Sunday, September 1, 2019
How the PH changes during a titration experiment Essay
Having a higher concentration of alkali will mean that there will be more molecules closer together for the acid to collide with. This will speed up the reaction as collision theory suggests that molecules have to collide to react and if there are more molecules to collide with the reaction will happen faster as there is a higher chance of a collision. Volume of alkali An increase in volume would mean that the neutralisation would take longer as you would need an equal amount of the same strength acid in order to neutralise it. Furthermore in collision theory if there is a bigger space that the molecules are in then the molecules are less likely to collide which means that the reaction would be slowed. Concentration of the acid Having a higher concentration of acid would like having a higher concentration of the alkali would speed up the reaction. This is because collision theory states that if there are more molecules in a set area there is a higher chance of the molecules colliding with each other which would speed up the reaction. Volume of the acid An increase in the volume of the acid would mean that the reaction would be slowed. This is because you need the same amount of acid and alkali to reach PH 7 or neutral. This is because it would be the same amount just in a larger space reducing collisions. Temperature A higher temperature would mean that the molecules would have more energy this means that when they collide they would collide with enough force to start a reaction off. This speeds up the reaction as the molecules always create the reaction rather than glancing off of each other and not starting a reaction. Presence of a catalyst A catalyst holds one reactant in place so that another can collide with it directly and not glance off of it. This speeds up the reaction as more direct collisions take place. An example of a catalyst is Cobalt in the manufacture of ethanoic acid. The catalyst does not change the products orÃ get used up in the reaction. Hypothesis Increasing the concentration of the acid will increase the rate of neutralisation during titration. Increasing the concentration of the acid would mean that you would need to use less acid from the burette to neutralise the alkali particles as there would be more acid particles than alkali particles in a set area. I think that the volume of acid needed to reach the point of neutralisation will double from 0.8 to 0.4 and from 0.4 to 0.2. I have chosen to change the concentration of the acid as it will be easier to measure with the equipment we have. Furthermore it will be easier to set up as we have access to different concentrations of the acid such as 0.5 molar and 1 molar concentrations. Indicators Type of Indicator Advantage of Indicator Disadvantage of Indicator Universal Indicator It covers the whole PH scale so we would see how the PH changes during a titration experiment. A disadvantage is that it does not have a clear colour change so we would not be able to tell when it is exactly neutral. Litmus paper Has a definite colour change which we need in a titration experiment. However we could only tell if the solution was acid or alkali so we could not see how the PH changes. Phenolphthalein Has a definite colour change at PH 7 so it is very accurate for titration. It does not tell you whether the solution is acidic or neutral as it is colourless at acid and neutralisation. Methyl Orange Shows if solutions are acids or alkali. No definite end point at neutralisation. A will do a preliminary test with universal indicator to see which if it is accurate and precise in my titration experiment. If not I will use Phenolphthalein, as it has a definite colour change at PH 7, when I test howÃ changing the concentration of the acid will affect neutralisation. Preliminary Tests Equipment Equipment Why I will use it in my investigation Burette This will let me measure out the acid precisely and accurately unlike a measuring cylinder or beaker. Beaker I will use this as it will stop the alkali from spilling and will contain the alkali easily. Furthermore it is transparent so I can easily see the colour change. White tile I will use a white tile as it will enable me to see the colours much easier than on a tile of another colour such as red or black. Measuring cylinder This will enable me to measure out 25mlÃ¡ µÅ' of alkali into the conical flask. Funnel A funnel will allow me to pour the acid into the burette without it spilling which will limit safety hazards. Hydrochloric acid 0.2, 0.4, 0.6, 0.8, 1.0 molarÃ 50cmÃ¡ µÅ' for each test. This is the acid that we are allowed to use and the highest concentration we can have is 1 molar to limit risks. Furthermore the school already has 0.2, 0.4, 0.6 and 1.0 molar already made up. Moreover I have picked five equally spaced concentrations because I will need I large range of results to identify a trend which will be easier if I have equally spaced concentrations. Furthermore I have not used over 1M because it is safer. Sodium Hydroxide 1.0 molar 25cmÃ¡ µÅ' for each test I will use this because it is already made up by the school. Furthermore it will limit risks as it is diluted sodium hydroxide. Burette holder I will use this so the burette does not slip over which could break it or spill acid making the test unrepeatable. Clamp stand I will use this so that I can clamp the burette onto it with the holder. This will stop the burette falling over and keep it upright so the acid flowsÃ properly. Universal Indicator I have chosen to try Universal indicator as it spans the whole PH scale so I will easily be able to judge when it is near PH 7 (Neutral). Preliminary work Method 1. Clear your desk so you have space to conduct the experiment. 