will be successful.
Reaction rate is slow!!! Reaction rate is faster!!!
2) Size of solid particles (or Surface Area) increases collisions.
If one of the reactants is a solid then breaking it up into smaller pieces will increase its surface area. This means the particles around it in the solution will have more area to work on so there’ll be more useful collisions.
Large particles have a small Small particles have a large surface
Surface area in relation to their area in relation to their volume
volume less particles are exposed more particles are exposed and
and available for collisions. This available for collisions. This means
means less collisions and a slower more collisions and a faster
reaction. reaction.
Reaction Rate is slow!!! Reaction Rate is faster!!!
3) Concentration (or Pressure) increases the number of collisions.
If the solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules, which makes collisions between the important particles more likely. In a gas, increasing the pressure means the molecules are more squashed up together so there are going to be more collisions.
In a reaction where one or both In a reaction where one or both
reactants are in low concentrations reactants are in high concentrations
the particles are spread out and will the particles are crowded close
collide with each other less often together and will collide with each
resulting in fewer successful other more often, resulting in an
collisions. Increased number of successful
collisions.
Reaction Rate is slow!!! Reaction Rate is Faster!!!
4) Catalyst increases the number of collisions:
A Catalyst is a substance, which increases the rate of a chemical reaction, without being used up in the process. Catalysts are specific, different reactions need different catalysts. Catalysts are not used up, only small amounts of catalysts are needed. Catalysts work by reducing the Activation Energy, the minimum energy needed for a reaction to happen.
Since catalysts lower the amount of energy needed for successful collisions will be successful and the reaction will be faster. Also they provide a surface for the molecules to attach to therefore increasing their chances of bumping into each other.
I have chosen to investigate the effect concentration has on a reaction. This is because it is the most practical to investigate, it will take longer to prepare a solid in powdered and empowered form, and it is difficult to gauge a reaction changing the pressure, and if a substance is added to give the gas colour, it may influence the outcome of the experiment. Similarly the use of a catalyst complicates things, and if used incorrectly could alter the outcome of the experiment.
Both the Sodium ThioSulphate and the Hydrochloric Acid are soluble in water, so the concentration of either can be changed. I have chosen to vary the Hydrochloric Acid as it is available in larger amounts, and various concentrations are prepared.
Hypothesis:
My prediction is that when I add Hydrochloric acid to the conical flask with Sodium ThioSulphate in, a reaction should take place. I also predict that if there is higher concentration of Hydrochloric acid the reaction will be much faster than reacting with a lower concentration of Hydrochloric acid. From the collision theories I have gained enough information that the concentration will affect the rate of reaction.
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.
My final prediction is when you increase the concentration the quicker the reaction will be therefore making the cross disappear more rapidly.
Fair Test:
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 X as 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 and Sodium ThioSulphate will be 10cm3 each time. The temperature will also be the same throughout the experiment hopefully. All of these precautions will make my final results more reliable and keep anomalies at a minimum so therefore making the entire investigation more successful.
Apparatus:
In my experiment the following apparatus will be used:
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2 measuring cylinders (10cm3) – to measure the amount of Hydrochloric acid and Sodium ThioSulphate.
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1 Conical Flask (100cm3) – to put the Sodium ThioSulphate in, followed by the Hydrochloric acid. It will also be used to see the cross disappear and the rate of reaction.
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1 Stopwatch - to time the cross to disappear.
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1 piece of paper with an X drawn on it – to help to see the rate of reaction.
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1 pair of tongs – to carry chemicals.
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1 pair of goggles – goggles are needed for safety to the eyes.
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1 apron – worn to protect skin and clothing.
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2 pipettes – to put drops of substances in the conical flask.
The substances used in the investigation will be:
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Sodium ThioSulphate – used to react on the Hydrochloric acid.
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Hydrochloric acid (0.2 – 1.2%) – different concentrations to see rate of reaction (cross disappear).
Method:
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Firstly I will collect 10cm3 of Hydrochloric acid at a fixed concentration of 0.2M.
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Then I will collect 10cm3 of Sodium ThioSulphate at varying concentrations 0.2 – 1.2M.
- They will be put into different measuring cylinders using pipettes.
- I will then collect a conical flask and put it on top of a piece of paper with a cross-marked on it.
- The Sodium ThioSulphate will now be poured into the conical flask.
- The Hydrochloric acid will now be poured as well.
- Immediately the stopwatch will now be activated.
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When the mixture has sufficiently turned cloudy so that the letter X can no longer been seen.
- The stopwatch will immediately be stopped.
- The time will now be recorded.
The experiment will then be repeated with all the concentrations. The entire procedure will be repeated for improved accuracy in results.
The repeat results and averages will be taken to improve the credibility of the findings, present solid grounding for the final conclusion. The repeat results will help to eliminate any anomalies and the average will give a good summary of the results of the experiment. However if one set of results is entirely different to the other, a third experiment will be performed to replace the anomalous set of results.
Preliminary Results:
Final Results:
These are my final results; the tables show that my predictions were correct. The higher concentration in Hydrochloric acid will depend on how quickly the rate of reaction takes place.
Analysis:
I have analysed that the more concentrated a reactant is the quicker the rate of reaction time will be.
I have come to a conclusion because of several reasons. Firstly, my results give conclusive evidence that as concentrations of Hydrochloric acid decreases the longer it takes for the cross to disappear.
My results support my prediction without a doubt this is because I stated ’the greater the concentration of Hydrochloric acid the faster the rate of reaction. I assume I was correct because a secondary source states that the reaction time will be faster with a more concentrated solution because the more molecules there are thereby the frequency of successful collisions is greater and the reaction rate is speeded up.
Evaluation:
The overall investigation was a success as the method produced sufficient evidence to come to a firm conclusion, as it was suitable for the given task. The experiment went according to my plan despite some minor problems. For example I only obtained three sets of results and then calculated an average. I should have done more tests to provide myself with a better average.
I believe there is an human error factor involved in this experiment like when measuring liquids and looking for an end point in the reaction although the reaction I chose was fairly definite end point it was still difficult to tell whether the whole cross had disappeared or not. Instead of using a cross I could of used a light beam and when the light beam goes out that is an end point. An enhanced standard of measuring cylinders also could have been a major improvement. A glass pipette should have been used because they’re hand made much more accurate.
The equipment used was rinsed with tap water, which contains many impurities, which may have contaminated or changed the concentration of the substances. Distilled water could have been used as it is pure and has no impurities.
