Which Acid is Stronger: HCN or Phosphoric Acid?
Based on the data, which acid is stronger, and by what degree?
a) HCN is 7.2 times more acidic
b) HCN is approximately 10,000,000 times more acidic
c) Phosphoric acid is 7.2 times more acidic
d) Phosphoric acid is approximately 10,000,000 times more acidic
Answer:
Phosphoric acid, with its pKa of 2.1, is approximately 10,000,000 times stronger than HCN, which has a pKa of 9.3. The correct answer is d) Phosphoric acid is approximately 10,000,000 times more acidic.
The strength of an acid is determined by its pKa value; the lower the pKa, the stronger the acid. Phosphoric acid has a pKa value of 2.1, compared to HCN which has a pKa value of 9.3. To determine how much stronger one acid is compared to another, we need to look at the difference in pKa values. Given the pKa values for phosphoric acid and HCN, we calculate 10 to the power of the difference in pKa values (which is 9.3 - 2.1 = 7.2). Antilog(7.2) = 10^7.2 which is approximately 10,000,000 times. Therefore, phosphoric acid is roughly 10,000,000 times stronger than HCN.