2. Gather the equipment on the equipment list. Put on goggles for safety. 3. Attach the burette holder to the clamp stand and attach the burette to the holder. 4. Fill a beaker with water from a tap and fill the burette using the funnel to limit spillages, put the beaker under the burette and remove the funnel. 5. Run the water through the burette into a beaker to get rid of any chemicals left in the burette. 6. Add 50cmÃ¡ µÅ' hydrochloric acid to your burette using the funnel. 7. Add 25cmÃ¡ µÅ' of sodium hydroxide to your beaker using the measuring cylinder. 8. Add the universal indicator into the conical flask containing the sodium hydroxide. Mix. 9. Slowly add small amounts of the acid into the conical flask from the burette. Stop occasionally to mix the acid and alkali together. Repeat until the solution goes grass green. 10. Measure the amount of acid used on the burette record it. 11. Repeat steps 5-10 for all solu tions. Burette This will let me measure out the acid precisely and accurately unlike a measuring cylinder or beaker. Conical flask I will use this as it will stop the alkali from spilling much more effectively than a beaker and will contain the alkali easily. Furthermore it is see through so I can easily see the colour change. Moreover it is easier to agitate the solution. White tile I will use a white tile as it will enable me to see the colours much easier than on a tile of another colour such as red or black. Precise pipette/syringe This will enable me to measure out 25mlÃ¡ µÅ' of alkali into the conical flask much more accurately than a measuring cylinder could. Funnel A funnel will allow me to pour the acid into the burette without it spilling which will limit safety hazards. Hydrochloric acid 0.2, 0.4, 0.6, 0.8, 1.0 molar 50cmÃ¡ µÅ' for each test. This is the acid that we are allowed to use and the highest concentration we can have is 1 molar to limit risks. Furthermore the school already has 0.2, 0.4, 0.6 and 1.0 molar already made up. Sodium Hydroxide 1.0 molar Method 1. Clear your desk so you have space to conduct the experiment. 2. Gather the equipment on the equipment list. Put on goggles for safety. 3. Attach the burette holder to the clamp stand and attach the burette to the holder. So that it does not tilt or fall over to increase the accuracy of the results 4. Fill a beaker with distilled water from a bottle as the water is purified and fill the burette using the funnel to limit spillages, put the conical flask under the burette and remove the funnel. 5. Run the water through the burette into a beaker to get rid of any chemicals left in the burette. This will stop cross-contamination. 6. Add 50cmÃ¡ µÅ' hydrochloric acid starting at 0.2 and working up through the concentrations so that there is no need to keep washing the burette out which would change the concentration and decrease the accuracy to your burette using the funnel. Remove the funnel to ensure no extra drops of hydrochloric acid drop into the burette to make the results more acc urate. 7. Add 25cmÃ¡ µÅ' of sodium hydroxide to your conical flask using the glass pipette for precision. The conical flask will stop the alkali spilling out or splashing. It is also much easier to mix the alkali and acid during the experiment. 8. Add the Phenolphthalein into the conical flask containing the sodium hydroxide. Mix thoroughly in a clockwise direction. 9. Slowly add small amounts of the acid into the conical flask from the burette. Stop occasionally to mix the acid and alkali together. Repeat until the solution goes transparent. 10. Measure the amount of acid used on the burette and record it. Make sure that you are on the same height as the measurement so that you do not read it wrong as this will decrease accuracy. 11. Repeat steps 5-10 for all solutions of acid. Evaluation Equipment Improvements that could be made to our method Our equipment was not completely perfect and we had a few problems with some of it. The first problem we noticed was that the burette tilted forward and off to one side because the burette holder did not hold the burette upright however we had no other holders. This could have meant that the liquid flowed in a different way to if it had been straight. This may mean that the repeatability of our experiment is limited as our results may be because of this tilt. Moreover this tilt could have meant that our measuring of the acid and also our reading of the measurements could have been inaccurate as the liquid would have been deeper on one side of the burette. Therefore if I repeated this experiment I would use a burette holder that gripped directly upright so that I could have had a more accurate measurement of the volume of acid inside the burette at the start of our experiment. Another problem was that the end of the burette was chipped. Although it did not change the measuring of the liquid or the turning of the valve it could have displaced the hydrochloric acid differently to a burette which did not have the chip. This could have lowered the accuracy and reliability of my experiment. I increase the repeatability of my results I would have used a burette without a chip as this would have stopped the acid displacing differently to another burette. Evaporation of our solutions was also a problem. During our 0.2 molar tests we had to stop part way through due to the lesson timings. It was damp so the heating