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Rates of Reaction

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Introduction

Rates of Reaction coursework Aim: My aim is to see how the concentration of hydrochloric acid affects the rate of reaction, using marble chips. Prediction: Primarily I state my hypothesis to be; that the increase in concentration (hydrochloric acid) of reactants will increase the collision frequency between the reactants, this and calcium carbonate. Therefore the effective collision frequency also increases. A chemical reaction is where the molecules of reactants either combine or separate, in this case we are looking at the displacement of the between calcium carbonate and hydrochloric acid, below is the formula for this reaction: 2HCl (aq) + CaCO3 (s) ----> CaCl2 (aq) + H2O (l) + CO2 (g) Hydrochloric acid + Calcium carbonate --> Calcium chloride + water + carbon dioxide Reactants: 2HCl (aq): hydrochloric acid (aqueous) CaCO3 (s): calcium carbonate (solid) Products: CaCl2 (aq): calcium chloride (aqueous) H2 O (l): water (liquid) CO2 (g): carbon dioxide (gas) I will now state the principals of the collision theory in order to elucidate the reaction. Max Trautz and William Lewis first proposed this theory in 1916 that qualitatively explains how chemical reactions occur and why reaction rates differ depending on the reactants and reactions. It assumes that for a reaction to be successful the reactant particles must collide, but only a certain fraction of the total collisions, the fruitful (successful) collisions, cause the transformation of reactant molecules into products. Furthermore factors, which contribute to whether the particles successfully collide and react, vary from speed, the angle of collision and consequently the orientation of the molecules when they collide. In relationship to this experiment, the higher concentration of hydrochloric acid added would result in a higher collision frequency, meaning that more particles will collide with each other, which would conclude in more successful reactions taking place. The fraction of the molecules have sufficient energy and the right orientation at the moment of impact to break the existing bonds and form new bonds; The minimal amount of energy needed so that the molecule is transformed is called activation energy (Ea), this is also known as threshold energy. ...read more.

Middle

Time (S) 0 10 20 30 40 50 60 70 80 90 100 110 120 Volume of gas (cm) 0 5 21 25 30 35 42 53 64 74 83 92 103 As you can see from the results that there are no decimal points and furthermore we have not rounded up or down neither showing attaining accurate results is very difficult when using this method. I will not be using this method due to its unreliability, for example the loss of gas and it not being a fair test; these were crucial to the experiment and should have not been affected in anyone as it simply destroys the purpose of conducting it. Method 2: Mass method An alternative way of finding how the rate of reaction is affected is to examine the mass as the experiment carries on, this again would tell us the amount of gas (carbon dioxide) being produced. This method is undertaken by using a top pan balance to measure the amount of carbon dioxide given off in gaseous exchange through the loss of mass by the solution. I will use the apparatus as follows: We first gathered the equipment and set it up as shown above, we then measured the mass of the solution at 0 minutes which was a total of 50g, We then continued the experiment for seven minutes, every one minute interval we measured the loss of mass from the solution. Time (mins) 0 1 2 3 4 5 6 7 Mass (g) 50.00 48.81 48.70 48.64 48.61 48.59 48.57 48.55 Loss in mass (g) 0 1.19 1.30 1.36 1.39 1.41 1.43 1.45 Due to the results remaining too consistent throughout there was not much drastic change so we could not tell whether carbon dioxide was being released through gaseous exchange; showing that this method is also unreliable. Furthermore this method took far too long when obtaining the results meaning the results could not be accurate as the collision frequency was evidently far too low as the rate of gas given off was too unreliable and waiting one minute only extended the actual experiment further. ...read more.

Conclusion

Extension Aim To see how the concentration will affect the rate of reaction by measuring the mass lost in a reaction. Prediction I believe that that the concentration will be proportional to the rate of reaction thus simply meaning that the loss of mass from the solution will be proportional to the concentration as well. This is evidently due to the collision theory, which is explained in my initial prediction. I have decided to improve the experiment from the preliminary tests in order to see whether I can improve its accuracy when obtaining the results. Method Equipment -Marble chips (identical and possess same mass to ensure fairness) -Hydrochloric acid (0.5M,1.0M,1.5M,2.0M, 2.5M and 3M) -Stirring rod -Stop clock -Balance (accurate too 0.001g) -Spatula -Conical flasks -Syringe 1. I will use a measuring cylinder and place 30ml of hydrochloric acid into a conical flask. 2. I will put the flask on the top hand balance accurate to 0.001g 3. I will then attain the mass of the conical flask and the marble chip and add them together (without adding the chip in the flask). 4. i will then put the marble chips into the flask and start the stop clock immediately. 5. The flask will be connected to the syringe yet again though this is primarily to try and look at the volume produced and the loss mass of the solution in order to be as accurate as we can. 6. I will take the readings of the balance every 15 seconds for 5 minutes, as I think this would be the time need in order for the whole chip to be consumed. 7. I will repeat the tests, but use a different concentration of hydrochloric acid. Diagram: Results table Time since start of reaction Total amount of mass lost (g) Average Amount of mass lost (g) Volume of gas produced (cm�) (seconds) Attempt 1 Attempt 2 Attempt 3 1 2 3 0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 ...read more.

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