E.g.
If we have a large cube only the surface would react with the particles. If we break up the large solid cube more surfaces would be created, so there would be more sodium thiosulphate in contact with the hydrochloric acid. Therefore the larger the surface area, the faster the reaction.
Particles can only react with the surface Same size cube split up into 4 pieces.
Of the cube. More particles in contact with the
Surface area of the cube.
Effect of Catalyst
Catalysts are chemicals, which speed up the rate of reactions. They remain uncharged the catalysts are very specific (only work on one type of reaction) and increase the rate of reaction. A catalyst works by giving the reacting particles a surface to stick to where they can collide into each other. This increase the number of collisions, therefore the chemical reaction happens quicker.
The Collision Theory
Reaction rates are explained by collision theory. All the substances are made up of particles. The particles might be atoms, molecules or ions. The rate of reaction depends on how often and how hard the reacting particles collide with each other. The particles have to collide for a reaction to take place. The particles have to collide hard or no reaction will happen, if the particles do not collide hard enough then the particles will just bounce off each other.
I have decided to investigate that does changing the concentration of sodium thiosulphate effect how quickly the reaction happens.
A more concentrated solution reacts more quickly. The hydrochloric acid particles can only react with the sodium thiosulphate particles when they collide. The particles of hydrochloric acid and sodium thiosulphate move randomly through the liquid. As you increase the concentration of the sodium thiosulphate there are more sodium thiosulphate particles in the same volume. Therefore there is greater chance of the sodium thiosulphate particles collide with the hydrochloric acid and reacting on the surface of the particles. This results in a reaction in a reaction happening in a shorter period of time.
“M” means “molar”. This is a measure of concentration. The 2M solution will contain twice as much acid particles compared to the 1M solution. If there were more acid particles in the same volume of solution than there would be more of a chance of a successful collision between the acid particles (hydrochloric acid) and sodium thiosulphate.
Prediction:
I predict the higher the concentration of sodium thiosulphate the quicker the chemical reaction between the hydrochloric acid and sodium thiosulphate would take place.
Preliminary
In order for me to find out if my chosen (ml) volume of sodium thiosulphate is correct, I did trail runs starting with my lowest concentration 40ml of sodium thiosulphate, 10ml of hydrochloric acid and 20ml of water, My total volume was 70ml. I then did a trail run for my highest concentration 60ml of sodium thiosulphate, 10ml of hydrochloric acid and no water (this was my highest concentration as I didn’t dilute the solution and I added the most ml’s of sodium thiosulphate in this experiment). I did these trail experiments to check if my range of concentration was suitable.
Trial Experiment Results Table
The symbol equation for the reaction that I am investigating is
From the results above I know that my chosen concentration is suitable as I have a suitable range. There is appropriate difference in the time taken for the highest concentration and lowest concentration. From my results I understand that as you increase the volume of sodium thiosulphate the reaction time takes a shorter time, when you decrease the volume of sodium thiosulphate the reaction time takes a longer time. However I am going to decrease my range from 10ml of sodium thiosulphate increase to 5ml sodium thiosulphate increase. I would do this because it will give me more readings to help me draw up a better conclusion. The beaker goes cloudy because a chemical reaction happens between the hydrochloric acid and sodium thiosulphate.
I will keep my experiment fair by taking 5 different readings and repeating each experiment 3 times and I will me more of an accurate answer as I will be able to spot any odd results which I could compare with my other readings. I will keep the same concentration of acid (0.15 M) and I would also keep the same volume of hydrochloric acid. I will keep the overall volume of the solution the same as well. I will do my experiment at room temperature; therefore the temperature will be kept the same. Hydrochloric acid and sodium thiosulphate are both irritant and can cause redness of the skin. For safety reasons I will wear goggles and transfer the chemicals using a pipette. To obtain my results I will need a number of equipment’s, below is a list of the equipment’s I will be using,
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3 different measuring cylinders. The reason I will be using three different measuring cylinders is because I will be measuring three different liquids. These liquids are hydrochloric acid, sodium thiosulphate and water. I am using three different measuring cylinders so no reaction happens before I put all the chemicals into the beaker. The measuring cylinder I will be using would be in ml.
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A pipette. I would use a pipette to transfer the chemicals for the bottle to the measuring cylinder. This will prevent any irritant, and my volume of liquid will be more accurate.
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A stop clock. I will use a stop clock to time the reaction; a stop clock will give me an accurate reading as it reads every 10th of a second.
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A beaker or conical flask. I would use this equipment to put all the chemicals and water in for the reaction to take place.
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A black dot. I would use a black dot so I can see when the reaction has taken place. I would know this because the liquid turns turbid therefore the black dot disappears and I know that the reaction as happened.
Method
I will measure the following liquids in individual measuring cylinders, 60ml of sodium thiosulphate and 10ml of hydrochloric acid. I will add the sodium thiosulphate and hydrochloric acid into a beaker over a black dot. I will start my stop clock the moment I add all the chemicals into the beaker. When I can no longer see the black dot I will stop the stop clock and record the time taken for the black dot to disappear. I will repeat this method for all my measurements and I will repeat each experiment three times.
The table below shows the volume of sodium thiosulphate, hydrochloric acid and water that I will use.
