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General Chemistry Principles, Patterns, and Applications, 2011

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The solubilities of all gases decrease with increasing temperature.<br />

The decrease in the solubilities of gases at higher temperatures has both practical <strong>and</strong> environmental<br />

implications. Anyone who routinely boils water in a teapot or electric kettle knows that a white or gray<br />

deposit builds up on the inside <strong>and</strong> must eventually be removed. The same phenomenon occurs on a<br />

much larger scale in the giant boilers used to supply hot water or steam for industrial applications, where<br />

it is called “boiler scale,” a deposit that can seriously decrease the capacity of hot water pipes (Figure 13.11<br />

"Boiler Scale in a Water Pipe"). The problem is not a uniquely modern one: aqueducts that were built by<br />

the Romans 2000 years ago to carry cold water from alpine regions to warmer, drier regions in southern<br />

France were clogged by similar deposits. The chemistry behind the formation of these deposits is<br />

moderately complex <strong>and</strong> will be described in more detail in Chapter 17 "Solubility <strong>and</strong> Complexation<br />

Equilibriums", but the driving force is the loss of dissolved CO2 from solution. Hard water contains<br />

dissolved Ca 2+ <strong>and</strong> HCO3 − (bicarbonate) ions. Calcium bicarbonate [Ca(HCO3)2] is rather soluble in water,<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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