PUC Science 2nd PUC Class 12 - Karnataka Board PUC Important Questions for Chemistry

Define the following terms : Molarity

Define the following term: 

Molal elevation constant (K_b)

A solution of glucose (molar mass = 180 g mol^–1) in water is labelled as 10% (by mass). What would be the molality and molarity of the solution ? (Density of solution = 1.2 g mL^–1)

Define Molality.

From the given cells:

Lead storage cell, Mercury cell, Fuel cell and Dry cell

Answer the following:

(i) Which cell is used in hearing aids?

(ii) Which cell was used in Apollo Space Programme?

(iii) Which cell is used in automobiles and inverters?

(iv) Which cell does not have long life?

Following reactions occur at cathode during the electrolysis of aqueous silver chloride solution :

`Ag^+(aq)+e^(-)rarrAg(s)" ""      ""       "E^@=+0.80V`

`H^+(aq)+e^(-)rarr1/2H_2(g)" "" "" " E^@=0.00V`

On the basis of their standard reduction electrode potential (E°) values, which reaction is feasible at the cathode and why ?

Why conductivity of an electrolyte solution decreases with the decrease in concentration ?

Calculate Δ_rG^° for the reaction 

Mg (s) + Cu²⁺ (aq) → Mg²⁺ (aq) + Cu (s)

Given : E^°_cell = + 2.71 V, 1 F = 96500 C mol^–1

Define “zero order reaction”.

Write two factors that affect the rate of reaction.

For a reaction : 

(i) Write the order and molecularity of this reaction.

(ii) Write the unit of k.

The rate constant for the first-order decomposition of H₂O₂ is given by the following equation:

`logk=14.2-(1.0xx10^4)/TK`

Calculate E_a for this reaction and rate constant k if its half-life period be 200 minutes.

(Given: R = 8.314 JK^–1 mol^–1)

For the hydrolysis of methyl acetate in aqueous solution, the following results were obtained :

(i) Show that it follows pseudo first order reaction, as the concentration of water remains constant.

(ii) Calculate the average rate of reaction between the time interval 30 to 60 seconds.

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

A first order reaction takes 30 minutes for 50% completion. Calculate the time required for 90% completion of this reaction.

(log 2 = 0.3010)

The decomposition of NH₃ on platinum surface is zero order reaction. What are the rates of production of N₂ and H₂ if k = 2.5 × 10⁻⁴ mol⁻¹ L s⁻¹?

Account for the following: 

Cr²⁺ is a strong reducing agent.

When chromite ore FeCr₂O₄ is fused with NaOH in presence of air, a yellow-coloured compound (A) is obtained, which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with KCl forms an orange coloured crystalline compound (C).

(i) Write the formulae of the compounds (A), (B) and C.

(ii) Write one use of compound (C).

Complete the following chemical equation

8MnO₄^- + 3S₂O₃^2- + H₂O →

What are the transition elements? Write two characteristics of the transition elements.

How would you account for the following:

Actinoid contraction is greater than lanthanoid contraction.