Tonic Water

CONCLUSION

In the titration of tonic water with the strong base sodium hydroxide, it was determined that tonic water contains a buffer. Qualitatively, this is evident by the region of relatively stable pH on the titration curve before the equivalence point. Tonic water contains a buffer, meaning that the solution resists changes in its pH in accordance to its buffering capacity, which is greatest over the effective buffering range.

The equivalence point of this titration was determined by finding the part of the titration curve with this steepest slope. At this point, the concentrations of [OH-] and [H+] are equivalent. For the titration of tonic water with sodium hydroxide, this point occurs at 16.0mL of NaOH added and a pH of 8.83, as determined from the titration curve. It is reasonable that this titration has a basic equivalence point, considering that NaOH is known to be a strong base, and tonic water had an initial pH of 2.74, indicating that it is a weak acid. Thus, as the titration progresses, a strong conjugate base and a weak conjugate acid will be formed, leading to a basic equivalence point. Furthermore, in this titration, a basic salt is formed. This basic salt will be composed of a cation from the strong base (Na) and the anion from the weak acid (HCO3- ). Sodium bicarbonate (NaHCO3) is formed.

Since the equivalence point occurs when 16.0 mL of NaOH are added, the pKa, or half- equivalence point will equal the pH when half of the acid is neutralized, at 8.0mL NaOH added. The pKa for the buffer is therefore 5.05. Thus, the effective buffering range for the buffer in tonic water is 4.05 to 6.05. In this interval of pH, the buffering capacity of tonic water is the greatest. This means that the buffer resists changes to its pH best during this range. The formula of tonic water is H2CO3 . Accordingly, a possible buffer system could be H2CO3 /HCO3- . This buffer system includes a weak acid and its conjugate base. Upon observing the titration curve, it is clear that there is a buffering region, but this region is not necessarily as apparent as it ought to be. This could possibly be due to the dilute nature of both the acid and the base. Sodium hydroxide was 0.1 M, and the tonic water includes other components as well as bicarbonate. Therefore, if the acid and the base had been more concentrated, the buffering region would have been more obvious on the titration curve. As mentioned in the background information, buffers work best when there are large quantities of both acid and base.

As for the practical application, it is crucial that tonic water contains a buffer. The human body must remain at a stable pH in order for all the enzymes to function correctly. This is why blood must be a buffer. Tonic water is consumed, and therefore its pH must be resistant to change in order for it to be safe for humans to drink. Therefore, tonic water contains a buffer.

Gatorade

Resulting Implications

Buffers are crucial when trying to keep environments with delicate pH ranges in check, for certain vital enzymes in the system only work at a precise pH range; if the pH shifts out of the specified range, the enzymes slow down, or even stop and denature. One example of a buffer is the mixture of carbonic acid and bicarbonate, present in blood plasma in order to maintain a very narrow pH range of 7.35 and 7.45. Buffers are also used in industry, where they can increase a drug’s shelf-life, maintain a drug’s pH level to neutral so as not to harm humans, and protect a drug against unintended hydrolysis in aqueous solutions. Another industry that is highly reliant on buffers is the fermentation industry. Fermentation reactions, such as in bread and yogurt, mandate specific pH ranges, and in order to achieve this, buffers are utilized. The textile and leather industry also use buffers to obtain the desired dye colors for their fabrics, and even the manufacturing of glue requires buffers to keep gelatin, a component of glue, inside a narrow pH.

The titration of Gatorade with 0.1 M sodium hydroxide revealed that Gatorade does indeed contain the buffering components citric acid and its conjugate base because the Gatorade resisted changes in pH very well leading up to the equivalence point of the titration.

The titration curve of Gatorade clearly exhibits the shape of a weak acid/strong base titration curve, with a basic equivalence point and a longer buffering region leading up to the equivalence point. The equivalence point occurs when 6.5 mL of 0.1 M NaOH were added, leading the moles of NaOH and moles of weak acid in the Gatorade to be equal at an approximate pH of 8.40. This slightly basic equivalence point proves that Gatorade contains weak acids because the equivalence point of a titration can only be basic if a basic salt is formed at that point from what must be the strong conjugate base of the (weak) acidic components of Gatorade and the neutral cation from NaOH. It stands to reason that since Gatorade is a weak acid, it has a buffer system within. The titration curve of Gatorade with NaOH further solidifies the idea that Gatorade contains buffer components. Because there is a clear buffering region on the curve between the beginning of the titration and the equivalence point where the pH changes minimally with each addition of NaOH, it stands to reason that there is a buffer system-- a mixture of weak acid and strong conjugate base anions-- in the Gatorade that allows the solution to resist a change in pH with such ease in this pH range.

The pKa value for the titration of Gatorade is approximately 5.00, occurring at the half-equivalence point when approximately 3.25 mL of NaOH have been added. The buffering range of any effective buffer components within the Gatorade must therefore be from a pH of 4.00 to 6.00, where the buffering capacity of the Gatorade is the greatest, as demonstrated by the minimal changes in pH on the titration curve while the pH of the Gatorade-NaOH solution was in this range. Gatorade contains two components that could possibly act as buffers: citric acid and monopotassium phosphate. Based on the introductory activity data, the equivalence point for the titration of citric acid with NaOH occurs when 12 mL of NaOH have been added; thus, the half-equivalence point occurs when 6.0 mL of NaOH have been added, at a pH of approximately 4.00. Consequently, the experimentally determined pKa of citric acid is 4.00 and the effective buffering range of citric acid is from 3.00 to 5.00. This matches the buffering range exhibited by Gatorade in the titration of Gatorade with NaOH nearly perfectly, implying that citric acid is the principal buffer component in Gatorade. What does this imply about the role of monopotassium phosphate? The effective buffering ranges of monopotassium phosphate, which is polyprotic and thus has two equivalence points, are from 1.10 to 3.10 and from 6.21 to 8.21. Neither of these pH ranges match the buffering ranges on the Gatorade titration curve; in other words, monopotassium phosphate is not a significant buffer component of Gatorade. This is likely due to the fact that the concentrations of monopotassium phosphate and its conjugate base are not high enough for the buffer system to act effectively-- the ideal buffer system has high concentrations of buffer component relative to the hydronium and hydroxide ion concentrations, as mentioned in the introduction-- and thus the Gatorade is incapable of resisting pH changes as effectively in the would-be buffering ranges of monopotassium phosphate.

It is important for chemists to understand the concept of buffer solutions in relation to sports drinks like Gatorade because the vitamins, sugars, and flavors added to these drinks often make the beverage very acidic. Without the addition of a buffering component, Gatorade would be too dangerous to drink, as ingesting the liquid would elicit an increase in the pH of crucial body fluids such as blood, effectively denaturing the enzymes in the body and hobbling metabolic processes in the cells. To prevent this horrendous effect, manufacturers include buffering components in sports drinks like Gatorade.