Ammonia Reactions

Question 1

Series of reactions between Cr3+ metal aqua ion and NH3/excess

Answer 1

With NH3:
Cr(OH)3(H2O)3 green precip
With excess:
[Cr(NH3)6] 3+ purple solution

Question 2

Series of reactions between Fe2+ metal aqua ion and NH3/excess

Answer 2

With NH3:
Green precip of Fe(OH)2(H2O)4
-no change with excess

Question 3

Series of reactions between Fe3+ metal aqua ion and NH3/excess

Answer 3

With NH3:
Brown precip of Fe(H2O)3(OH)3
-no change with excess

Question 4

Series of reactions between Co2+ metal aqua ion and NH3/excess and on standing

Answer 4

With NH3:
Blue precip of Co(OH)2(H2O)4
With excess:
[Co(NH3)6]2+ yellow solution which gradually darkens as oxidised to [Co(NH3)6]3+

Question 5

Series of reactions between Cu2+ metal aqua ion and NH3/excess

Answer 5

With NH3:
Blue precip of Cu(OH)2(H2O)4
With excess:
Dark blue solution of [Cu(NH3)4(H2O)2]2+

Question 6

What is the number of OH- substituted the same as not with excess

Answer 6

The value of the charge on the initial ion

Question 7

How does chromium hydroxide precip react with acid

Answer 7

Like all hydroxides
Accepts three protons which protonate OH- ligands to form [Cr(H2O)6]3+

Question 8

How does chromium hydroxide precipitate react with base

Answer 8

OH- ions accept protons from three water ligands to form [Cr(OH)6]3- and 3H2O

Question 9

Why can water ligands be deprotonated in +3 metal ion complexes

Answer 9

As the +3 are polarising due to small size and high charge so high electron density so polarise O-H bond to greater extent which weakens it and means it is more likely to break and proton accepted by base

Question 10

Why is Fe3+ more acidic than Fe2+

Answer 10

Because the Fe3+ ion has a higher charge density due to greater charge for same size so more polarising, weakens O-H bond to a greater extent meaning H2O able to accept proton that ligand has released into solution

Question 11

What state is the ammonia in

Answer 11

Aqueous