Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions

Following are the transition metal ions of 3d series:

Ti⁴⁺, V²⁺, Mn³⁺, Cr³⁺

(Atomic numbers: Ti = 22, V = 23, Mn = 25, Cr = 24)

Answer the following:

1) Which ion is most stable in an aqueous solution and why?

2) Which ion is a strong oxidising agent and why?

3) Which ion is colourless and why?

How would you account for the following? 

Zr (Z = 40) and Hf (Z = 72) have almost identical radii.

How would you account for the following? 

Transition metals and their compounds act as catalysts.

An analysis shows that FeO has a non-stoichiometric composition with formula Fe_0.95O. Give reason.

Complete and balance the following chemical equations

`Fe^(2+) + MnO_4^(-) + H^+ ->`

Complete and balance the following chemical equations

`MnO_4^(-) + H_2O + I^(-) ->`

Give reasons: 

E° value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Fe³⁺/Fe²⁺.

Give reasons Iron has the higher enthalpy of atomization than that of copper.

Give reasons: Sc³⁺ is colourless in aqueous solution whereas Ti³⁺ is coloured.

Shyam went to a grocery shop to purchase some food items. The shopkeeper packed all the items in polythene bags and gave them to Shyam. But Shyam refused to accept the polythene bags and asked the shopkeeper to pack the items in paper bags. He informed the shopkeeper about the heavy penalty imposed by the government for using polythene bags. The shopkeeper promised that he would use paper bags in future in place of polythene bags.

1) Write the values (at least two) shown by Shyam.

2) Write one structural difference between low-density polyethene and high-density polyethene.

3) Why did Shyam refuse to accept the items in polythene bags?

4) What is a biodegradable polymer? Give an example.

Write the cell reaction and calculate the e.m.f of the following cell at 298 K:

Sn_(s) | Sn²⁺ (0.004 M) || H⁺ (0.020 M) | H_2(g) (1 bar) | Pt_(s)

(Given: `E_(Sn^(2+)"/"Sn)^° = -0.14` V)

Write the IUPAC name of the given compound :

Physisorption is reversible while chemisorption is irreversible. Why ?

Why do transition elements show variable oxidation states ? In 3d series (Sc to Zn), which elements shows the maximum number of oxidation state and why ?

Give reasons for the following observations :

 Powdered substances are more effective  adsorbents.

Account for the following :

Bond angle in NH+4NH4+ is higher than NH₃.

Give simple chemical tests to distinguish between the following pair of compounds:

Benzaldehyde and Benzoic acid

Which component of starch is a branched polymer of α-glucose and insoluble in water?

Using IUPAC norms, write the formula of Hexaamminecobalt(III) sulphate.

 Tendency to show –3 oxidation state decrease from Nitrogn (N) to Bismuth (Bi).