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"How concentration of acid changes the rate of a reaction".

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Introduction

Acid rain background information: The problem with fossil fuels is that, on combustion, they release acidic gases such as carbon dioxide. These gases are carried away by air currents, sometimes travelling hundreds of miles before they dissolve in atmospheric water vapour. The acidified vapour condenses and is precipitated as acid rain (or snow). Acid rain causes the erosion of stonework and may kill plants and trees. Some forests, such as Germany's Black Forest, may be irreversibly damaged if acid rain emissions are not diminished. Acid rain also dissolves some poisonous metals, thereby introducing their ions into the water supply and damaging the aquatic life. 400 lakes are being fishless in Norway and north- European because of these dumps. (From Chemistry book page 60) 1908 1968 2) List of Apparatus: > Hydrochloric acid (0.25, 0.5, 1.0, 1.5 molars) > Limestone chips(size: large) > Gas syringe > Beaker > Stand and clamps > Gas syringe holder > Stop watch 3) Variables The variables I will be considering are: > Surface area of the limestone chip(s). > Temperature at which the reaction takes place. > Volume of acid. > Molarity of acid. Each of the variables above affects the rate of reaction in their own ways. The pressure of the experiment causes the reaction to occur quicker as with more pressure there will be more gaseous particles and less space for the particles, so the particles will strike each other more frequently. With the Surface area of the limestone chip(s), there will be more for the acid particles to react with, as the total surface area will be more thus more particles of the limestone chip. The temperature at which the reaction happens does not really have an effect in this case, but it can be an important variable in another investigation. ...read more.

Middle

The amount of Hydrochloric Acid (20ml in my case) has to be constant also. There are quite a few reasons why these factors are important. If the mass of the Calcium Carbonate varies then the Hydrochloric Acid will have more, or less, surface area to react on which would change my results greatly. Same for if I have more Hydrochloric Acid in my beaker, then the Calcium Carbonate will have more to react on and that would be unfair as well. 3) Prediction: I predict that as the Molarity of the Hydrochloric Acid increases, so will the speed of the reaction in the gas syringe. I predict that the higher the concentration of acid then the faster the rate of reaction. Calcium Carbonate + Hydrochloric Acid => Carbon Dioxide + Calcium Chloride CaCO3 + 2HCl => CO2 + H2O + CaCl2 I predict this because when a chemical reaction takes place, the atoms are broken loose from their arrangements and re-arranged into different groupings, forming new substances. The reaction above can only happen if the particles of acid came into contact with particles of limestone. In gases and liquids or in solutions, the particles are moving around freely and can bump into each other more easily. In this reaction of acid and limestone, if the acid is very concentrated this means that there will be plenty of acid particles close together in the solution. Acid particles collide with the calcium carbonate very frequently and if they do this, the surface of the limestone will dissolve quickly. If the acid is very dilute then the particles will be more spread out. They will bump into the limestone a lot less often and so the reaction will take longer. ...read more.

Conclusion

Then I wouldn't have muddled up my timings when I conducted my experiment on the 1.5Ms of Hydrochloric Acid, that is one major improvement I could have made; I could also have made several other minor improvements when I look back on the rest of the experiment. Like the fact that I had a jumpy syringe and that my results were slow in some places due to the jumping around of the syringe. I could have made sure that the syringe actually worked. Overall I think that the way that I carried out the experiment was probably the best way to do it because it was short and simple without taking great detours around the actual point. If I were to do the experiment again, like I said before, I would have checked the equipment first but otherwise nothing really would have happened. My results seemed to be reliable except for my 1.5M ones. I made a rate chart and all the others looked reliable. The 1.5M results really didn't fit into the main pattern but still it was all right. I may, therefore, as further investigate into the effects of the other factors that effect rate of a reaction in HCL and CaCO3 again compare my results with these and I would investigate the effect of the surface area at which the reaction occurred, the temperature of the reaction I would also use because as I mentioned it can affect the rate of reaction immensely. I think that I had enough correct results to draw a conclusion. It would have been better if my 1.5M experiment had worked but the 1.5M going wrong actually helped my conclusion in a way. I am confident that I was to draw an accurate conclusion. I could have conducted a few more experiments to get my accuracy level to a higher level. BY:FRED ...read more.

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