A2- Reactions in Aqueous Solution

Question 1

What is the colour of [Fe(H2O)6]2+ (aq)?

Answer 1

green solution

Question 2

What are the observations when NaOH/dilute NH3 is added to aqueous Fe2+?

Answer 2

• green ppt goes brown on standing in air

Question 3

What colour is FeCO3(s)?
When is it formed?

Answer 3

• green ppt
• action of Na2CO3(aq)

Question 4

What is the colour of [Cu(H2O)6]2+ (aq)?

Answer 4

blue solution

Question 5

What are the observations when NaOH/dilute NH3 is added to aqueous Cu2+?

Answer 5

• blue ppt

Question 6

What is formed when aqueous Cu2+ reacts with an excess of concentrated ammonia?

Answer 6

[Cu(H2O)2(NH3)4]2+ (aq)
deep/royal blue solution

Question 7

What colour is CuCO3(s)? When is it formed?

Answer 7

• blue-green ppt
• action of Na2CO3 (aq)

Question 8

What colour is [CuCl4]2+?

Answer 8

green

Question 9

What colour is [Fe(H2O)6]3+ (aq)?

Answer 9

purple solution
may look yellow-brown due to presence of some Fe(H2O)3(OH)3 (s)

Question 10

What are the observations when NaOH/dilute NH3 is added to aqueous Fe3+?

Answer 10

• brown ppt

Question 11

What colour is [Al(H2O)6]3+ (aq)?

Answer 11

colourless solution

Question 12

What are the observations when NaOH/dilute NH3 is added to aqueous Al3+?

Answer 12

• white ppt

Question 13

What happens when excess of NaOH is reacted with Aluminium (III)?

Answer 13

[Al(OH)4(H2O)2]- (aq)
white ppt redissolves
colourless solution

Question 14

Why are aqueous metal ions acidic?

Answer 14

• metal ion is polarising
• attracts electron density off of the water ligands
• weakens O-H bond (allows H+ to be donated)

Question 15

Why is Al3+ more acidic than Fe3+?

Answer 15

Al3+ is smaller
greater charge density
so greater polarising power
so O-H can be deprotonated easier

Question 16

Why are 3+ ions more acidic than 2+ ions?

Answer 16

greater charge
so more polarising
so O-H can be deprotonated easier

Question 17

What is the end product formed when aqueous Al3+ react with excess NaOH?

Answer 17

[Al(H2O)2(OH)4]-

Question 18

Why are the end products (when reacted in excess) different in the reactions with NH3 and NaOH?

Answer 18

NaOH is a stronger base, whereas NH3 is not a strong enough base to further deprotonate

Question 19

Give the 3 bases involved in these reactions in order of their strength…

Answer 19

OH- > NH3 > CO32-

Question 20

What does NaCO3 deprotonate?

Answer 20

M3+ ions

Question 21

What equation shows the action of NaCO3 reacting with aqua-metal 3+ ions?

Answer 21

2[M(H2O)6]3+ + 3CO32- –> 2M(H2O)3(OH)3 + 3H2O + 3CO2

Question 22

What observation is made when M3+ ions react with NaCO3?

Answer 22

bubbles/effervescence due to CO2
colour change dependent on ion

Question 23

Why do M2+ ions not form a metal hydroxide ppt when they react with NaCO3?

Answer 23

too weak and acid to react with the weak base NaCO3

Question 24

What equation shows the reaction of NaCO3 and aqueous M2+ ions?

Answer 24

[M(H2O)6]2+ + CO32- –> MCO3 + 6H2O

Question 25

What colour is FeCO3(s)?

Answer 25

green ppt

Question 26

Why does Aluminium form a colourless solution?

Answer 26

does not have an incomplete d-subshell