How will you convert potassium chromate to potassium dichromate ? Mention the colour change involved in the reaction.

Potassium dichromate K 2 Cr 2 O 7 acts as an oxidising agent and can be produced by acidification of potassium chromate. Therefore, the following chemical reaction will take place- 2 K 2 CrO 4 potassium chromate Yellow + H 2 SO 4 → K 2 Cr 2 O 7 potassium dichromate Orange - red + K 2 SO 4 + H 2 O Due to the formation of potassium dichromate, the colour changes from yellow to orange-red during the reaction.

Why do transition elements form complexes ?

Transition elements have good tendency to form complexes. This is almost unique in their ability to form coordination compounds. This is due to the following reasons- They are very small. They have high positive charge density. They have vacant inner d-orbitals with suitable energy to accept lone pair of electrons. For eg- Cu NH 3 4 2 + , Ag NH 3 2 +

Write the uses of lanthanoid and actinoids.

The applications of lanthanoids and actinoids are the following: (i) Uranium is an actinide that is used in nuclear reactors. (ii) The lanthanoids elements are used inside the colour television tubes. (iii) Lanthanoids are used in hybrid cars, superconductors and permanent magnets. (iv) Thorium is an actinide that is used majorly in Gas mantles. (v) Lanthanoids are used in metallothermic reactions, and cerium salt is used in lead storage batteries as a catalyst. (vi) Plutonium is used in the treatment of cancer.

Write a note on Chrome plating.

When the surface of a metal is coated with a thin-layer of chromium, it is called chrome plating. Chromium metal is wear resistant and non-corrosive in nature. The layer should be less than 0 . 025 mm . This process can be used as decorative and for hardening other metal surfaces. Chromium plating is mainly observed on water taps, car parts, gas burners, etc.

[ Ti ( H 2 O ) 6 ] 3 + is coloured while [ Sc ( H 2 O ) 6 ] 3 + is colourless. Explain.

Transition metal ions show colour due to the presence of unpaired electrons in d - orbital. Due to the electronic transition, transition metal ions or compounds show colour. Outer electronic configuration of Sc 3 + = Ar 3 d 0 4 s 0 Outer electronic configuration of Ti 3 + = Ar 3 d 1 4 s 0 Oxidation state of Sc in Sc H 2 O 6 3 + is + 3 Oxidation state of Ti in the Ti H 2 O 6 3 + is + 3 . Since, Sc has no electrons in the d - orbital and no unpaired electron is present in the d subshell of metal ion hence d - d - transition is not possible. Therefore, it would be colourless. While Ti has 1 unpaired electron and due to this unpaired electron in the complex d - d transition is possible and hence it appears coloured. Therefore, Ti H 2 O 6 3 + ion is coloured.

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Transition and Inner Transition Elements>Tamilnadu Board-2018>Q 1

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Which of the following ions will give colourless aqueous solution?

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