Question

What is the component concentration ratio, [no2−]/[hno2], of a buffer that has a ph of 3.90? (ka of hno2 = 7.1 × 10−4)?

Answer 1

According to Henderson–Hasselbalch Equation,

pH = pKa + log [Nitrate] / [Nitric Acid]

As, Ka of Nitric Acid = 7.1 × 10⁻⁴
So,
pKa = -log [ 7.1 × 10⁻⁴ ]

pKa = 3.148

So, pH = 3.148 + log [Nitrate] / [Nitric Acid]

3.90 = 3.148 + log [Nitrate] / [Nitric Acid]

3.90 - 3.148 = log [Nitrate] / [Nitric Acid]

0.752 = log [Nitrate] / [Nitric Acid]

Taking Antilog on both sides,

[Nitrate] / [Nitric Acid] = 5.64