Write the equation for the manufacture of potassium dichromate from chromite ore.

Potassium dichromate K 2 Cr 2 O 7 acts as an oxidising agent and can be produced from chromite ore. Therefore, the following chemical reactions will take place- 4 FeCr 2 O 4 Chromite ore + 8 Na 2 CO 3 + 7 O 2 → 8 Na 2 Cr 2 O 4 Sodium chromite + 2 Fe 2 O 3 + 8 CO 2 2 Na 2 Cr 2 O 4 + H 2 SO 4 → Na 2 Cr 2 O 7 + Na 2 SO 4 + H 2 O Na 2 Cr 2 O 7 Sodium dichromate + 2 KCl → K 2 Cr 2 O 7 Potassium dichromate + 2 NaCl

Name one 3d series element that do not show variable oxidation state.

The element in 3d series that does not show variable oxidation state is scandium because of half filled d-orbitals in the ground state. Its atomic number is 21, therefore the number of electron in 3d and 4s orbitals is 1 and 2. So, it loses 1 electron from d orbital and 2 electrons from s orbitals. This results in the formation of stable inert gas configuration by removing three electrons from its d orbitals.

Transition elements show catalytic property. Give two reasons.

Transition metals and their compounds show good catalytic property. A good catalyst needs to adsorb the reactant molecules strongly enough for them to react, but not so strongly that the product molecules stick more or less permanently to the surface.Platinum, iron, vanadium pentoxide, nickel, etc., are catalysts. This is mainly due to- The presence of vacant d orbitals. They have the ability to exhibit variable oxidation states. They have a tendency to form complex compounds. Example- Iron in the Haber's Process, Nickel in the hydrogenation of C = C bonds, etc. Also, large surface area on which reactants are absorbed increases the concentration and weakens the bond in the reactant molecules. Consequently, lowering the activation energy.

Give two reasons. The chemistry of actinoids is more complicated than Lanthanoids.

The chemistry of actinoids is more complicated than lanthanoids because of the following reasons- Actinoids are radioactive in nature and have very fewer half-lives. 5f orbital of actinoids is more exposed to the outer environment. Whereas, in lanthanoids 4f orbital are deeply buried. Actinoids are also prepared in nanograms.

Give reason: Ti 4 + salts are colourless whereas Cr 3 + salts are coloured.

The colour of the first row (aquated) transition metal ion is due to an incompletely filled d-subshell. For the compound to be coloured it is essential to have unpaired electrons in d-subshell. As we know that the more the number of unpaired electrons present in the ion, the element will show colour due to the transition of the electrons from the ground state to the excited state. In the case of Ti 4 + salts, there are no unpaired electrons that mean the shells are fully filled. So, they will not show any colour. While in the case of Cr 3 + , there are 3 unpaired electrons present in d-shell. So, they will show violet colour in the solution.

Why 3d-series of elements acts as good catalyst?

3d-series of elements function as good catalysts either because of their ability to change oxidation state or in the case of the metals, to adsorb other substances onto their surface and activate them in the process. They can lend electrons or withdraw electrons from the reagent, depending on the nature of the reaction. The ability of transition metals to be in a variety of oxidation states, the ability to interchange between the oxidation states and the ability to form complexes with the reagents and be a good source for electrons make transition metals good catalysts.

Cerium ( Ce ) exhibits + 4 oxidation state. Give reason.

The electronic configuration of cerium Ce is Xe 4 f 1 5 d 1 6 s 2 . So to achieve the inert gas configuration it has to lose the outermost four electrons present in s, d and f orbitals. [ Xe ] 4 f 0 is the electronic configuration of nearest noble gas. It loses 4 electrons to complete its octets and attain stability to become Ce 4 + . Therefore, the oxidation state of cerium ( Ce ) is + 4 .

How is potassium permanganate KMnO 4 prepared from MnO 2 ? Write the equations.

Potassium permanganate KMnO 4 is prepared by the fusion of pyrolusite MnO 2 . In the first step when, pyrolusite ore is fused with an alkali metal hydroxide like Potassium hydroxide in the presence of air and potassium manganate (dark green) is formed. 2 MnO 2 + 4 KOH + O 2 → 2 K 2 MnO 4 Potassium manganate + 2 H 2 O In the second step, potassium manganate is treated with chlorine or carbon dioxide which disproportionate potassium manganate in a neutral or acidic solution to form potassium permanganate. K 2 MnO 4 + Cl 2 → 2 KCl + KMnO 4 Potassium permanganate

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - The d- and f-Block Elements>Karnataka Board-2018>Q 2

EASY

12th Karnataka Board

IMPORTANT

Earn 100

Give reason: Actinoid contraction is greater from element to element than lanthanoid contraction.

Chapter-Wise 3D Chemistry Videos from Embibe Experts EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY

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Oxidation States of Actinoids

The elements in the actinoid group are found to exhibit a large number of oxidation states. This property has contributed to making their chemistry more comp...

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Comparing the Lanthanoids and Actinoids

The Lanthanoids and actinoids are important groups of inner transition elements. Do you know the context in which they differ? Let’s explore some of their si...

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Lanthanoid Contraction

The steady decrease in atomic and ionic sizes of lanthanide elements with increasing atomic number is called lanthanoid contraction. It affects certain prope...

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