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Introduction

Research Question: How does a change in the pH value of a solution of hydrochloric acid (HCl(aq)), affect how much zinc metal is reacted with the hydrochloric acid in a one minute time frame (rate of reaction), if the zinc metal is kept as the excess reactant across all variations in pH of the hydrochloric acid solution. Hypothesis: If the pH of a solution containing hydrochloric acid (HCl(aq)) is decreased by increasing the concentration of the hydrochloric acid, then the amount of zinc metal that is reacted by the hydrochloric acid solution should increase since, controlling all other variables, an increase in the concentration of reactants results in an increase in the rate of reaction. Variables: Independent Variable: The independent variable in this investigation is the pH of the solution of hydrochloric acid. I will change the pH of the solution by increasing/decreasing the concentration of hydrochloric acid in the solution, through dilution of a stock solution of a 12 mol dm-3 hydrochloric acid solution during the investigation. I will use the following variations of hydrochloric acid, aware of the fact that it is monoprotic: Concentration of HCl(aq) in solution (mol dm-3) Volume of HCl(aq) solution (dm3) pH value of solution (pH) 2.0 0.030 -0.30 1.0 0.050 0 0.1 0.300 1 0.01 0.500 2 For the most part, these variations and their associated pH values do not reflect a real world scenario, such as acid rain environments. However, the trend among them can be most easily studied and therefore the data collected can be applied as a trend to investigate how changes in pH values of acidic solutions affect the rate of reaction of zinc metal strips. For example, these results can be extrapolated to how quickly some aluminum-zinc metal alloys will deteriorate by comparing a region with rain that is more acidic with another. As can be seen by the above table, the concentration of hydrochloric acid is being manipulated so that the pH value varies by a whole number. ...read more.

Middle

In addition, it should only be handled using appropriate utensils like tongs or tweezers, so as to avoid contaminating the material with hand oils present on human fingers, or other contaminants. It is highly unlikely that pure, distilled water will be available during the investigation due to some presence of impurities. Therefore, the water used in the investigation should come from the same water tank to ensure that at least the contaminants will be somewhat constant throughout the course of the investigation. Materials and Equipment Required for the Investigation: - Stopwatch (seconds, +/- 0.1) - Analytic electronic milligram balance (+/- 0.001g) - 40 cm3 of concentrated 12 mol dm-3 hydrochloric acid (HCl(aq)) - 18 x 50 cm3 (+/- 5 cm3) beakers - 6 x 500 cm3 (+/- 50 cm3) beakers - 1 x 500.0 cm3 (+/- 0.2 cm3) volumetric flask - 12 x 2.00 g strips of sealed zinc metal of equal size (Zn(s)) - 1 x 10.0 cm3 (+/- 0.5 cm3) graduated cylinder - 1 x 50.0 cm3 (+/- 0.5cm3) graduated cylinder - 1 x 100.0cm3 (+/- 0.5cm3) graduated cylinder - Tweezers - Tongs - Electrically powered hot plate - Mercury thermometer (�C, -10 to +110, +/- 0.5) - 12 x Plastic weighing boats - Latex gloves - Safety goggles - Distilled water from the same source - Distilled water bottle pumps from the same source as all distilled water being used - Fume hood lab working station Safety Precautions: - Hydrochloric acid is corrosive, and should be handled with care. Should not come in contact with skin, or be ingested (Sciencelab, 2010). - Zinc is slightly irritant to skin, eyes, and should not be ingested or inhaled. - Safety goggles and latex gloves should be worn at all times during the investigation (Sciencelab, 2010). - Waste products from the all reactions taking place should be disposed of properly, with the assistance of teacher Procedure: Part 1: 1. ...read more.

Conclusion

8. 1 sample of the pre-cut piece of solid zinc metal strip was placed on the weighing boat using tweezers, and on the electronic milligram balance. The mass was recorded to the nearest 0.001g. 9. The piece of solid zinc metal was then placed in the 500cm3 beaker labeled 'Beaker DT1' using tweezers, and a stopwatch was immediately started. Qualitative observations were recorded. 10. Another clean, dry, and empty 50cm3 beaker, labeled 'Beaker DRT1' was massed out on the electronic milligram balance. Its mass was recorded to the nearest 0.001g. 11. After exactly 1 minute had elapsed, the 500cm3 beaker labeled DT1 was decanted of its hydrochloric acid solution, making sure that the zinc metal strip remained. (The solution was decanted into a waste beaker) The remaining zinc was then placed (with the use of tongs) in another clean, and dry 50cm3 beaker that was already massed, labeled 'Beaker DRT1', in which it was washed with distilled water from distilled water bottle pumps. The water was then decanted from the 50cm3 beaker into a waste beaker. 12. The beaker, labeled DRT1, containing the recently rinsed zinc metal strip that reacted with the hydrochloric acid solution for one minute, was then placed on a hot plate set to low heat, and allowed to dry off for 5 minutes. 13. After 5 minutes of heating, the beaker was then set aside, and allowed to cool for 2 minutes, and then placed on the electronic milligram balance. The mass of 'Beaker DRT1' with its sample of dried zinc metal strip that had recently reacted with the hydrochloric acid solution was recorded to the nearest 0.001g. 14. Steps 1-13 were done for two more trials to ensure precision in the data collected. However, the beaker labels for trial two were: DT2/DRT2 and trial three: DT3/DRT3 15. The lab area was cleaned, and hands were washed. Any solid waste remaining was placed in a designated waste container, and any liquid waste was disposed of accordingly. ...read more.

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