Acids/Bases Design Lab. 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

2. Pressure is also a factor that can affect the rate at which two reactants chemically react. At higher pressures, the rate of reaction between hydrochloric acid and zinc metal would increase (WebChem, n.d.).

It is important to control the pressure in order to mitigate it’s effects on the investigation, since a higher pressure in one trial would then adversely impact the resulting yield of the remaining zinc metal after 1 minute because at higher pressures, reactants are closer together and therefore have more opportunity to collide with other substances – namely the reactant, and this would therefore increase the rate of reaction.

This variable will be controlled by having the investigation conducted beneath a fume hood, since the pressure in that small area will most probably be the same, and this also allows for the hydrogen gas that is produced to be safely collected. Therefore, the impact of pressure, as a variable in the investigation, is severely mitigated and will have virtually no/negligible impact on the data collected from the investigation.

3. The physical state is a significant factor affecting the rate of reaction (WebChem, n.d.). Meaning, if one reactant is granular, for example, it will react much quicker than a reactant that is in large, solid chunks, since the substance it is reacting with will have more opportunities to interact with the particles of the reactant.

This is a significant variable to control because if different physical states were used throughout the investigation, the results would be invalid. If one trial uses mossy zinc chunks as the zinc metal reactant, and the other uses zinc metal strips, the results will be quite different due to the fact that the two have different surface areas and therefore more/less opportunity to react.

This variable will be controlled by ensuring the hydrochloric acid is of course in aqueous form, and that the zinc metal strips used are kept at approximately the same size. This means, a zinc strip weighing no less than 2.00 grams will be used in the investigation for each variation of concentration of hydrochloric acid, and for each of the subsequent trials, and the dimensions of the zinc strips should be as similar as possible to limit the effects of the size of the reactants on the rate of reaction.  

4. The time of the reaction taking place between a solid strip of zinc metal, and the varying concentrations of hydrochloric acid solution must be controlled.

This is important because for some of the concentrations of hydrochloric acid being used, the zinc metal strips are very slightly in excess, as will be discussed at further length in the appendix section of this investigation. This means that at precisely one minute, the hydrochloric acid solution must be emptied from the beaker containing the reaction between it, and the zinc metal strip, and rinsed with distilled water. Any extra time allotted will mean more of the zinc metal will have reacted to form aqueous zinc chloride, and will thus not be included in the final mass of the unreacted zinc metal taken (the dependent variable).

Therefore, a stopwatch will be needed to ensure that proper timing is executed throughout the investigation. It will be used to indicate exactly when one minute has elapsed since the introduction of the zinc metal strip to the hydrochloric acid, at which point the hydrochloric acid solution can be decanted out, and the zinc metal strip retrieved, rinsed with distilled water, heated, and massed.

5. For each concentration of hydrochloric acid being used in the investigation (2 mol dm-3,, 1 mol dm-3, 0.1 mol dm-3, and 0.01 mol dm-3), the three trials conducted for each must contain the same volume to ensure that the concentration of the hydrochloric acid, and, in extension, H+ ions, are present in equimolar quantities across the three trials.

This is important to ensure that within each variation of the concentration of hydrochloric acid that the volume is the same because if the volume is slightly different, the concentration of hydrochloric acid will then fluctuate, and therefore the pH will not be consistent across the three trials. For example, if in one of the trials using 2 mol dm-3 hydrochloric acid, one of the samples contains 0.029 dm3, the concentration of the hydrochloric acid then increases to 2.068, and therefore, the pH value will also increase. This could potentially compromise experimental data collected during the investigation.

To control this variable throughout the investigation, the following table must be explicitly followed. Unlike other investigations where some discrepancy is allowed, it is imperative that the appropriate quantities are present to ensure that an accurate rate of reaction can be measured.

6. The purity of reactants must be considered as a variable requiring control during the investigation, namely, the distilled water, which the concentrated hydrochloric acid is being added to, and the zinc metal strips.

It is important to ensure that the zinc metal strips are exposed to the air as little as possible before it is massed on the electronic milligram balance (+/- 0.001g) and reacted with the solution of hydrochloric acid, since it oxidizes and forms a protective layer of zinc oxide (Gagnon, n.d.). This could add extra mass to what is believed to be solely zinc metal that is being massed on the electronic milligram balance.

On the other hand, the distilled water being used, and with which the concentrated hydrochloric acid will combine with to form the necessary concentrations of hydrochloric acid solution, could contain some impurities like dissolved carbon dioxide. If some of the distilled water is acquired from different water tanks, or was distilled at different times, they could have varying amounts of dissolved impurities.

