The pKa of a weak acid (HA) is 4.5. The pOH of an aqueous buffered solution of H_A in which 50% of the acid is ionized is

• 4.5

• 2.5 

• 9.5

• 9.5

Assuming that water vapour is an ideal gas, the internal energy change(∆U) when 1 mol of water is vapourised at 1 bar pressure and 100°C, (Given: Molar enthalpy of vapourisation of water at 1 bar and 373 K = 41 kJ mol^-1 and R = 8.3 J mol^–1K^–1 will be) –

• 4.100 kJ mol^–1

• 3.7904 kJ mol^–1

• 37.904 kJ mol^–1

• 37.904 kJ mol^–1

Which of the following sets of quantum numbers represents the highest energy of an atom?

• n = 3, l = 1, m = 1, s = +½

• n = 3, l = 2, m = 1, s = +½

• n = 4, l = 0, m = 0, s = +½

• n = 4, l = 0, m = 0, s = +½

Which of the following hydrogen bonds is the strongest?

• O – H …… N

• F – H …… F

• O – H ….. O

• O – H ….. O

In the reaction,
2Al(s) + 6HCl(aq) → 2Al³⁺ (aq) + 6Cl¯(aq) + 3H₂(g)

• 6L HCl(aq) is consumed for every 3L H₂(g) produced

• 33.6 L H₂(g) is produced regardless of temperature and pressure for every mole Al that reacts

• 67.2 L H₂(g) at STP is produced for every mole Al that reacts

• 67.2 L H₂(g) at STP is produced for every mole Al that reacts

Regular use of which of the following fertilizers increases the acidity of soil ?

• Potassium nitrate

• Urea

• Superphosphate of lime

• Superphosphate of lime

Identify the correct statement regarding a spontaneous process –

• For a spontaneous process in an isolated system, the change in entropy is positive

• Endothermic processes are never spontaneous

• Exothermic processes are always spontaneous

• Exothermic processes are always spontaneous

The charge/size ratio of a cation determines its polarizing power. Which one of the following sequences represents the increasing order of the polarizing power of the cationic species, K⁺, Ca²⁺, Mg²⁺, Be²⁺?

• Mg²⁺ < Be²⁺ < K⁺ < Ca²⁺

• Be²⁺ < K⁺ < Ca²⁺ < Mg²⁺

• K⁺ < Ca²⁺ < Mg²⁺ < Be²⁺

• K⁺ < Ca²⁺ < Mg²⁺ < Be²⁺

In the conversion of limestone to lime, CaCO₃(s) → CaO(s) + CO₂(g) the values of ∆Hº and ∆Sº are + 179.1 kJ mol^–1 and 160.2 J/K respectively at 298K and 1 bar. Assuming that ∆Hº and ∆Sº do not change with temperature, temperature above which conversion of limestone to lime will be spontaneous is

• 1008 K

• 1200 K

• 845 K

• 845 K

The energies of activation for forward and reverse reactions for A₂ + B₂ ⇌ 2AB are 180 kJ mol^–1 and 200 kJ mol^–1 respectively. The presence of a catalyst lowers the activation energy of both (forward and reverse) reactions by 100 kJ mol^–1. The enthalpy change of the reaction (A₂ + B₂ → 2AB) in the
presence of catalyst will be (in kJ mol^–1) –

• 300

• 120

• 280

• 280