Science (English Medium) Class 12 - CBSE Question Bank Solutions for Chemistry

Give reasons  Although –NH₂ is o/p directing group, yet aniline on nitration gives a significant amount of m-nitroaniline

Do the following conversions in not more than two steps :

Ethyl benzene to Benzoic acid

Do the following conversions in not more than two steps :

Propanone to Propene

Following data are obtained for reaction :

N₂O₅ → 2NO₂ + 1/2O₂

1) Show that it follows first order reaction.

2) Calculate the half-life.

(Given log 2 = 0.3010, log 4 = 0.6021)

A 10% solution (by mass) of sucrose in water has freezing point of 269.15 K. Calculate the freezing point of 10% glucose in water, if freezing point of pure water is 273.15 K

Given : (Molar mass of sucrose = 342 g mol⁻¹)

(Molar mass of glucose = 180 g mol⁻¹)

Account for the following:

E° value for the Mn³⁺/Mn²⁺ couple is highly positive (+1.57 V) as compare to Cr³⁺/Cr²⁺.

Write the structure of 2,4-dinitrochlorobenzene

Write the formula of an oxo-anion of Chromium (Cr) in which it shows the oxidation state equal to its group number

A first order reaction takes 20 minutes for 25% decomposition. Calculate the time when 75% of the reaction will be completed.

(Given : log = 2 = 0·3010, log 3 = 0·4771, log 4 = 0·6021)

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)