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Indicator Lab Report - investigating acid-base reactions

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Introduction

Data Collection Uncertainties Apparatus Uncertainty Significance Burette � 0.05cm3 Insignificant. This uncertainty is very small, and so it is negligible. Pipette � 0.06cm3 Insignificant. This uncertainty is very small, and so it is negligible. pH Probe � 0.005 Insignificant. This uncertainty is very small, and so it is negligible. Below is a table showing the change in pH as an increasing amount of a base is added to the acid, thus changing pH. pH was monitored using a pH probe and the data was interpreted using Logger Pro. The thicker line represents the equivalence point. The concentrations of all substances was 0.5 molar. The amount of acid being titrated has a volume of 20 in all experiments. pH Change with Volume: Titrating HCl with NaOH Volume of Base �0.05cm3 pH �0.005 0.0 1.13 2.0 1.15 4.0 1.30 6.0 2.14 8.0 12.28 10.0 12.73 12.0 12.81 14.0 13.06 16.0 13.04 18.0 13.11 20.0 13.11 22.0 13.21 24.0 13.24 26.0 13.26 28.0 13.27 30.0 13.31 pH Change with Volume: Titrating CH3COOH with NaOH Volume of Base �0.05cm3 pH �0.005 0.0 2.95 2.0 4.34 4.0 4.7 6.0 5.56 8.0 11.91 10.0 12.56 12.0 12.74 14.0 12.85 16.0 12.89 18.0 12.94 20.0 12.98 22.0 13.02 pH Change with Volume: Titrating HCl with NH3 Volume of Base �0.05cm3 pH �0.005 0.0 1.15 2.0 1.1 4.0 1.1 6.0 1.12 8.0 1.15 10.0 1.19 12.0 1.23 14.0 1.27 16.0 1.32 18.0 1.37 20.0 1.42 22.0 1.48 24.0 1.51 26.0 1.61 28.0 1.68 30.0 1.75 ...read more.

Middle

The strong acid, HCl, dissociated into H+ and Cl- ions, whereas the molecules of the CH3COOH do not fully dissociate, so it was considered a weak acid. Fully dissociated molecules such as HCl produce more H+ ions than partially dissociated ones such as CH3COOH, and so these have a higher concentration of hydrogen ions. In a solution of ethanoic acid, an equilibrium is present, meaning both forward and backward reactions take place, and so there will be less H+ ions in this solution, since it will sometimes be in a molecule and sometimes an individual ion. This does not apply to HCl, which permanently dissociates into H+ and Cl-. This concentration of H+ ions immediately affects the pH due to their inverse relationship. The NaOH was considered as the strong base since the molecules fully dissociate into Na+ and OH- molecules, whereas the molecules of NH3 cannot directly produce OH-, and must react with water to produce ammonium and OH-. The same theory applies to bases as acids; fully dissociated molecules such as NaOH produces more OH-, which means there is a smaller concentration of H+, reducing the concentration and so heightening the pH due to the inverse relationship. Ammonia reacts to form ammonium and OH- in a reversible reaction, so at anytime, there is a small amount of OH- present, so the pH does not increase significantly. ...read more.

Conclusion

An ideal amount of repetitions for each titration would be 5. This would ensure that the chemicals being tested show the same trends in the graphs and that the graph is indeed the correct one for the titration in question. The experiment could be carried out with a number of different weak and strong acids and bases, not only the ones used in this investigation. This would provide more substantial results and eliminate the assumption that the titration curves in this experiment apply to all strong and weak acids and bases titrations. More NH3 should be added in the weak base and strong acid titration so the equivalence point can be reached and the data can be properly processed. As mentioned before, uncertainties were not a problem in this investigation, but they could be further reduces by using more accurate equipment which can measure the volume of a liquid to a number of decimal places. The last area for improvement, assumptions of purity and other reactions, can be monitored by measuring the actual yield of products and comparing it to the theoretical yield of products, the difference would be assumed to be due to purity and other reactions. This is calculated with the formula below: Percentage Difference = (Actual Percentage - Theoretical percentage) / Actual Percentage. Error Uncertainty or Assumption Significance Data set limitations Equivalence point not reached for one graph By adding more alkali, the equivalence point could be determined and, by doing so, the buffer region and 1/2 equivalence point could also be determined. Uncertainties Assumptions of purity ?? ?? ?? ?? ...read more.

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