Weak polyprotic acids are normally
added to Coca Cola to lower its pH
to about 2.5 and impart tartness?
Show that a two litter cocacola
bottled drink that contains 0.057 to
0.084 percent of 75 percent of
phosphoric acid by mass,meets this
ph requirement.
Pka1= 2.12
To determine if a two-liter Coca Cola drink with a certain concentration of phosphoric acid meets the desired pH requirement, we need to calculate the concentration of the acid and relate it to its dissociation constants.
First, let's calculate the mass of phosphoric acid in the drink. We are given that the drink contains 0.057 to 0.084 percent of 75 percent of the acid by mass. Since the purity of phosphoric acid is 75 percent, we can calculate the mass as follows:
Mass of phosphoric acid = (0.057% to 0.084%) * 75% * mass of the drink
Next, we need to calculate the molar concentration of phosphoric acid using the mass calculated above. To do this, we need the molar mass of phosphoric acid.
Phosphoric acid (H₃PO₄) has a molar mass of:
(1 * atomic mass of H) + (3 * atomic mass of O) + (1 * atomic mass of P)
From the periodic table:
Atomic mass of H = 1 g/mol
Atomic mass of O = 16 g/mol
Atomic mass of P = 31 g/mol
Now, we can calculate the molar mass of phosphoric acid.
Molar mass of H₃PO₄ = (1 * 3) + (16 * 4) + 31 = 98 g/mol
Using the molar mass, we can calculate the molar concentration (in mol/L or M) of phosphoric acid:
Molar concentration = (mass of phosphoric acid) / (molar mass of H₃PO₄) / (volume of the drink)
Assuming a two-liter drink, the volume of the drink would be 2.0 L. Substituting the given values, we can now calculate the molar concentration.
Once we have the molar concentration of phosphoric acid, we can use the Henderson-Hasselbalch equation to determine the pH. The Henderson-Hasselbalch equation for a weak acid is:
pH = pKa + log ([A-] / [HA])
Given that pKa1 of phosphoric acid is 2.12, we can use this equation to find the pH.
Here's a step-by-step outline of the solution:
1. Calculate the mass of phosphoric acid in the drink using the given percentage and volume.
2. Calculate the molar concentration of phosphoric acid using the mass and molar mass.
3. Use the Henderson-Hasselbalch equation to find the pH, substituting the calculated molar concentration and pKa1.
By following these steps, you can determine if a two-liter Coca Cola drink with a certain concentration of phosphoric acid meets the desired pH requirement of approximately 2.5.