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Investigation to Discover the Factors Affecting Rates of Diffusion between Agar blocks and Hydrochloric Acid.

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Investigation to Discover the Factors Affecting Rates of Diffusion between Agar blocks and Hydrochloric Acid. In this investigation I hope to discover the factors affecting the rate of diffusion between Agar blocks and Hydrochloric acid. I will hope to measure how varying either the concentration of the acid or the temperature affects the rate of diffusion. I will try the experiment with a consistent size of agar blocks, but varying concentration and note down the times it takes for each block to diffuse completely. I will be given a 1cm deep agar plate containing 1% agar. The agar has been made alkaline by the addition of NaOH (Sodium Hydroxide) and stained pink using phenolphthalein. As the HCl diffuses into the agar, the alkali is neutralised and the phenolphthalein becomes colourless. I will time how long it takes for the acid to diffuse into the different size blocks of agar. The equipment I will be able to use in the experiment is listed below: * 1mol/dm3 of Hydrochloric acid * Heating equipment. E.g. Bunsen burner, Water bath. ...read more.


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. ...read more.


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: Diameter Time 12mm 6m30s 8mm 6m7s 6mm 5m17s 4mm 3m52s 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. Stuart Stephens 11D 3 ...read more.

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