Science (English Medium) Class 12 - CBSE Important Questions for Chemistry

Give reasons for the following :

Aquatic animals are more comfortable in the cold water than in warm water.

Give reasons for the following

Elevation of the boiling point of 1 M KCl solution is nearly double than that of 1 M sugar solution.

An element 'X' (At. mass = 40 g mol^-1) having f.c.c. the structure has unit cell edge length of 400 pm. Calculate the density of 'X' and the number of unit cells in 4 g of 'X'. (N_A = 6.022 × 10²³ mol^-1)

For the reaction

`2AgCl (s) + H_2 (g) ("1 atm") -> 2Ag (s) + 2H^(+)  (0.1 M) +  2Cl^(-) (0.1 M)`

`triangleG^0 = -43600 J at 25^@ C`

Calculate the e.m.f. of the cell

`[log 10^(-n) = -n]` 

Write two advantages of fuel cell

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.

Write the formula for the given coordination compound:

Iron (III) hexacyanoferrate (II)

CO (g) and H₂ (g) react to give different products in the presence of different catalysts. Which ability of the catalyst is shown by these reactions?

Write the coordination number and oxidation state of Platinum in the complex [Pt(en)₂Cl₂].

What happens when a freshly prepared precipitate of Fe(OH)₃ is shaken with a small amount of FeCl₃ solution?

What happens when persistent dialysis of a colloidal solution is carried out?

What happens when an emulsion is centrifuged?

(A), (B) and (C) are three non-cyclic functional isomers of a carbonyl compound with molecular formula C₄H₈O. Isomers (A) and (C) give positive Tollens' test whereas isomer (B) does not give Tollens' test but gives positive Iodoform test. Isomers (A) and (B) on reduction with Zn(Hg)/conc. HCl give the same product (D).

1) Write the structures of (A), (B), (C) and (D).

2) Out of (A), (B), and (C) isomers, which one is least reactive towards the addition of HCN?

Write the structures of the main products in the following reactions :

What type of isomerism is exhibited by the complex [Co(NH₃)₅Cl]SO₄?