Subject

Chemistry

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

11.

The correct order of ionization energies is

  • Cu > Ag > Au

  • Cu > Au > Ag

  • Au > Cu > Ag

  • Ag > Au > Cu


12.

Among the following compounds both coloured and paramagnetic one is

  • K2Cr2O7

  • VOSO4

  • (NH4)2.[TiCl2]

  • K3[Cu(CN)4]


13.

Which of the following has maximum bond energy?

  • C=C

  • C=O

  • O=O

  • N=O


14.

An organic compound crystallises in an ortho rhombic system with two molecules per unit cell. The unit cell dimensions are 12.05, 15.05 and 2.69 Å. If the density of the crystal is 1.419 g cm-3, then molar mass of compound will be 

  • 207 g mol-1

  • 209 g mol-1

  • 308 g mol-1

  • 317 g mol-1


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15.

The molarity of a solution in which 5.3 g Na2CO3 is dissolved in 500 mL will be

  • 1.0 M

  • 0.1 M

  • 0.20 M

  • 0.2 M


16.

1 mL of 0.01 N HCl is added to 999 mL solution of 0.1 N Na2SO4. The pH of the resulting solution will

  • 2

  • 7

  • 5

  • 1


17.

The equilibrium constants for the reaction,

Br2  2Br → 1

at 500 K and 700 K are 1 × 10-10 and 1 × 10-5 respectively. The reaction is

  • endothermic

  • exothermic

  • fast

  • slow


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18.

A chemist wishes to prepare a buffer solution of pH = 2.90 that efficiently resists a change in pH yet contains only small concentration of buffering agents which one of the following weak acid along with its salt would be best to use 

  • m-chlorobenzoic acid (pKa = 3.98)

  • Acetoacetic acid (pKa = 3.58)

  • 2 5-dihydrobenzoic acid (pKa = 2.97)

  • p-chlorocmanic acid (pKa = 4.41)


C.

2 5-dihydrobenzoic acid (pKa = 2.97)

The buffer solution to be made should effectively resists a change in pH, i.e., should have a higher buffer capacity.

Buffer capacity (Φ) = No. of moles of acid or base added to 1LChange in pH

By one of any two ways, we can obtain it,

(i) The higher the concentration of the components of a buffer mixture, the greater will be the buffer capacity But, the condition is to maintain a small concentrations of buffering components.

(ii) Buffer capacity of a buffer is maximum when the concentration of the weak acid and its salt are equal, i.e. [salt] = [acid].

 pH = pKa + log [salt][acid]

         = pKa + log 1 (as [Salt] = [acid])

    pH = pKa = 2.9

As, 2, 5-dihydrobenzoic acid has pKa value = 2.97, hence, it is the best choice for chemist to prepare buffer solution.


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19.

If 5 L of H2O2 produces 50 L of O2 at NTP, H2O2 is

  • 50 volume

  • 10 volume

  • 5 volume

  • None of the above


20.

The wave number of hydrogen atom in Lyman series is 82200 cm-1. The electron goes from

  • n3 → n2

  • n2 → n1

  • n4 → n3

  • None of these


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