Rates of reaction - molarity Essay Example for Free

Rates of reaction molarity Essay Chemistry Coursework Rates of Reaction Molarity (Concentration) Aim: to find out if the concentration of HCl affects the amount of hydrogen gas given off when a magnesium strip is added. Apparatus: Gas syringe to take all the gas from the reaction and measure it Test tube to hold the two reactants Measuring cylinder to measure amount of water and acid Stop watch to time the reaction Delivery tube to deliver the hydrogen into the gas syringe Ruler + Scissors to measure and cut the magnesium Reactants: Magnesium strip Hydrochloric acid 2HCl + Mg H2 + MgCl2 Preliminary Work: From preliminary work I have found out that using 20 cm3 of acid and using 2 cm of magnesium for 1 minute gives off sufficient gas to measure accurately and I also found that for the molarity I should not go lower than 0. 6 as there of gas given off will be too slow. This is how I did the experiment: I set up the experiment as shown above   Added 2 cm of magnesium strip to 20 cm3 of HCl   I then wrote down the volume of the gas every 5 secs for 1 minute of the reaction   Use concentrations   M to see which would be suitable. Scientific Knowledge: A chemical reaction needs reactant particles to collide successfully for it to take place. For the chance of a successful collision to take place more frequent collisions need to occur. These four factors affect the frequency of collisions therefore affecting the rate of reaction: Concentration there are more acid particles in the same volume so they are more likely to collide with the magnesium particles. Temperature when the temperature is increased the particles gain kinetic energy, which means the particles vibrate more which in turn means they are more likely to collide successfully. Surface Area a larger surface are means more particles are exposed. Therefore as larger number of collisions occur Catalyst the catalyst lowers the amount of energy needed for a collision without taking part therefore more successful collisions will take place. However I am only testing concentration so from this knowledge I know that the higher the concentration the more likely that the particles will collide. Prediction: I believe that as the molarity decreases so will the speed at which the gas collects. I predict this because of my preliminary work and scientific knowledge. This knowledge is that as the concentration increases there are more particles in the same volume so then there will be more successful collision. This means the volume of gas collected in the first minute should decrease as the concentration decreases.   Set up the experiment as shown above   Add 2 cm of magnesium strip to 20 cm3 of HCl   Write down the volume of the gas every 5 secs for 1 minute Use concentrations M To make the different concentrations I added water to 1M hydrochloric acid: Molarity Water/Acid cm3 1 Fair test/Reliability: By controlling all the other variables (temperature, surface area and using a catalyst) I am leaving only one thus making my results accurate and reliable and easier to test. I am also using the same amount of acid (variable) and magnesium each time making it a fair test. I have also repeated my experiment so that I can average out my results making it fair, as extremities will be averaged out. To make it a reliable and fair test I have made sure that the gas syringe is always at 0 at the beginning of each experiment and I will start the clock as soon as the Magnesium meets the HCl and always make sure that the Mg is cut to exactly to 2 cm. Safety: Always wear goggles so that no acid can go in your eye Wash acid after using acid so that acid does not transfer onto things that you touch and worse in your mouth (from the food that you eat). Results: Test 1 Molarity (M) Water/Acid cm3 T 5s I 10s M 15s E 20s 25s I 30s N 35s 40s S 45s E 50s C 55s S 6Test 2 Molarity (M) Water/Acid cm3 T 5s I 10s M 15s E 20s 25s IVolume of H2 collected Rate of Reaction: The rate of a reaction is how quickly the reactants turn into products. To work out the rate of reaction I have decided to find the time that each reaction took to reach 8 ml of H2 and converting it into a rate. The formula for Rate of Reaction is 1/time (secs) Molarity (M) Calculation Rate (3dp)   The rate of reaction tell you how fast each reaction takes to get to point as you can see from my rate of reaction graph as the molarity increases the reaction is quicker apart from 0. 8 (sources of error in evaluation). This graph is useful, as initially I has thought 0. 7 moles was the incorrect result but this graph proved otherwise. Also from this graph I can find out what the rate should have been for 0. 9 ideally which is 0. 036 so the time it would have taken for this experiment to reach 8 ml of H2 is 1/rate = 1/0. 036 = 28. 7 seconds. I can also predict other results:   Conclusion As my graphs and results show the volume of gas produced in the first minute increases with the increase in molarity apart from 0.8 moles, this anomaly occurred both times which is unusual but apart from that result I know that Molarity is proportional to volume of gas collected per minute. E. g. it takes longer for 8 ml of gas to be collected as the concentration reduces, which proves my prediction right. This is because there are more particles in the same volume if the concentration is increased. Here is a diagram: Less moles More moles Evaluation I believe the plan was good and enabled me to get the results that I needed. My experiment went very well apart from my one anomaly (0.8 Moles) this is unusual as it happened both time as but these are some reasons why this happened: Sources of Error Gas syringe was only to the nearest ml Magnesium it used up the HCl around it and turned it into MgCl but did not react with the acid at the bottom making the reaction slower Heat as the Mg reacts with HCl heat is given off speeding up the reaction Human Error reading the gas wrong, starting or stopping the clock at the wrong time etc. Solving these Errors Gas syringe use a position sensor on the gas syringe, which is attached to a computer. This will record the results with no anomalies. Magnesium shake the test tube every so often Heat cant solve this, the reaction is exothermic Human Error use a position sensor on the gas syringe, which is attached to a computer. This will record the results with no human anomalies. Extension To extend the investigation I would do the experiment again put try and put right all the sources of error and see if my results come out perfect. Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section.