A chemist wishes to prepare a buffer solution of pH = 2.90 that e

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411.

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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412.

NaOH is a strong base. What will the be pH of 5.0 × 10-2 M NaOH solution? (log 2 = 0.3)

  • 14.00

  • 13.70

  • 13.00

  • 12.70


413.

The equilibrium constants of the reactions

SO2(g) + 12O2(g)  SO3(g) and 2SO2(g) + O2(g)  2SO3(g) are K1 respectively. The relationship between K1 and K2 will be

  • K12=K2

  • K2 = √K1

  • K1= K2

  • K23 = K1


414.

The value of Kc for the dissociation reaction, H2 (g)  2H (g) is 1.2 × 10-42

This equilibrium mixture contains mainly

  • H2 (g)

  • H (g) atom

  • 1.1 M mixture of H2 and H

  • 1.2 M mixture of H2 and H


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415.

Among the following, the equilibrium which is not affected by an increase in pressure is

  • C(s) + H2O (g)  CO(g) + H2(g)

  • 3Fe(s) + 4H2O (g) Fe3O4 (s) + 4H2(g)

  • 2SO3(g) 2SO2(g) + O2 (g)

  • H2 (g) + I2(s) 2Hi(g) 


416.

Ksp of CaSO4 is 4 × 10-12. CaSO4 is precipitated on mixing equal volumes of the following solutions.

  • 3 × 10-10 M CaCl2 and 3 × 10-6 M (NH4)2SO4

  • 4 × 10-6 M CaCl2 and 3 × 10-6 M (NH4)2SO4

  • 6 × 10-6 M CaCl2 and 3 × 10-16 M (NH4)2SO4

  • In all the above cases


417.

What is pH of 2 x 10-8 molar HCl solution? Here, log 2 = 0.301 and log 3 = 0.477.

  • 6.92

  • 9.5

  • 5.4

  • 7.7


418.

Which one of the following species acts as both Bronsted acid and base?

  • H2PO2-

  • HPO32-

  • HPO42-

  • All of these


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419.

The reaction, SO2 + O2 → 2SO2 + Heat.

The equilibrium reaction proceeds in forward direction by

  • addition of O2

  • removal of O2

  • addition of inert gas

  • cannot proceed


420.

Which is soluble in NaNO3 and dil. HCl mixture and forming salt?

  • (CH3)3CNH2

  • (CH3)2CHNH2

  • (CH3)2NH

  • (CH3)3N


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