Oxidation water

For chemical transformation of hydrogen-containing compounds with oxygen in many cases produced water . This water is called oxidation water . If this water is formed biochemically by living beings , the term metabolic water is also used .

Summary

Water balance of the kangaroo rat

When burning fossil fuels such as natural gas , crude oil or coal , e.g. B. in the internal combustion engine of a car, large amounts of water are always newly formed. The hydrocarbons of fossil fuels are oxidized (“burned”) together with the oxygen in the air, which mainly results in carbon dioxide and water. This newly formed water can be z. B. in a car on cool days (and cold engine) see in the form of clouds of steam coming out of the exhaust.

The oxidation water, which is produced by the breakdown of nutrients ( fats , carbohydrates and proteins ) in the cells of animals and humans in the cell metabolism, is of particular importance . This metabolic water is available to the whole body via the tissue fluids and the blood. In an adult human, it is assumed that around 250 to 300 ml of oxidation water are used per day  . In the case of many desert animals, this water contributes very significantly to the body's water supply, so that some species can survive for weeks without additional water intake (see adjacent figure and water balance ). One example is the genus of the kangaroo rats (Dipodymis), in which oxidation water covers up to 90% of the water balance.

Oxidation water in the energy metabolism

Example of glucose breakdown (dissimilation)

In both animals and plants, glucose (grape sugar) is the most important source of energy for cell metabolism. It is made available to human cells as blood sugar. With complete oxidative degradation, the well-known net equation of respiration (dissimilation) applies:

${\displaystyle \mathrm {C_{6}H_{12}O_{6}+6\ O_{2}\longrightarrow 6\ CO_{2}+6\ H_{2}O} }$

Glucose reacts with oxygen to form carbon dioxide and water.

The breakdown of 1 mol of glucose = 180 g leads to the formation of 6 mol of water = 6 · 18 g = 108 g of water. Per gram of degraded glucose, 108 g / 180 = 0.6 g of water is produced, i.e. about 0.6 ml.

Example fat loss

Fats (chemically triglycerides ) are very common reserve substances in plants in fruits, seeds and other parts of plants. Animals and humans store energy reserves in adipose tissue. To simplify matters, fat is equated with pure tripalmitine in the example calculation. If this fat is mobilized and completely oxidatively degraded, then the following net equation applies:

${\displaystyle \mathrm {2\ C_{51}H_{98}O_{6}+145\ O_{2}\longrightarrow 102\ CO_{2}+98\ H_{2}O} }$

Tripalmitin reacts with oxygen to form carbon dioxide and water.

So: 2 mol of tripalmitine = 2 · 807.35 g = 1614.7 g result in 98 mol of water = 98 · 18 g = 1764 g = 1.7 liters when completely broken down. So per gram of fat there is 1764 g / 1614.7 g = 1.092 g = approx. 1.1 ml of liquid oxidation water.

Oxidation water when burning fossil fuels

Crude oil and natural gas mainly consist of compounds containing hydrogen. When they are completely burned, a great deal of oxidation water is produced in addition to carbon dioxide. Hard coal, on the other hand, contains hardly any hydrogen compounds, so little water is produced - but all the more carbon dioxide. As an example, we want to estimate how much water is created when one liter of gasoline is burned. To simplify matters, gasoline is assumed to be pure octane (114 g · mol ⁻¹ ) with a density of 0.703 g · cm ⁻³ .

This gives the reaction equation:

${\displaystyle \mathrm {2\ C_{8}H_{18}+25\ O_{2}\longrightarrow 16\ CO_{2}+18\ H_{2}O} }$

Octane reacts with oxygen to form carbon dioxide and water.

From 2 mol octane = 2 114 g = 228 g, 18 mol water = (18 18 g) = 324 g. The combustion of 1 liter of octane = 703 g / 114 g = 6.1634 mol causes the formation of (6.1634 * 18 mol) / 2 = 998 g water, i.e. 1 liter of liquid water.

There is much discussion about the resulting carbon dioxide emissions because of its climate impact ( greenhouse effect ). In contrast, the influence of the water formed at the same time on the world climate is controversial or unclear. What is undisputed, however, is that water is a particularly effective greenhouse gas , far more effective than carbon dioxide . Since the water vapor content of the air ( relative humidity ) depends on the temperature and air pressure, the water content of the air changes significantly and the newly formed water is included in the water cycle. On the other hand, when the average temperature rises, the air absorbs more and more water vapor, which can lead to a positive feedback of the anthropogenic greenhouse effect ( run-away effect ). It will be discussed to what extent the expected increased cloud formation can counteract this influence.

literature

• KJ Ulrich: water balance . In: Wolf-Dieter Keidel : Brief textbook of physiology. Thieme Verlag, Stuttgart 1986, ISBN 3-13-358606-8 , chap. 11.1
• Stefan Silbernagl , Agamemnon Despopoulos : Pocket Atlas Physiology . Thieme Verlag, Stuttgart 2007, ISBN 978-3-13-567707-1 , p. 230f.
• Dieter Heinrich, Manfred Hergt: dtv-Atlas Ecology . Dtv, Munich 2003, ISBN 3-423-03228-6 , p. 100.
• Eduard Strasburger (greeting), Peter Sitte , Hubert Ziegler , Friedrich Ehrendorfer , Andreas Bresinsky (editing): Textbook of botany for universities . 34th edition Heidelberg 1999, ISBN 3-8274-0779-6 , p. 275.

Web links

• Why does a golden hamster have to drink little? (chemieunterricht.de)

Individual evidence

1. ↑ Knut Schmidt-Nielsen: How animals work . Cambridge University Press, 1972, ISBN 0-521-08417-2 , pp. 2 ( online [PDF]).