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The Marsh test treats the sample with sulfuric acid and arsenic-free zinc. Even if there are minute amounts of arsenic present, the zinc reduces the trivalent arsenic (As 3+). Here are the two half-reactions: Oxidation: Zn → Zn 2+ + 2 e − Reduction: As 2 O 3 + 12 e − + 6 H + → 2 As 3− + 3 H 2 O. Overall, we have this reaction:
Arsenic forms colorless, odorless, crystalline oxides As 2 O 3 ("white arsenic") and As 2 O 5 which are hygroscopic and readily soluble in water to form acidic solutions. Arsenic(V) acid is a weak acid and the salts are called arsenates , [ 5 ] the most common arsenic contamination of groundwater , and a problem that affects many people.
James Marsh (2 September 1794 – 21 June 1846) was a British chemist who invented the Marsh test for detecting arsenic.Born in Kent, he was working as a labourer in Woolwich in the late 1810s and early 1820s, before joining the Royal Artillery. [1]
It is rapidly transformed into grey arsenic by light. The yellow form has a density of 1.97 g/cm 3. [23] Black arsenic is similar in structure to black phosphorus. [23] Black arsenic can also be formed by cooling vapor at around 100–220 °C and by crystallization of amorphous arsenic in the presence of mercury vapors. [26] It is glassy and ...
Trimethylarsine has been reported only at trace levels (parts per billion) in landfill gas from Germany, Canada, and the U.S.A., and is the major arsenic-containing compound in the gas. [5] [6] [7] Trimethylarsine is pyrophoric due to the exothermic nature of the following reaction, which initiates combustion: AsMe 3 + 1/2 O 2 → OAsMe 3 (TMAO)
Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolized to a less toxic form of arsenic through a process of methylation. [7] Organoarsenic compounds arise via biomethylation of inorganic arsenic compounds, [8] via processes mediated by enzymes related to vitamin B 12. [9]
When administered intravenously, a steady state is reached after 8–10 days. Arsenic binds to proteins to an insignificant extent. The highest concentrations of arsenic are found in the liver, kidneys, heart, lungs, hair, and nails. Arsenous acid is oxidized to arsenic acid and methylated in the liver, [65] [66] [67] and then excreted 60% in ...
The arsenic (As) cycle is the biogeochemical cycle of natural and anthropogenic exchanges of arsenic terms through the atmosphere, lithosphere, pedosphere, hydrosphere, and biosphere. Although arsenic is naturally abundant in the Earth's crust, long-term exposure and high concentrations of arsenic can be detrimental to human health. [1] [2]