1
Which statement is wrong about pH and H+?
- pH of neutral water is not zero.
- Adding 1 N solution of CH3COOH and 1 N solution of NaOH, pH will be seven.
- [H+] of dilute and hot H2SO4 is more than concentrated and cold H2SO4
- Mixing solution of CH3COOH and HCl. pH will be less than 7.
Answer
(2) Adding 1 N solution of CH3COOH and 1 N solution of NaOH, pH will be seven.
Solution
(1) Neutral water at 298 K has pH = 7, not zero — correct.
(2) Equal equivalents of CH3COOH and NaOH give CH3COONa, a salt of a weak acid and a strong base.
As per NCERT, such a salt undergoes hydrolysis: CH3COO- + H2O CH3COOH + OH-
⇒ the solution is basic, pH > 7. So statement (2) is wrong.
(3) Concentrated H2SO4 contains very little water and is only slightly ionised; dilute H2SO4 is almost completely ionised and ionisation increases on heating ⇒ more [H+] — correct.
(4) A mixture of two acids is acidic, pH < 7 — correct.
Answer: (2)
AIPMT 2000