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1mol/dm3 of Hydrochloric acid
- Heating equipment. E.g. Bunsen burner, Water bath.
- Thermometers
- Straws
- Test Tubes
- Pipettes
- Usual Glassware (Beakers, Boiling tubes, etc.)
- Agar Borer
There are 3 main factors affecting the rate of diffusion. These are:
- Temperature
- Surface Area
- Concentration
Temperature affects the rate of diffusion in the way that heat gives energy to the particles. This causes the particles to move around faster over a larger distance. This results in the particles spreading out over a wider area of space faster than if they were at normal temperature, hence diffusion would be faster. However if you lower the temperature it will have the opposite effect on the particles. The particles will lose energy and will slow down resulting in the cold, slow particles not covering as much space as the hotter, faster particles. This means that the diffusion will take a much longer time.
Surface area affects the rate of diffusion in the way that the larger the surface area, the more space there is for the particles to diffuse through, which therefore means a faster rate of diffusion. This means that if you want I wanted the experiment to have a fast rate of diffusion I would somehow have to give the agar block a small mass but a large surface area. If the agar block had a large mass and a large surface area it would still take longer than the small mass and large surface area. This is because there would be more mass for the HCl to diffuse through, meaning it would take longer.
Concentration affects the rate of reaction in the way that the more particles of HCl per cm3, the more particles of HCl are going to diffuse into the agar blocks. This is because there will be a higher ratio of HCl particles diffusing into the agar blocks at one time, resulting in a faster rate of diffusion.
In my experiment I have decided to study the affect of concentration on the rate of diffusion. From my scientific knowledge and previous experiments I predict that at the higher concentration, the rate of diffusion will be faster. At the lower concentrations I predict that the rate of diffusion will be slow or, if possible, close to none.
This is how I will set out my apparatus:
For the experiment I have decided to stay at room temperature but vary the concentration. This table shows how I will dilute the concentration.
As you can see from the table above, the concentrations that I have decided to use are 1, 0.9, 0.7, 0.5, 0.3 and 0.1. I have also decided to perform the experiment 3 times in order to gain a good set of results. I will then take the results I have taken and calculate average times.
In order to make the test fair I will have to keep the volume of the agar the same each time I perform the experiment. If the volume of agar differs then so will the surface area, affecting the rate of diffusion. I will ensure that the volume of agar is kept constant by either preparing the necessary agar blocks before the start of the experiment or double-checking to make sure I have bored the right size block of agar using the agar borer each time I repeat the experiment. I will also keep the volume of the HCl constant in order to maintain a fair test. I will do this by measuring the necessary amount of HCl using an accurate measuring instrument such as a pipette.
In order to test out my experiment plan I performed a preliminary investigation at room temperature. These were the results I achieved:
For my experiment I have chosen to use a straw, which has a diameter of 3mm, in order to save time.
From the preliminary results I still feel that by increasing the concentration, the rate of diffusion will increase and hence the time taken for the HCl to diffuse into the agar block will be quicker.
