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Factors affecting Osmosis in Potato Tissue Background Scientific Information: Key Variables: There are several variables we must consider. These are: 1. Length of potato chip 2. Mass of potato chips 3. Temperature 4. Variety of potato 5. Volume of salt solution 6. Duration 1. We must keep the length of potato chip the same because if some are longer than others then they have a larger surface area which will affect the rate of osmosis. 2. We have to weigh the potato chips at the beginning of the experiment and at the end so that we can measure the increase or decrease in mass.
3. The temperature must be kept the same as an increase in temperature may increase the rate of osmosis. 4. The variety of the potato is kept the same because 5. We keep the volume of the salt solution the same because if there is less salt solution in some of them then 6. We keep the duration of each experiment the same to make sure the experiment is a fair test which is why we keep all the others the same as well. To make this experiment a fair test we can only change one thing. This is the concentration of the salt solution. This is the independent variable. Hypothesis:
I predict that if we double the concentration of the hydrochloric acid then the reaction rate will double. We are going to use a range of 3 to 1 molar so we have two doubles which are 1 and 2 and 1. 5 and 3. The results will be directly proportional. I can predict this because of the collision theory. The collision theory shows that if the concentration of one of the reactants is doubled then the total number of collisions occurring will double and therefore the rate of reaction will also double. For a reaction to occur, the particles must collide with each other.
Most collisions are not successful and the particles just bounce apart. The rate of the reaction depends on the number of effective collisions so therefore if everything is kept the same and the only thing changed is the concentration of the hydrochloric acid, then when the concentration is doubled so should the number of collisions and so the rate of reaction should be doubled. There are several factors which affect the frequency of the collisions. The first one is surface area. The larger the surface area, the more space there is so the more likely the particles are to collide.
Concentration and pressure are both similar. If the pressure is high then the particles are closer together in the same amount of space so there is less space for the particles to miss each other. If a catalyst was being used it would affect the reaction in this way; the catalyst sticks one set of particles together so that they can not move. This means that the other set of particles can find it more easily because the ones which are stuck together are not moving. The last one is temperature. The higher the temperature, the more energy the particles have.
This means that they move around more quickly and collide more frequently A rate of reaction can be increased by either increasing the total number of collisions which take place or by increasing the number of effective collisions. Safety: While doing these experiments we must consider the safety factors. I must wear safety goggles at all times because the salt solution may get in our eyes and be irritating. I must wear a lab coat in case some of the salt solution gets on my skin. I must not eat or drink in the lab as this is unhygienic.
Preliminary Method: Apparatus: A raw potato 5 plastic cups White tile Cutting machine Forceps Diagram: Preliminary experiments We completed our preliminary results and found that we had to make a change to our original plan. We did an experiment with four centimetres of magnesium and three molar of hydrochloric acid. The reaction was over within ten seconds and was far too quick for us to measure the amount of gas collected. We did the same experiment but instead of four centimetres of magnesium ribbon, we used six. This was also too quick to measure.
We then did eight centimetre of magnesium ribbon and this was a measurable speed so we decided to use this. We then did the experiment for 8 cm magnesium ribbon and 1 molar hydrochloric acid. We needed to try the highest and the lowest concentration of hydrochloric acid and if they worked then the ones in between would work and we wouldn’t have to test them. For the experiment for three molar we had to measure the volume of gas every three seconds because the reaction was over very quickly and if we had measured the gas every ten or twenty seconds then we wouldn’t have enough points to plot a graph.
We tried to measure the experiment for one molar every 3 seconds but the reaction was way too slow and we had far too many points to be able to plot them on a graph. At the end of our preliminary experiments we found that we could use a range of 1 to 3 molar and 8cm of magnesium ribbon. Preliminary results: These are the results for 3 molar hydrochloric acid and 8cm magnesium ribbon. Time (s) Volume of hydrogen (cm ) We can see from these results that although the reaction is relatively fast, it is not so fast that it is impossible to measure the rate of reaction.
These are the results for 1 molar hydrochloric acid and 8cm magnesium ribbon. Time (s) Volume of hydrogen (cm ) 95 Method for real experiments: We are using the same method for our actual experiments as we did for our preliminary experiments.. We will measure out a piece of magnesium ribbon which is eight centimetres long. We will then measure out the hydrochloric acid and water solution which will always have a volume of 30 cm . We will put the hydrochloric acid into the side armed flask.