Education Journalist | Study Abroad Lead
Cobalt II nitrate is a pale red powder-like inorganic chemical compound. It is a crystalline compound which is odourless and polar in nature. It is a nitrate salt whose composition is cobalt where it is in a +2 oxidation state and the anion is nitrate. It has a three dimensional polymeric network structure where each of the cobalt atoms is octahedrally coordinated by six oxygen atoms.
| Table of Content |
Key Terms: Compound, Cobalt, Nitrate, Ions, Atom, Oxygen, Hydrate, Oxidation State, Polar, Reaction, Anhydrous
Structure and Composition of Cobalt II Nitrate
[Click Here for Sample Questions]
There are several hydrate compounds of cobalt available. The general formula of Cobalt II Nitrate is Co(NO3)2 or CON2O6. The anhydrous form of cobalt II nitrate has a three-dimensional polymeric structure where each of the cobalt atoms is octahedrally coordinated by six oxygen atoms. Each nitrate ion is coordinated to three cobalt atoms. The dihydrate is a two-dimensional polymer having nitrate bridges between cobalt centres and all the two-dimensional layers are held by hydrogen bonds.
Structure of Cobalt II Nitrate
Formula of Cobalt II Nitrate
[Click Here for Sample Questions]
Cobalt II nitrate is an inorganic compound having a general formula Co(NO3)2.xH2O. In this compound, cobalt is in +2 state. The most common form of cobalt nitrate is Co(NO3)2.6H2O. The common form is the hexahydrate which is reddish-brown in colour, deliquescent and a polar compound. The molecular formula for cobalt nitrate is Co(NO3)2. The IUPAC name is Cobalt II Nitrate hexahydrate.
- Each of the nitrate ions is bonded to 3 cobalt ions. The dihydrate may be a two-dimensional polymer with nitrate bridges between cobalt centres and hydrogen bonding holding the 2D layers together. The tetrahydrate is made up of discrete and octahedral [(H2O)4Co(NO3)2] molecules.
- The hexahydrate is similar to hexaaquacobalt II nitrate [Co(H2O)6][NO3]2.
- The resemblance is due to discrete [Co(H2O)6]+2 and [NO3]2 2-.
Production of Cobalt II Nitrate
[Click Here for Sample Questions]
Cobalt nitrate(II) (hexahydrate) is prepared from treating metallic cobalt or one among its oxide. It also includes carbonates and hydroxides with aqua fortis. The subsequent reaction produces cobalt II nitrate.
Co + 4HNO3 + 4H2O → Co(H2O)6(NO3)2 + 2NO2
CoO + 2HNO3 + 5H2O → Co(H2O)6(NO3)2
CoCO3 + 2 NO3 + 5H2O → Co(H2O)6(NO3)2 + CO2
Another method for producing cobalt II nitrate is putting metal cobalt into a pressure resistant and anti nitric acid corrosive container. And allowing industrial pure oxygen to perform dissolving reactions of metal cobalt with a temperature between 20o C to 100 oC. The required pressure for the reaction is 0.05mPa and 0.5mPa and the aqua fortis concentration should be between 1mol/L to 14mol/L. The quantity of cobalt for the reaction is larger than the quantity calculated by chemical equation. The reaction therefore, can last for 1 to 10 hours. Three different of dissolution reactions occurs with metallic cobalt
Co + 4HNO3 → Co(NO3)2 + 2NO2 + 2H2O
3Co + 8 hops → 3Co(NO3)2 + 2NO + 4H2O
3NO2 + H2O → 2 + NO hop
The overall reaction is:
2Co + 4HNO3 + O2 → 2Co(NO3)2 + 2H2O
Uses of Cobalt II Nitrate
[Click Here for Sample Questions]
Mentioned below are a few uses of cobalt nitrate:
- Cobalt nitrate is used in making porcelain and stones.
- It is used in the production of invisible inks and cobalt pigments.
- It is used in making hair dyes and animal feeds.
- It is used as an additive to soils and also as a vitamin supplement.
- It is used in catalyst preparation.
Things to Remember
[Click Here for Sample Questions]
- Cobalt II Nitrate is an inorganic compound having a general formula Co(NO3)2.xH2O
- This compound is odourless and is polar in nature.
- Each of the nitrate ions is bonded to 3 cobalt ions in cobalt nitrate.
- Hexahydrate is mostly reduced to extract cobalt of high purity.
- Cobalt nitrate is used in the production of invisible inks and cobalt pigments.
- The molecular weight of anhydrous Cobalt II Nitrate is 182.941g/mol (291.03 g/mol hexahydrate) and it’s density is 2.49 g/cm3 (1.87 g/cm3 hexahydrate).
- The melting and boiling points of anhydrous Cobalt II Nitrate are 100oC (55o C hexahydrate) and 100-105o C (74oC hexahydrate).
Sample Questions
Ques. A green mass is formed when zinc oxide is heated with cobalt nitrate. Name the compound? (2 marks)
Ans. When zinc oxide is heated with cobalt nitrate, a green mass is formed due to the formation of a compound. This compound is Co(ZnO2). It is also called rinmann’s green. It is a translucent pigment green in colour.
Ques. How does ligand exchange of hexaaquacobalt II ions with hydroxide ions occur? (2 marks)
Ans. Hydroxide ions remove hydrogen ions from the water ligands attached to the cobalt ion. Once a proton has been far away from two water molecules, we’re left with a complex with no charge which is a neutral complex. This is insoluble in water and thus it leads to formation of a precipitate.