Therefore, to prevent the oxidizing of the zinc metal strips, they should be kept in the protective packaging which they were received in from the manufacturer for as long as possible to mitigate the effects of zinc oxidizing. Only when needed to be massed, and just before the reaction, should the zinc be exposed to the air. 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. Safety goggles and latex gloves were worn.
2. The procedure was performed beneath a fume hood.
3. A clean, dry 10.0cm3 graduated cylinder was filled with precisely 2.0 cm3 of distilled water. Then, 5.0cm3 of the concentrated 12 mol dm-3 hydrochloric acid was added to the 2.0cm3 of distilled water, making 7.0cm3.  (Recall: do as you otter, add acid to water!)
4. A clean, dry, 50.0cm3 graduated cylinder was filled with approximately 10.0cm3 of distilled water. The 7.0cm3 of hydrochloric acid solution in the 10.0cm3 graduated cylinder, was then added to the 50.0cm3 graduated cylinder containing approximately 10.0cm3 of distilled water.
5. The 50.0cm3 graduated cylinder, now containing approximately 17.0cm3 of hydrochloric acid solution, was filled with distilled water until the volume read 30.0cm3. Record the volume measured of the hydrochloric acid solution contained in the 50.0 cm3 graduated cylinder.
6. The hydrochloric acid solution in the 50.0cm3 graduated cylinder, was emptied into a 50cm3 beaker. This beaker was labeled ‘Beaker AT1’, and a mercury thermometer was inserted inside the solution, and the temperature was recorded.
7. A clean, and dry weighing boat was placed on the electronic milligram balance (+/- 0.001g), and its mass was recorded to the nearest 0.001g.
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 50cm3 beaker labeled Beaker AT1 using tweezers, and a stopwatch was started immediately. Qualitative observations were recorded.
10. Another clean, dry, and empty 50cm3 beaker, labeled ‘Beaker ART1’ was massed out on the electronic milligram balance. Its mass was recorded to the nearest 0.001g.
11. After exactly 1 minute has elapsed, the 50cm3 beaker labeled AT1 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 ART1’, 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 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 ART1’ 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: AT2/ART2 and trial three: AT3/ART3
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.

Part 2:

1. Safety goggles and latex gloves were worn.
2. The procedure was performed beneath a fume hood.
3. A clean, dry 10.0cm3 graduated cylinder was filled with precisely 2.0 cm3 of distilled water. Then, 4.2cm3 of the concentrated 12 mol dm-3 hydrochloric acid was added to the 2.0cm3 of distilled water, making 6.2cm3.  (Recall, do as you otter, add acid to water!)
4. A clean, dry, 50.0cm3 graduated cylinder was filled with approximately 10.0cm3 of distilled water. The 6.2cm3 of hydrochloric acid solution in the 10.0cm3 graduated cylinder, was then added to the 50.0cm3 graduated cylinder containing approximately 10.0cm3 of distilled water.
5. The 50.0cm3 graduated cylinder, now containing approximately 16.2cm3 of hydrochloric acid solution, was filled with distilled water until the volume read 50.0cm3. The volume of the hydrochloric acid solution contained in the 50.0 cm3 graduated cylinder was recorded.
6. The hydrochloric acid solution in the 50.0cm3 graduated cylinder, was emptied into a 50cm3 beaker. This beaker was labeled ‘Beaker BT1’, and a mercury thermometer was inserted inside the solution, and the temperature was recorded.
7. A clean, and dry weighing boat was placed on the electronic milligram balance (+/- 0.001g), and its mass was recorded to the nearest 0.001g.
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 50cm3 beaker labeled ‘Beaker BT1’ using tweezers, and a stopwatch was immediately started. Qualitative observations were recorded.
10. Another clean, dry, and empty 50cm3 beaker, labeled ‘Beaker BRT1’ was massed out on the electronic milligram balance. Its mass was recorded to the nearest 0.001g.
11. After exactly 1 minute has elapsed, the 50cm3 beaker labeled BT1 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 BRT1’, 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 BRT1, 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 BRT1’ 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: BT2/BRT2 and trial three: BT3/BRT3
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.

Part 3:

