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Chapter_14 Notes

Chapter_14 Notes - Group 15 N P As Sb Bi Shriver Chapter 14...

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1 Group 15 Shriver, Chapter 14 N, P, As, Sb, Bi known as pnictogens As, Sb metalloids, Bi metal Increasing metallic character down the group, but metallicity is not pronounced Major oxidation states: V, III, I; but V not stable for N; increasing stability of oxidation state I down the group Origins and Preparation Nitrogen - element first isolated in 1772 by burning an organic compound in a limited amount of air, then taking up the CO 2 in a KOH solution - ancient names: o Chaptal: Greek nitron , constituent of nitrate (known to the ancients) o in Libya: chunks of NH 4 Cl found in hills called sal ammoniac – salt belonging to Ammon (Egyptian god Amun) o Lavoisier: Greek azote , lifeless (French: azote ) o German: Stickstoff (sticken, to choke or suffocate) - triple bond in gas phase, highly unreactive due to high bond strength and low polarizability - 78% of air by volume (note: S&A incorrectly state wt%) - separated from air by fractional distillation or pressure swing adsorption using zeolites - not abundant in Earth’s crust: only 19 ppm (similar to Ga, Nb, Li) - found as NaNO 3 and KNO 3 (salt petre), highly sought for explosives before Haber process - a component of amino acids (15 wt% of proteins), nucleic acids - source of fertilizer: N 2 fixation by legumes (natural) or industrial: Haber process (NH 3 ) and Ostwald process (HNO 3 ), now larger scale than natural - high nitrate concentrations in drinking water can be toxic - used to create inert atmosphere (glovebox, Schlenk line) for work with air- sensitive compounds, on a large scale for metals processing - used as a cryogen (liq N 2 bp 77 K) Phosphorus (note us spelling) - no volatile naturally occurring compounds - element has several solid allotropes: o white phosphorus (P 4 molecules), pyrophoric (slightly volatile, vapor oxidizes with chemiluminescence), mp 44 °C, insoluble in water, highly toxic (even skin contact), fatal dose 50 mg, dissociation to P 2 only at high T watch the video: combustion of white phosphorus under water
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2 http://www.cci.ethz.ch/experiments/P_unter_H2O/en/stat.html watch the video: Self-ignition of white phosphorus http://www.cci.ethz.ch/experiments/P-O2/en/stat.html watch the video: Combustion of white phosphorus in air http://www.cci.ethz.ch/experiments/P4-Luft/en/stat.html o red phosphorus, 3D solid, not pyrophoric (red strip for striking matches) made by heating P 4 in inert atmosphere, mp 600 °C, non-toxic o black phosphorus, denser 3D solid, made by heating P 4 in an inert atmosphere at high pressure - element first isolated (as P 4 ) in 1669, by distillation of putrified urine - name from the Greek phos (light) and phoros (bringing) - 1120 ppm in crustal rocks, highly insoluble Ca 3 (PO 4 ) 2 (K sp 10 -29 , even lower for apatites) - crude phosphoric acid obtained from phosphate rock (e.g., hydroxyapatite) o Ca 4 (PO 4 ) 3 OH + 5 H 2 SO 4 3 H 3 PO 4 + 5 CaSO 4 + H 2 O - pure phosphoric acid made by carbon reduction with silica o Ca 4 (PO 4 ) 3 OH + SiO 2 6 CaSiO 3 + P 4 O 10 o P 4 O 10 + 10 C P 4 + 10 CO o P 4 purified by sublimation, oxidized to P 4 O 10 and hydrated to H 3 PO 4 -
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