Transition Metals

Question 1

colour of chromium

Answer 1

bluish white metal

Question 2

write interconvertble reaction between chromate and dichromate

Answer 2

CrO4 2- + H+ —> Cr2O7 2- + H2O

yellow chromate orange dichromate

Question 3

toxic side effects of chromate VI

Answer 3

• cancer in oral cavity/ small intestine
• kidney failure
• ulcers in the stomach
• damage to blood cells by causing haemolysis
• toxicity in the liver

Question 4

physical property of manganese

Answer 4

hard silver white metal

Question 5

reaction of heating of KMnO4

Answer 5

2KMnO4 –> K2MnO4 +MnO2 +O2

Question 6

potassium manganage VII reduction in alkaline solution

Answer 6

MnO4- + 2H2O + 3e- —-> MnO2 + 4OH-

forms manganese IV oxide, a black precipitate/brown pp

Question 7

potassium manganate VII reduction in acidic solution

Answer 7

MnO4- +8H+ +5e- —-> Mn2+ +4H2O

purple soln to a colourless solution of manganese II

Question 8

can KMnO4 be used to analyse solutions containing Cl- ions, or acidified using HCl?

Answer 8

no because it is a stronger oxisidisng agent than potasium dichromate and will oxidise Cl- to Cl2

Question 9

when is alkaline potassium manganate VII utilised?

Answer 9

to oxidize alkenes to diols

Question 10

explain the non existence of Iron III Iodide

Answer 10

down group 7, the oxidising power decreases allowing for I- to be a great reducing agent that wants to be oxidized to I2, whilst reducing Fe3+ to Fe2+

Question 11

explain the non existence of Fe III carbonate

Answer 11

in aq environemnets, iron III is bound to ligands as [Fe(H2O)6]3+. due to strong interactions the omplex can hydrolyse to liberate H+. carbonate is abase and captures H+. thisfurther facilitates the formation of hydroxyl complexes so much that it will produce H2CO3 and Fe(OH)3. H2CO3 will decompose into water and CO2.

as a solid it is hygroscopic and therefore absorb water. the above iwll then take place.

Question 12

in what 3 forms does iron occur?

Answer 12

-haematite- Fe2O3
magnetite Fe3O4
carbonate FeCO3

Question 13

acidity of IronIII and Iron II

Answer 13

iron IIIcomplex is hydrolysed to libertae 3 protons while iron II can liberate 2. Iron III is more acidic.

Question 14

test for Iron III ions

Answer 14

addition of potasium thiocyanate . colour change from yellow to deep red .
[Fe(H2O)6]3+ + SCN- —> [Fe(H2O)5SCN]2+ +H2O

Question 15

formation of Cu2O as seen in fehlings test

Answer 15

Cu2O (reddish brown) is made by the reduction of alkaline CuII solution. reducing agents like aldehydes and reducing sugars will reduce Cu2+ (blue) ion to Cu2O.
2Cu2+ +2OH- +2e- —> Cu2O +H2O
test for reducing sugars and aldehydes.

Question 16

explain instability of Cu+

Answer 16

it is unstable in solution with respect to disproportionation, to give Cu solid and Cu2+ ions.

2Cu+ (colourless) —> Cu2+ (blue) + Cu (s)

it is stable in solids

Question 17

how can Cu+ ions be stabilised?

Answer 17

water ligands as well as; [CuCl2]-

[Cu(CN)4]3- , [Cu(NH3)2]+ .

Question 18

reaction of Cu2O (Cu+) with acids (for CuCl)

Answer 18

forms copper I salts which disproportionate unless insoluble
Cu2O(s) +HCl —> CuCl(s) + H2O

Cu2O(s) + H2SO4 —> Cu2SO4 (aq) + H2O—> Cu(s) + CuSO4 +H2O

Question 19

formation of CuI , mention colour and solubility

Answer 19

white solid, insoluble in water.
from Cu2O:
Cu2O + I2 —-> CuI +O2
or Cu2O + HI —> CuI +H2O

from Cu2+ : Cu2+ + I- —. CuI + I2

Question 20

dichromate to chromate

Answer 20

Cr2O7 2- +14H+ +6e- 2Cr3+ +7H2O

from orange to green