Co(H2O)62+ + 2OH– → [Co(H2O)4(OH)2] + 2H2O(aq)
Ques. How does the exchange of ligands in hexaaquacobalt(II) ions with ammonia solution take place? (3 marks)
Ans. The ammonia acts as base and also a ligand. With a little amount of ammonia, hydrogen ions are formed. The hexaaqua ion is exactly within the hydroxyl ion case to offer an equivalent neutral complex.
[Co(H2O)6]2+ + 2NH3 → [Co(H2O)4(OH)2] + 2NH4
That precipitate dissolves if you add more than ammonia. The added ammonia replaces water( because ammonia is a strong ligand) to provide hexaamminecobalt(II) ions.
[Co(H2O)6]2+ + 6NH3 → [Co(NH3)6]2+ + 6H2O
Ques. What happens in the cobalt nitrate test? What colour does it give with Zn and Mg? (3 marks)
Ans. In a cobalt nitrate test, a drop of cobalt nitrate solution is added over the residue in the charcoal cavity. Just after it, it is heated in an oxidising flame. Cobalt nitrate decomposes to form cobalt oxide- CoO. The cobalt oxide reacts with metallic oxides present in charcoal activity as a white residue and forms colored compounds having different colours.
So, cobalt nitrate test for Zn and Mg-
MgO + CoO → MgO.CoO (pink)
ZnO + CoO → ZnO.CoO (green)
It is observed that Zn gives green colour with cobalt nitrate and Mg gives pink colour.
Ques. What happens when a philosopher's wool is treated with cobalt nitrate? (3 marks)
Ans. Now when we mix philosopher’s wool with cobalt nitrate, the reaction takes place in 2 steps, firstly Cobalt nitrate breaks and the product reacts with zinc oxide.
2Co(NO3)2− → 2CoO + 4NO2 + O2
Then cobalt oxide reacts with philosopher’s wool ZnO, zinc oxide.
CoO + ZnO → ΔCoZnO2
This product is Rinnman’s Green.
Ques. If hydrochloric acid is mixed with cobalt nitrate solution at room temperature, then this reaction takes place:
[Co(H2O)6]3+ + 4Cl-(aq) [Cocl4]2- + 6H2O(l)
What is the colour of the reaction mixture? What happens when it cools?What is the sign of H for this reaction? (3 marks)
Ans. The colour of the reaction mixture becomes blue on reacting. When cooled, the colour becomes pink. The H for this reaction is positive.
[Co(H2O)6]3+ + 4Cl-(aq) [Cocl4]2- + 6H2O(l)
When cooled the reaction moves to backward direction, this means that the backward reaction is exothermic. Therefore we can conclude that the forward reaction is an endothermic reaction. This means H will be positive.
Ques. Why do transition metals have variable oxidation states? How is it different from p block elements? (2 marks) [2017 delhi]
Ans. The variability in oxidation states of transition metal is due to the incomplete filling of D orbitals in such a way that their oxidation states differ from each other by unity, Fe2+ and Fe3+, etc. In the case of p block elements, the oxidation states differ by units by two e.g. +3 and +5. In transition elements, the higher oxidation states are found to be more stable for heavier elements in the group, E.g. Mo+6 is found to be more stable than Cr+4. In p- block elements the lower oxidation states are more stable for heavier members due to the inner pair effect, e.g, Pb+2 is found to be more stable than Pb+4.
Ques. A green mass is formed in the charcoal cavity test when a colourless salt A is fused with cobalt nitrate. What is the metal in A ? Write all the reactions. (3 marks)
Ans. The metal A in the salt is zinc. The salt is Zinc sulphate. These are the following reactions of cobalt nitrate tests.
ZnSO4 + Na2CO3 = ZnCO3 + Na2SO4
ZnCO3 = ZnO + CO2
2Co(NO3)2 = 2CoO + 4NO2 + O2
CoO + ZnO = CoZnO2 [green]
Ques. Write some of the applications of cobalt? (2 marks)
Ans. Cobalt is extensively used in the production of super alloys. Super alloys consist of iron, cobalt, nickel, tungsten, titanium, aluminium.Super alloys are rust free,they don’t get rusted easily and retain their physical and chemical properties at high temperatures. Cobalt also helps in producing magnetic alloys which are used in devices that require magnetic fields. For example, cobalt is used in electric motors and generators. Cobalt is also used in production of cemented carbides.
Ques. What are the various effects of cobalt on the human body? (2 marks)
Ans. Cobalt is a micronutrient which is required by the body in small amounts. When micronutrients are absent in the body, it leads to health problems. Animals use these minerals to produce essential enzymes which act as catalysts. These catalysts are responsible for speeding up many processes inside the body. Enzymes are needed for the body to function properly. Cobalt is needed for our body to produce vitamin B-12. Vitamin B-12 ensures that red blood cells are produced in the required amount in the body.
Ques. How can we convert cobalt nitrate to cobalt chloride? (5 marks)
Ans. It is known that Co(NO3) can react with conc HCL to produce CoCl2 but there is a slight chance of it forming a complex [CoCl3]4-. Therefore it is indirectly prepared.
First cobalt nitrate is heated strongly to give CoO.
2Co(NO3)2 = 2CoO + 4NO2 + O2
Both NO2 and O2 are gases except CoO. Some of CoO may also get oxidised to Co2O3.
4CoO + O2 = 2Co2Co3
And we get a mixture of
CoO + Co2O3 = Co3O4
But both will react with Cl2 to give CoCl2.
2CoO + Cl2 = CoCl2 + O2
Co3O4 + Cl2 = CoCl2 + 2O2
Read More:
Comments