Increasing the temperature of a chemical transfers energy to it. This energy gives kinetic energy to the particles. So heating a chemical results in its particles moving faster. When particles are moving faster they collide more often and because they have more energy, it is more likely that the collision will lead to a reaction. Temperature affects my investigation because it will vary the rate of reaction. To ensure the investigation is fair the temperature must remain the same.
If a dilute solution of acid reacts with marble, the particles of the acid must move through a collection of many particles of water. If the solution is more concentrated, but the volume remains the same, then there are more particles of acid moving through fewer particles of water. This means that there is more chance of some acid particles colliding with particles of marble in a concentrated solution.
Many of the particles have reacted and changed after a while. The concentration of the original particles has decreased. There is less chance of a successful collision so the rate of the reaction slows down.
Concentration affects my investigation because it will vary the rate of reaction. To ensure the investigation is fair the different concentrations must be measured accurately.
The particles in a solid cannot react until the particles at the surface have reacted and moved away. If an acid was to react with a chunk of chalk and the chalk is in a solid ice cube, there are six sides for the acid particles to attack. If the cube of chalk is broken up into many smaller cubes, the particles on the surfaces of the small cubes that were inside the large cube are now open to attack. We have increased the area of exposed surfaces. The bigger surface area is made up of many more particles so there is now more chance of collisions taking place.
Surface area does not affect my investigation because both reactants are liquid.
Catalysts speed up (or slow down) reactions. If they increase the rate of reaction, time is saved. A catalyst often provides a surface where the particles can meet to react. Reactions on these surfaces need less energy transferred to make a collision successful. This will not affect my investigation because a catalyst is not used.
Hypothesis
The higher the concentration the faster the reaction.
Preliminary Work
I tested how long it would take for Sodium Thiosulphate to react with Hydrochloric Acid. Different concentrations were used such as 100%, 80%, 60% and 40%. 20% was not used because it took over 20 minutes and the reaction still hadn’t finished. If I were to change the experiment in any way, I would measure the solutions more accurately so the concentrations are correct therefore the experiment is fair.
This is the range of concentrations I used and the results:
Plan
Equipment –
Conical flask
Tile
Marker pen
Measuring cylinder
Beaker
Stop clock
The same person will monitor the reactions taking place.
We will be using 100%, 80%, 60% and 40%.
First we will place a marked tile on the table and put the conical flask on top. The concentrations will be measured out and poured into the conical flask. As soon as that has been done, we will start the stop clock. One person will monitor the solution, when the mark can no longer be seen through the solution the stop clock will be stopped and the results recorded.
The same procedure will be repeated with all the concentrations.
To ensure this procedure is safe goggles will be worn to protect our eyes from the chemicals and hair will be tied back.
Results
Analysis and Conclusion
The graph shows: as concentration increases, time decreases. This graph also shows that the relationship between concentration and time is good. There is a positive correlation.
The rate of change will not always be the same. Most chemical reactions are different to each other.
The gradient of my graph is 0.8.
Evaluation
My method is not too clear because the practical was done on two different occasions and the temperatures on these two days were different. This makes the experiment slightly unfair.
It was quite hard to tell when the reaction had finished because my sight is not perfect. To know exactly when the reaction has finished, a data logger could be attached to the experiment. A data logger robotically monitors the solution and gives exact times. It is more precise than a human eye, as a result making the results very accurate.
