Question

Which of the following reagents, when added in excess to a saturated solution of ZnCO₃, would cause more of the solid zinc carbonate to dissolve?

i) 6 M NaOH

                        ii) 6 M HCl

                        iii) 6 M NH₃

A) i only          B) ii only         C) iii only        D) i and ii            E) ii and iii      F) i and iii     G) i, ii, and iii

Answer: G Please explain why, thank you !!

Answer 1

ZnCO₃ is soluble in 6M HCl, 6M NaOH & 6 M NH₃ as per following Equation:

1)ZnCO₃ +HCl -------> ZnCl_{2 aq} + H₂O + CO_{2 (g)}

2)ZnCO₃ + 2NaOH -------> Zn(OH)₂ (s) + H₂O + CO_2(g)

Zn(OH)₂ (s) + 2 ^-OH _(aq.) ------>[Zn(OH)₄]^2- aq. soluble complex is formed with 6M NaOH

3) ZnCO₃   + 2NaOH -------> Zn(OH)₂ (s) + H₂O + CO_2(g)

Zn(OH)₂ (s) + 4NH_{3 (aq.)}   ------>[Zn(NH3)₄] ^2- aq. soluble complex is formed with 6M NH3

+2^-OH

Therefore answer G. I,II &III is correct.