Chemistry 12 Chapter 8 Exemplar Solutions the P and F Block Elements Part 5

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Question 44:

Explain why does colour of disappear when oxalic acid is added to its solution in acidic medium.

Answer:

acts as oxidising agent. It oxidises oxalic acid to and itself changes to which is colourless.

Question 45:

When orange solution containing is treated with an alkali, a yellow solution is formed and when ions are added to yellow solution, an orange solution is obtained. Explain why does this happen?

Answer:

Question 46:

A solution of on reduction yields either a colourless solution or a brown precipitate or a green solution depending on pH of the solution. What different stages of the reduction do these represent and how are they carried out?

Answer:

Oxidising behaviour of depends on of the solution. In acidic medium

Question 47:

The second and third rows of transition elements resemble each other much more than they resemble the first row. Explain why?

Answer:

Due to lanthanoid contraction, the atomic radii of the second and third row transition elements is almost same. So they resemble each other much more as compared to first row elements.

Question 48:

of is while that of is . Explain

Answer:

Hint: High ionisation enthalpy to transform is not balanced by its hydration enthalpy. However, in case of after removal of electrons from , stable configuration is acq

Question 49:

The halides of transition elements become more covalent with increasing oxidation state of the metal. Why?

Answer:

As the oxidation state increases, size of the ion of transition element decreases. As per Fajan’s rule, as the size of metal ion decreases, covalent character of the bond formed increases.

Question 50:

While filling up of electrons in the atomic orbitals, the orbital is filled before the orbital but reverse happens during the ionisation of the atom. Explain why?

Answer:

So electron will enter in 4s orbital.

Ionisation enthalpy is responsible for the ionisation of atom. electrons are loosely held by the nucleus. So electrons are removed from orbital prior

Question 51:

Reactivity of transition elements decreases almost regularly from to . Explain.

Answer:

Hint: It is due to regular increase in ionisation enthalpy.