Although the particles may hit each other, they need to have hit each other hard enough to reach activation energy. It is when they reach activation energy is when they react with each other. The rate of the reaction is when more successful collisions happen per second. The reason why the rate of reaction is faster when the solution is more concentrated is that the ions are closer together in a concentrated solution. The closer together they are the more frequent do the ions collide.
Method and Equipment:
Equipment -
- Beakers – To put both of the reactants in/diluted Acid
- Measuring cylinders – To measure out the right measurements for the dilutions and Sodium Thiosulphate.
- Black cross – To place underneath the beaker that has both of the reactants in.
- Distilled water – Used for diluting the HCL and washing out the equipment.
- Bottle A = 2mol/dm3 Hydrochloric Acid
- Bottle B = 1mol/dm3 Hydrochloric Acid
Method:
1. Set up equipment, put everything needed for Hydrochloric acid on one side and mark it A, and everything needed for the Sodium Thiosulphate on another side of the table marked B. This is so there is no contamination of the two liquids making the test unfair.
2. Make Acid dilutions.To make less than (1mol/dm) use the bottle of (1mol/dm) Hydrochloric Acid, for the (2mol/dm) there is a designated bottle. (Make enough for the experiment to be repeated 3 times)
3. After making all of the dilutions, wash equipment with distilled water; place the black cross underneath a clean beaker.
4. Add both liquids (following the measurement table below) to the beaker and time how long it takes until the cross cannot be seen. Make dilutions for 1.75, 1.25 0.75, this will allow for results to be even more reliable so we can check in between the acid dilutions as I original predicted.
5. Repeat each dilution three times to get an average.
Fair Test:
- Na2S2O3 25cm3 each time.
- Acid strength varied but volume stayed the same.
- Cleaned all the equipment after use, to avoid contamination.
- Same temperature each time.
- No catalyst used in any reaction.
Results:
* Anomalous result, repeated to ensure accuracy.
Analysis:
What I saw:
I noticed in the experiments that the less diluted the Hydrochloric acid was, the more rapidly it reacted. With the more diluted acids like 0.25 and 0.125 molar they started to react around 15-20 seconds but it took a lot longer for the cross to disappear.
Why it happened?
This is because the particles of Acid are less present so the Sodium Thiosulphate particles have less to react with; they have to go searching for the acid, and as there is more water particles present it is harder for them to have a successful collision with the acid particles.
As you can see the slope going top to bottom is indeed on both lines, this proves that I was correct in my prediction about the more diluted the acid is, the longer it takes for it to react.
Although it proves that, the times those selves are very different. Instead of having them double each time, they have increased yes, but on very small amounts.
Each time they roughly increased around 4/5 except for 40.13 to 52.98, that increased by a shocking 13 second, this could have been for many reasons…
- Contaminated glass wear
- Wrong dilutions
- No successful collisions with the particles for a long time.
I didn’t really get any odd results on my experiments, only on my averages.
Now moving on to the rates, and how the concentration affected them…
The pink line shows my prediction, seeing as my prediction was based on maths and halving the rate each time, it will appear to be straight. But the direction of the lines is both sloping downwards. Although they don’t have the same gradient they both share the same principal…The more diluted the acid is the slower the reaction, the lower the rate.
Evaluation:
Over all I think the experiment went quite well, although I would improve it in a few ways…
- Instead of using the “watching the cross” disappear method, use a light meter, that way its more accurate as to when an amount of a reaction has taken place.
- Instead of just washing the equipment out with distilled water each time, get a new clean beaker for the reaction to take place in, this will avoid any left over from the last experiment.
- Instead of using a measuring cylinder use a burette or a pipette to get really accurate measurements.
