Chemistry Test 204

Scuba divers must cope with high concentrations of dissolved gases while breathing air at high pressure underwater. Increased pressure increases the solubility of atmospheric gases in blood. When the divers come towards surface, the pressure gradually decreases. This releases the dissolved gases and leads to the formation of bubbles of nitrogen in the blood. This blocks capillaries and creates a medical condition known as bends, which are painful and dangerous to life. To avoid bends, as well as, the toxic effects of high concentrations of nitrogen in the blood, the tanks used by scuba divers are filled with air diluted with helium (11.7% helium, 56.2% nitrogen and 32.1% oxygen).

The correct answer is B: Inert pair effect.

• As we move down the 15th group from nitrogen to bismuth, the s-electrons in the outermost shell increasingly resist participation in bonding.
• This phenomenon is known as the inert pair effect.
• The inert pair effect makes the +3 oxidation state more stable than the +5 oxidation state in heavier elements like bismuth.
• Thus, pentavalency becomes less pronounced and trivalency becomes more pronounced.

Liquid ammonia has high vapour pressure which is lowered down by cooling, otherwise the liquid will bump.

Ca₃P₂ + 6H₂O → 3Ca(OH)₂ + 2PH₃; i.e. 2 moles of phosphine are produced from one mole of calcium phosphide.

Molality is the moles of solute dissolved per kg of solvent therefore 500g,1 molal solution contains 0.5 of solute, as

∆T_f = K_f^m = 5.12 × 0.078 = 0.399K = 0.40K

Maximum boiling azeotropes are formed by those solutions which show negative deviations from Raoult's law. H₂O and HNO₃ mixture shows negative deviations

p_{water vapour} = x_{water vapour} × p_total = 0.02 × 1.2 = 0.024atm

p_total = p_water vapour × p_{Dry air}

⇒1.2 = 0.024 + p_{Dry air}

⇒ p_{Dry air} = 1.176atm

Partial vapour pressure is directly proportional to mole fraction, p ∝ x.