1. Safety goggles and latex gloves were worn.
2. The procedure was performed beneath a fume hood.
3. A clean, dry 10.0cm3 graduated cylinder was filled with precisely 2.0 cm3 of distilled water. Then, 2.5cm3 of the concentrated 12 mol dm-3 hydrochloric acid was added to the 2.0cm3 of distilled water, making 4.5cm3.  (Recall, do as you otter, add acid to water!)
4. A clean, dry, 50.0cm3 graduated cylinder was filled with approximately 10.0cm3 of distilled water. The 4.5cm3 of hydrochloric acid solution in the 10.0cm3 graduated cylinder, was then added to the 50.0cm3 graduated cylinder containing approximately 10.0cm3 of distilled water.
5. The 50.0cm3 graduated cylinder, now containing approximately 14.5cm3 of hydrochloric acid solution, was filled with distilled water until the volume read 50.0cm3. The volume of the hydrochloric acid solution contained in the 50.0 cm3 graduated cylinder was recorded.
6. The hydrochloric acid solution in the 50.0cm3 graduated cylinder, was emptied into a 500cm3 beaker. This beaker was labeled ‘Beaker CT1’, and a mercury thermometer was inserted inside the solution, and the temperature was recorded.
7. A 100.0cm3 graduated cylinder was used to add 150.0cm3 of distilled water to the 500cm3 beaker labeled ‘Beaker CT1’ (Once of 100.0cm3, then 50.0cm3)
8. A clean, and dry weighing boat was placed on the electronic milligram balance (+/- 0.001g), and its mass was recorded to the nearest 0.001g.
9. 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.
10. The piece of solid zinc metal was then placed in the 500cm3 beaker labeled ‘Beaker BT1’, containing the hydrochloric acid solution, using tweezers, and a stopwatch was immediately started. Qualitative observations were recorded.
11. Another clean, dry, and empty 50cm3 beaker, labeled ‘Beaker CRT1’ was massed out on the electronic milligram balance. Its mass was recorded to the nearest 0.001g.
12. After exactly 1 minute has elapsed, the 500cm3 beaker labeled CT1 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 CRT1’, in which it was washed with distilled water from distilled water bottle pumps. The water was then decanted from the 500cm3 beaker into a waste beaker.
13. The beaker, labeled CRT1, 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.
14. 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 CRT1’ with its sample of dried zinc metal strip that had recently reacted with the hydrochloric acid solution was recorded to the nearest 0.001g.
15. Steps 1-13 were done for two more trials to ensure precision in the data collected. However, the beaker labels for trial two were: CT2/CRT2 and trial three: CT3/CRT3
16. 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.

Part 4:

1. Safety goggles and latex gloves were worn.
2. The procedure was performed beneath a fume hood.
3. A clean, dry 10.0cm3 graduated cylinder was filled with precisely 2.0 cm3 of distilled water. Then, 0.4 cm3 of the concentrated 12 mol dm-3 hydrochloric acid was added to the 2.0cm3 of distilled water, making 2.4 cm3.  (Recall, do as you otter, add acid to water!)
4. A clean, dry, 500.0 cm3 volumetric flask was filled approximately halfway with distilled water. The 2.4cm3 of hydrochloric acid solution in the 10.0cm3 graduated cylinder, was then added to the 500.0 cm3 volumetric flask containing approximately 250.0 cm3 of distilled water
5. The 500.0 cm3 volumetric flask now contained approximately 257.4 cm3 of hydrochloric acid solution. The 500.0 cm3 volumetric flask was then filled completely with distilled water, so that the final volume read 500.0cm3.
6. The hydrochloric acid solution in the 500.0 cm3 volumetric flask was emptied into a 500cm3 beaker. This beaker was labeled ‘Beaker DT1’, and a mercury thermometer was inserted inside the solution, and the temperature was recorded.
7. A clean, and dry weighing boat was placed on the electronic milligram balance (+/- 0.001g), and its mass was recorded to the nearest 0.001g.
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.

Works Cited

"4.4.24.1  Reaction of Metals with Hydrochloric Acid   ." Universität Siegen: Zukunft menschlich gestalten | Universität Siegen. N.p., n.d. Web. 26 Feb. 2012. <http://www2.uni-siegen.de/~pci/versuche/english/v44-24-1.html>.

"Factors that Affect Rate of Reaction." WebChem. N.p., n.d. Web. 25 Feb. 2012. <www.webchem.net/notes/how_far/kinetics/rate_factors.htm>.

Gagnon, Steve. "It's Elemental - The Element Zinc." Science Education at Jefferson Lab. N.p., n.d. Web. 26 Feb. 2012. <http://education.jlab.org/itselemental/ele030.html>.

Helmenstine,  Anne Marie. "Factors that Affect the Chemical Reaction Rate - Reaction Kinetics." Chemistry - Periodic Table, Chemistry Projects, and Chemistry Homework Help. N.p., n.d. Web. 25 Feb. 2012. <http://chemistry.about.com/od/stoichiometry/a/reactionrate.htm>.

Sciencelab. "Material Safety Data Sheet Zinc." Sciencelab. N.p., n.d. Web. 26 Feb. 2012. <www.sciencelab.com/msds.php?msdsId=9925476>.

Sciencelab. "MSDS Hydrochloric Acid." Sciencelab. N.p., n.d. Web. 25 Feb. 2012. <www.sciencelab.com/msds.php?msdsId=9924285>.