Azerbaijan is famous for mud volcanoes. About 400 active mud volcanoes are present in this region, b — Physical Chemistry — Kinetics Chemistry Question
An element typical for Azerbaijan mud volcanoes expelled water
Azerbaijan is famous for mud volcanoes. About 400 active mud volcanoes are present in this region, both onshore and offshore - more than half the total throughout the world. Mud volcanoes come in a variety of shapes and sizes, but those most common in Azerbaijan have several small cones, or vents, up to about four meters in height. Mud volcanic eruptions in Azerbaijan normally last for less than a few hours, and are characterized by vigorous extrusion of mud breccias, hydrocarbon gases, and waters. Bakhar is a mud volcano with a high seep activity in the dormant period. The reservoirs formed by the volcanoes’ activity contain the expelled waters. Those of Bakhar volcano have a composition with Na and Cl as dominant ions. The analyzed waters are enriched in metals and in an element X that causes flame coloration. Its’ concentration in seeping water of 250 ppm represents a 55-fold enrichment in comparison to seawater. Being concentrated, the expelled water gives the white crystals, among them the compound Y, one of the main sources of X. The common oxide of X contains 31.0 % of the element, whereas the compound Y – 11.3 % only.
What are the element X and the compound Y?
Model Answer
The general formula of an oxide is XOn. The molar ratio of X to O is: 31.0 / M(X) : 69.0 / 16 = 1 : n
n = 0.5; 1; 1.5; 2 etc.
n = 0.5 gives M(X) = 3.6 ⇒ no element.
n = 1 gives M(X) = 7.2 ⇒ Li, but it doesn’t exist in oxidation state II.
n = 1.5 gives M(X) = 10.8 ⇒ B. It’s true as boron generally exists in oxidation state III. X is B.
In water solution boron forms anionic oxo-species, the counter ion could be sodium as one of dominant ions in expelled water. The common boron mineral that contains sodium is borax Na2B4O7·10 H2O, it contains 11.3 mass % of boron.
X – B, Y – Na2B4O7 · 10 H2O.
Calculate the mass of Y that can be obtained from 1 L of expelled water.
Model Answer
The density of the diluted solution is 1 kg/L, then 1 ppm is 1 mg/L, 250 ppm is 250 mg of boron. The mass of borax is: m(Na2B4O7·10 H2O) = 250 / 0.113 = 2212 mg = 2.2 g.
The mass loss under gentle heating of Y is 37.8 %. Draw a possible structure of anion in Y, knowing that it contains two different types of X atoms (three- and four-coordinated).
Model Answer
The mass loss under gentle heating of borax is 37.8 % that corresponds to the loss of 8 water molecules.
The anion (H4B4O9)2– in Y contains two three-coordinated and two four-coordinated boron atoms: