Calculate to 2 decimal places, the ratio of base/acid at pH 12. Show all details of your working out. In each step of your working out use the chemical formulas of the compounds that constitute the weak acid and conjugate base. State the final answer in a complete sentence. H2PO4- is the weak acid and HPO42- is the conjugate base.
Question
Calculate to 2 decimal places, the ratio of base/acid at pH 12. Show all details of your working out. In each step of your working out use the chemical formulas of the compounds that constitute the weak acid and conjugate base. State the final answer in a complete sentence. H2PO4- is the weak acid and HPO42- is the conjugate base.
Solution
To calculate the ratio of base/acid at pH 12, we need to use the Henderson-Hasselbalch equation, which is:
pH = pKa + log ([A-]/[HA])
Where:
- pH is the measure of acidity or basicity of the solution.
- pKa is the negative logarithm of the acid dissociation constant (Ka) of the solution.
- [A-] is the molar concentration of the base (in this case, HPO42-).
- [HA] is the molar concentration of the acid (in this case, H2PO4-).
First, we need to know the pKa value for H2PO4-. The pKa value for H2PO4- is 7.2.
Now, we can rearrange the Henderson-Hasselbalch equation to solve for the ratio [A-]/[HA]:
[A-]/[HA] = 10^(pH - pKa)
Substitute the given pH and the pKa value into the equation:
[A-]/[HA] = 10^(12 - 7.2)
[A-]/[HA] = 10^4.8
[A-]/[HA] = 63,095.73444801933
Rounding to two decimal places, the ratio of HPO42- (base) to H2PO4- (acid) at pH 12 is 63,095.73.
So, the final answer is: The ratio of the base HPO42- to the acid H2PO4- at pH 12 is 63,095.73 to 1.
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