was on. This could have made some of our solution evaporate which could have caused inaccuracies with our results because the amount of acid in the burette and amount of alkali in the conical flask would have been less than we had thought. Moreover the temperature of the room fluctuated meaning that there could have been a faster reaction as collision theory suggests that temperature speeds up or slows down particles, Therefore our results could also be unrepeatable as our other tests would have different amounts of acid and alkali. Furthermore the reaction may have happened faster or slower as the particles would be moving around and colliding more at higher temperatures. If I were to repeat this experiment I would have used a laboratory which had no heating or a controlled heating system to avoid temperature fluctuations. I would have also done the trialsÃ all in one go so that my solutions did not evaporate. We also ran out of our original solution of 0.2 molar hydrochloric acid so we had to make more. This second solution may have had a slightly different concentration to the first. Moreover this would have lowered reliability because the results would have been changed because of this. Therefore at the start of our experiment we could have diluted a larger quantity of hydrochloric acid so that the solution would have stayed at the exact same concentration throughout the experiment. This would have made our results more repeatable as the range bars on my graph could have been much smaller. Human error could also have changed some of our results. Washing out and drying our equipment like conical flasks each time could have left drops of water or the previous solution in them. This would have lowered our concentration or cross-contaminated our solutions. This could mean that our results were not accurate as either the alkali already had been cross-contaminated by the acid or the alkali could have been at a lower concentration than the 1 molar that it should have been. To stop this we could have used a dishwasher to wash out our conical flasks and beakers. This would mean that the glasses would have been thoroughly washed and dried properly as the dishwasher would have evaporated all of the liquid moisture left in the conical flasks and beakers. Positive aspects of our method One good thing about our method was that we removed the funnel after pouring the hydrochloric acid into the burette every time. This would have made our results more accurate as after getting 50cmÃ¡ µÅ' in the burette no more acid dripped in. Therefore we were always starting at exactly 50cmÃ¡ µÅ' rather than 50.1cmÃ¡ µÅ' or 50.2cmÃ¡ µÅ'. Another aspect of our method that was good was that we got down to eye level to measure out the acid and alkali and also to see how much acid was actually used. This made our results more accurate as we did not read of the results from above or below the line which would have made our results seem lower or higher respectively. The biggest positive part of our method was that we got very good results, apart from one outlier, without anyone getting injured. This shows that my risk assessment worked as we avoided the hazards such as the possibility of the glassware breaking and the sodium hydroxide which was corrosive. Moreover, as our results were very close to the line of best fit and had very small range bars, our results seemed both accurate with a high repeatability. Therefore, overall, our method worked well. Evaluation of Results Our results were, on the whole, very good and supported my hypothesis that increasing the concentration of the acid will increase the rate of reaction. I am very pleased with my results as they were all very close to my line of best fit showing me that they were all accurate. Moreover, as my range bars are very small on all my results with the smallest range being 0.4cmÃ¡ µÅ' and the largest being only 1.8cmÃ¡ µÅ', they show that our results have a high level of repeatability. However it is possible that we had one outlier. Even though the line of best line still ran close to the result it increased our range bar for the 0.2 molar tests from 1.5cmÃ¡ µÅ' to 2.4cmÃ¡ µÅ'. Moreover the result seemed very low at only 109.6cmÃ¡ µÅ' when we did the 0.4molar tests as our average for that was 56.4cmÃ¡ µÅ' and as we were doubling the concentration the rate of neutralisation should have also doubled. Therefore we decided to repeat this test just in case and got 110.5cmÃ¡ µÅ' which was closer to the rest of the results and seemed to be closer to our line of best fit. Our outlier may have happened for several reasons. One is that we measured out a new batch of hydrochloric acid after doing this trial. This new batch could have been a different concentration to the original batch and therefore could have had a different rate of neutralisation. Another reason could be that the first batch had been cross-contaminated before we started the experiment. This may mean that the neutralisation took less time to complete as there was already some acid in the conical flask so the neutralisation process had already begun. The equipment not being washed,Ã by a previous group, could have been another reason for the outlier. If the conical flask had not been washed out there could have being cross-contaminated from a previous titration. On the other hand there may have being some water left in the flask which would have reduced the concentration of the sodium hydroxide. This would have increased the rate of reaction as there would have been less alkali particles for the acid to neutralise and react with.