Ammonia forms the complex ion [Cu(NH3)4]2+ion with copper ions in alkaline solutions but not in acidic solution. What is the reason for it – [AIEEE-2003]a)In acidic solution hydration protects copper ionsb)In acidic solutions protons coordinate with ammonia molecules forming NH4+ions and NH3molecules are not availablec)In alkaline solutions insoluble Cu(OH)2is precipitated which is soluble in excess of any alkalid)Copper hydroxide is an amphoteric substanceCorrect answer is option 'B'. Can you explain this answer?

Question

Ammonia forms the complex ion [Cu(NH3)4]2+ion with copper ions in alkaline solutions but not in acidic solution. What is the reason for it &ndash;                     [AIEEE-2003]a)In acidic solution hydration protects copper ionsb)In acidic solutions protons coordinate with ammonia molecules forming NH4+ions and NH3molecules are not availablec)In alkaline solutions insoluble Cu(OH)2is precipitated which is soluble in excess of any alkalid)Copper hydroxide is an amphoteric substanceCorrect answer is option 'B'. Can you explain this answer?

Answer

Well, it's because Ammonia being a Lewis base will react with the acidic medium to form a salt instead

Answer

The reason for the formation of the complex ion [Cu(NH3)4]2+ in alkaline solutions but not in acidic solutions is due to the difference in pH.

In alkaline solutions, the concentration of hydroxide ions (OH-) is high. The presence of hydroxide ions can deprotonate the ammonia (NH3) molecules, forming ammonium ions (NH4+). The ammonium ions can then coordinate with the copper ions (Cu2+), forming the complex ion [Cu(NH3)4]2+.

On the other hand, in acidic solutions, the concentration of hydrogen ions (H+) is high. The presence of hydrogen ions can protonate the ammonia (NH3) molecules, converting them into ammonium ions (NH4+). The ammonium ions cannot coordinate with the copper ions (Cu2+) to form the complex ion [Cu(NH3)4]2+.

Therefore, the pH of the solution plays a crucial role in determining whether the complex ion [Cu(NH3)4]2+ can form or not.

Answer

The correct answer is option B
In acidic solutions, ammonia reacts with proton and forms ammonium ion which further cannot act as a ligand. Also, no free ammonia molecules are available for co-ordination. Hence, it does not form a complex with copper ion.
The reaction is as follows:
NH₃ + H⁺ → NH₄⁺

Answer

The correct answer is option B
In acidic solutions, ammonia reacts with proton and forms ammonium ion which further cannot act as a ligand. Also, no free ammonia molecules are available for co-ordination. Hence, it does not form a complex with copper ion.
The reaction is as follows:
NH₃ + H⁺ → NH₄⁺

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