The aim of the experiment is to investigate the factors affecting the rate of reaction between sodium thioslphate and hydrochloride acid, and why it affects the rate of reaction.
The collision theory
As we know all substances are made up of particle. Before we can get a chemical reaction, particles must crash together. They must collide with certain minimum energy, called the active energy. This is called the collision theory.
The more collisions between particles in a given time, the faster the reaction.
PREDICTION
I predict that as the temperature is increased the rate of reaction will increase.
When the temperature is increased the particles will have more energy and thus move faster. Therefore they will collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier to reaction and thus react successfully. If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur.
IDENTITY
Controlled Variables
- Concentration.
- Pressure.
- Surface Area.
-10 ml thiosulphate
-5 cm3 Hydrochloric acid
- Independent variables
-Temperature
- Dependant Variables
3) Uncontrolled Variables
- Room humidity
- Room temperature
1.the affect of temperature:
Raising the temperature makes particles collide more often time, and makes it more likely that collisions result in a reaction. Therefore as we increase the temperature, we increase the rate of reaction.
2. The effect of surface area:
If a solid is powdered then there is a greater surface area available for a reaction, compared to the same mass of empowered solid. Only particles on the surface of the solid will be able to undergo collisions with the particles in a solution or gas. For example if we are frying two pans of chips. One has potato cut into small, thin chips and the other pan has bigger, thicker chips. For the same mass of potato, small chips have a larger surface area than bigger chips. As we increase the surface area, we increase the rate of reaction.
3.The affect of catalyst:
A catalyst works by providing an alternative reaction pathway that has lower activation energy. Because a catalyst provides a reaction route of lower activation energy, however, a greater proportion of particles will have energy greater than the activation energy.
4.The affect of concentration:
If the concentration of a solution is increased there are more reactant particles per unit volume. This increases the probability of reactant particles colliding with each other.
5.The affect of pressure:
If the pressure is increased the particles in the gas are pushed closer. This increases the concentration and thus the rate of reaction.
SAFETY
In my experiment I will try carry out everything as safely as possible. This will include:
Not running - There will be people walking around with chemicals and hot liquids and glassware. You could fall and hurt yourself or others. You could run
Into or knock someone carrying hot materials or chemicals and as a result they could end up spilling them on you or themselves.
Wipe up spills - If you spill something it must be cleaned up quickly and appropriately. Someone could slip on chemicals that had been spilled on the floor and hurt themselves.
Wear goggles - You must wear goggles at all times when heating chemicals in case they spit or splash out of the test tubes. They may get into your eyes and blind you.
Acids are corrosive - This is basically the same as wiping up spills but this also involves carrying and handling the chemicals. Be careful not to get it onto your skin.
Report breakages - You must tell the teacher if you break any apparatus including glassware. Someone may not notice it and cut themselves on it.
Use tongs when carrying hot glassware - Tongs must be used or else you burn yourself and/or drop some apparatus containing chemicals.
EQUIPMENT
1 thermometer
1 beaker
2 measuring cylinders
1 conical flask
1 tripod
1 gauze
1 heatproof mat
1 stopwatch
1 Bunsen burner
Pad (marked with black cross) white cross
1 pair of tongs
1 pair of goggles
1 apron
2 Pipette
Sodium Thiosuphlate
Hydrochloric acid
Method
- Measure 5ml of 0.5M Hydrochloric Acid using the 10ml-measuring cylinder.
- Measure 10ml of Sodium Thiosulphate using the 50ml-measuring cylinder.
- Measure 40ml of water using the 100 ml measuring cylinder.
- Add the 35ml of water to the 15ml of Sodium Thiosulphate in the 150ml conical flask and take the temperature.
- Place a peace of paper with an X written on it under the 150ml conical flask.
- After recording the Temperature add the Hydrochloric Acid to the Sodium Thiosulphate, at the same time start the stopwatch.
- Look at the cross and keep looking at it.
- When the X is gone stop the stopwatch.
- Record time taken for the X to disappear and the temperature at the end.
- Repeat steps 1-9 with the selected different temperatures.
Diagram of our test
- When sodium thiosulphate reacts with an acid, a yellow precipitate of sulphur is formed.
Mix ➔ ongoing➔ Watch stopped
- Sodium Thiosulphate + hydrochloric acid ==> sodium chloride + sulphur dioxide + water + sulphur
-
Na2S2O3(aq) + 2HCl(aq) ==> 2NaCl(aq) + SO2 (aq) + H2O(l) + S(s)
Fair Testing
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 HCl and Thiosulphate will not be mixed up. The amount of HCl will be 5 cm3 each time, and the amount of thiosulphate will be fixed at 10 ml. I will not stir the chemicals at all and I will try to move them around as little as possible. This is to prevent any unwanted collisions, which may inadvertently speed up the rate of reaction. I will record the temperature of the liquids at the start and end of each experiment to find an average temperature for that particular experiment and so I can see any faults in the temperature of the liquids. One of the main aspects of my fair testing will be that I repeat my experiment for each temperature three times. I will do this so that I can obtain an average and also so that I can repeat any experiments further if they do not seem to fit in with the rest of my results.
These are my Preliminary Results:
From these Results we will keep the Volume of Thiosulphate 10 ml, Volume of Hcl 5 cm3 and the volume of water 40 ml.
These are my actual results; I have experimented 6 different temperatures with the same volumes (I have written them above) and I have repeated them 3 times to get an accurate result.
These are my results:
These are my Second repeated results:
These are my Third repeated results:
ANALYSIS
From this experiment I have found that as the temperature and concentration is increased the time taken for the reaction to take place decreases. This means the rate of reaction increasers as it takes less time for a reaction to take place, so more take place per second. In the temperature experiment the time taken for a reaction to take place decreased.
EVALUATION
I believe that I do have an accurate set of results and that I do have enough results to be sure about my conclusion. My results are accurate because when I read the collision theory it told me exactly what my results told me. I do not have any anomalous results, which do not fit in the pattern because my predictions coordinated with my results very well.
My method of carrying out my experiment was fairly accurate. I made sure that I washed the beakers clean for the other two concentrations and the second experiment, I measured the same amount of solution in each time and I stopped the stopwatch as soon as I thought the cross had disappeared but because it was based on our judgement it could be wrong, cause no scientific experiment is based on judgement. An improvement that we could have made would be that we would be able to carried out the experiment in a completely controlled environment, results would have been totally accurate.
All in all I think this was a good experiment and the best that could have been done with the time and resources available. The results supported my predictions and they seem to be fairly reliable results.
