CHEMISTRY

JAMB 2006 - Question 9

Chemistry 2006 JAMB Past Questions - Question 9: The ion that will give a white precipitate with aqueous NaOH and soluble in excess of the base is

Choose the correct answers from the options given.
The ion that will give a white precipitate with aqueous NaOH and soluble in excess of the base is
A:
B:
C:
D:
Examkits App

Examkit's JAMB CBT App

Practice JAMB offline with our Online, PC and Mobile App

  • ✅ 25+ years of past questions (2000 to 2025)
  • ✅ Video solutions and explanation to questions
  • ✅ E-library
  • ✅ Study by topic
  • ✅ And more.

Correct Answer

C

Explanation

The ion that will give a white precipitate with aqueous NaOH and is soluble in excess of the base is zinc ion (Zn²+). When zinc ion reacts with aqueous sodium hydroxide (NaOH), it forms a white precipitate of zinc hydroxide (Zn(OH)₂). However, this precipitate is soluble in excess sodium hydroxide, forming a colorless solution of zincate ions:

Zn²+ + 2NaOH → Zn(OH)₂ (white precipitate)
Zn(OH)₂ + 2NaOH → [Zn(OH)₄]²⁻ (soluble complex)

In contrast, calcium ion (Ca²+), magnesium ion (Mg²+), and copper ion (Cu²+) form insoluble hydroxide precipitates with sodium hydroxide that do not dissolve in excess base.