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The variable that I will change will be the temperature of the water that the Alka Seltzer is put in.

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SKILL P: PLANNING Ibrahim Abu-Abdo Statement of the problem: The variable that I will change will be the temperature of the water that the Alka Seltzer is put in. For my results I will measure the time taken for the Alka seltzer tablet to completely dissolve in water at different temperatures. Input variables: * Varying surface area of Alka-Seltzer tablet, i.e. if cut into smaller pieces or crushed it will increase the surface area. (If the surface area is increased (more powdered) the rate of reaction also increases. This means that there are more collisions between the solid and liquid.) * Amount of tap water H2O used, i.e. volume (ml). * Amount of Alka-Seltzer tablets used, i.e. quantity of tablets. (one is used) * Number of times the solution is stirred. (If the solution is stirred more there are more collisions between the particles therefore the reaction is speeded up.) * Temperature of Water-�C. (As the temperature increases so does the rate of reaction. By increasing the temperature, particles move faster, i.e. they have more energy. So, they collide with more energy and more frequently.) * pH of Solution: Water has pH of 7 at 25�C. As the pH decreases, i.e as the solution increases in acidity, the rate of the reaction increases as well. Output Variables: Rate of reaction depends on all the 6 points I have stated above: * If the surface area of the tablets is increased by crushing, the particles around it in the solution will have more area to work on, and the rates of reactions will increase because there will be more collisions. Complete reaction will finish faster. * The more amount of water used as we increase the temperature, the quicker the tablets will dissolve because there will be more water particles to collide with. So the rate increases. * If the amount of tablets being used is increased for the same amount of water, i.e as concentration increases, rate will increase as well because there will be more collisions between particles. ...read more.


Particles react when they collide with sufficient energy. At a higher temperature collisions are more frequent, and they also have more energy, both because particles are moving faster. At a higher concentration collisions are again more frequent, as there are more reactant particles in the liquid. So, more tablets, means more collisions. Increased surface area of the solid again increases the frequency of collision between reacting particles, as the liquid reactant has greater contact with the solid one. Rate of reaction can also be increased by adding a catalyst, but there is not one for this reaction. If we use an acidic solvent instead of water, example vinegar, the collision increases than that of water because base particles in the tablets will have more acid particles to collide with. I.e. the ones in the tablets and the ones in the solvent. Hence higher rate of reaction. 8. Knowledge about tablets Alka-Seltzer tablets contain sodium hydrogen carbonate (NaHCO3) and citric acid (C6H8O7). Both are solids, so no reaction will occur between the base(s) and the acid(s) until the tablet dissolve in water or get wet. Both have to be in aqueous form to react. When this happens, hydrogen ions (protons) transfer from the acid to the base according to the neutralisation reaction. In my experiment, the base is a metal hydrogen carbonate (NaHCO3) So: Acid + metal hydrogen carbonate Metal salt + Carbon dioxide + water Citric acid + Sodium hydrogen carbonate sodium Citrate + carbon dioxide + water C6O7H8 (aq) + NaHCO3 (aq) Na (C6H7O7) (salt) + CO2 (g) +H2O (l) As a consequence of this reaction, bubbles of carbon dioxide are produced (the fizz) and a basic solution (due to the excess of sodium hydrogen carbonate as well as the sodium citrate in solution). As long as carbon dioxide is produced, I believe that the reaction is still going on. Note: Formula of citric acid: HOOCCH2C (OH) (COOH) CH2COOH If we take tablets as medicine, the reaction above will neutralise excess stomach acid. ...read more.


Evaluation: My results were very reliable, because by looking at my graphs I can see a trend which relates to my scientific background. It is also evident that I have obtained a reliable set of results when I see that the replicate shows the same trend as the first experiment. I used a measuring cylinder and a beaker to measure out the amounts of water; however these did not seem to affect the quality of my results. To increase the accuracy of my results I could have perhaps used a burette. Even though I did the best I could to keep the experiment accurate, at some places there were mistakes that unintentionally occurred. Firstly, when testing temperatures at 30�C and 40�C, the water was sometimes heated more than needed, so I had to wait until it cooled down to the required temperature. To avoid this happening, a thermostatic water bath could have been used, because I could set it to my required temperature. Also it would mean that the solution inside it would reach the exact temperature or close to It., and not increase or decrease once the water inside it has reached equilibration. It was also very difficult for me to observe exactly when the Alka-Seltzer tablets had totally dissolved and consistently decide this for every result obtained. This was probably the main factor that would have decreased the accuracy of my readings. To avoid this happening I would have needed to use specialized piece of equipment which would tell me exactly when the tablet was dissolved Overall, I can come to firm conclusion from my results that support my prediction and background knowledge that: As the temperature increases, less time will be required for a reaction to take place i.e. the rate of reaction increases. To improve the experiment overall I could use distilled water to avoid inaccuracies related to the hardness of tap water. I believe I should get a straight line curve. Another improvement I could have made is to increase the range of the temperatures investigated. (10�C to 100�C). 1 ...read more.

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