JEE Advanced · Polyprotic · n-Factor · Buffer · Henderson–Hasselbalch
Yes. If $[H^+] > 1\text{ M}$ (e.g., concentrated $HCl$), pH becomes negative. At 10 M HCl, pH ≈ –1.
H₂SO₄ is diprotic so n = 2. A 0.5 M H₂SO₄ solution delivers $[H^+] = 1.0\text{ M}$, giving pH = 0.
When $C/Ka < 100$, i.e., concentration is low relative to Ka. In this case the approximation $x \ll C$ fails and the full ICE quadratic $x^2 + Kax – KaC = 0$ must be solved.
As temperature rises, $K_w$ increases, so the neutral point drops below 7. At 37°C (body temp), neutral pH ≈ 6.82.
Applies only when $[HA]/[A^-]$ ratio is between 0.1 and 10 (i.e., pH within ±1 of pKa). At extremes the approximation breaks down.
$K_w = [H^+][OH^-] = 10^{-14}$ at 25°C. Endothermic reaction — rising temperature increases $K_w$.