite slowly, the particles will collide with each other less often, with less energy, and less collisions will be successful. If we heat the reaction mixture the particles will move more quickly, the particles will collide with each other more often, with greater energy, many more collisions will be successful. The temperature in this experiment was at normal room temperature.
The amount of concentration used also affects its-In a reaction where one or both reactants are in low concentrations the particles are spread out and will collide with each other less often resulting in fewer successful collisions. In a reaction where one or both reactants are in high concentrations the particles are crowded close together and will collide with each other more often, resulting in an increased number of successful collisions.
The surface area affects the rate of reaction because large particles have a small surface area in relation to their volume- less particles are exposed and available for collisions. This means less collisions and slower reaction. Small particles have a large surface area in relation to their volume- more particles are exposed and available for collisions and a faster reaction. The catalysts also affect the rate of reaction. A catalyst is a substance, which increases the rate of chemical reaction, without being used up in the process. Catalysts are specific i.e. different reactions need different catalysts. Because catalysts are not used up, only small amounts are needed. Catalysts work by reducing the activation energy- the minimum energy needed for a reaction to happen.
Evaluation
My method was a good one because I explained every step and I included some safety precautions for a safe experiment. I can improve the method by including diagrams of each step.
My results were reliable and helpful and I can get better results if I done another two readings for each reaction or I can compare them to another person’s results. To get the
best results I could also work out the averages to find a more accurate reading.
