Chem5 - Transition Metals - Chromium

Question 0

Describe and explain what happens when you add warm hydrogen peroxide in alkaline conditions to [Cr(H2O)6]^3+ (3)

Answer 0

~from a green solution
~to a yellow solution
~as [Cr(H2O)6]^3+ is oxidised to CrO4^2-

Question 1

Describe and explain what happens when acidified potassium dichromate has Zinc and HCl added to it? (3)

Answer 1

~colour change from an orange solution
~to a green solution
~as Cr2O7^2- is reduced to [Cr(H2O)6]^3+

Question 2

Describe and explain what happens when acidified potassium dichromate is put in alkaline conditions (3)

Answer 2

~goes from orange solution
~to a yellow solution
~H2O + Cr2O7^2- –> 2CrO4^2- + 2H+ (Goes from dichromate to chromate)

Question 3

Describe and explain what happens when you add warm hydrogen peroxide in alkaline conditions to [Cr(OH)6]^3- (4)

Answer 3

~from a green solution
~to a yellow solution
~3H2O2 + 2[Cr(OH)6]^3- –> 2CrO4^2- + 2OH-
+8H2O

~[Cr(OH)6]^3- is oxidised to CrO4^2-

Question 4

Describe and explain what happens when chromate (in alkaline conditions) has Zinc and HCl added to it? (3)

Answer 4

~goes from yellow solution
~to a green solution
~as CrO4^2- is reduced to [Cr(H2O)6]^3+