Air Composition

Dry air contains nitrogen 78.048%, oxygen 20.9476%, argon 0.9347%, carbon dioxide 0.0314%, hydrogen 0.00005%. The composition of gas mixture is expressed as volume percent. The remaining 0.01 percent is accounted for by traces of neon, krypton, helium, ozone and xenon.

Science: Is air a compound or a mixture?

Air is the mixture of gases. The composition of gas mixtures is always expressed as volume percent unless otherwise specified. For a mixture of given composition, the volume occupied by each individual component may be computed by knowing the total volume, the partial pressure of each component may be computed by knowing the total pressure and the number of moles of each component may be calculated by knowing the total number of moles percent.

In many calculations, including gas mixtures, it is desired to know pseudo (or average) molecular mass of a mixture. The mixture of gases known as air enters into so many engineering problems that it is desirable to know its composition and pseudomolecular mass. Dry air contains nitrogen 78.048%, oxygen 20.9476%, argon 0.9347%, carbon dioxide 0.0314%, hydrogen 0.00005%. The composition of gas mixture is expressed as volume percent. The remaining 0.01 percent is accounted for by traces of neon, krypton, helium, ozone and xenon.

For most engineering calculations, air is assumed to have a composition of 79% nitrogen and 21% oxygen with the principal minor constituent, argon, being considered to be nitrogen. Air will contain water vapor but the amount will depend on weather conditions. The pseudomolecular mass of air may be calculated to be approximately 29 lb-mass per lb-mole and this figure should be used in problems involving air.

The calculation to get the psedomolecular mas of air,

Air Composition            Molecular mass (lb-mass per lb-mole)

N2 78.048%                   28.02
O2 20.9476%                 32.00
CO2 0.0314%,                44.00
H2 0.00005%                 2.02
Ar 0.9347%,                    39.91

Pseudomolecular mass of air = (28.02 x 0.78084) + (32 x 0.209476) + (44 x 0.000314) + (2.02 x 0.0000005) + (39.91 x 0.009347)

= 28.969 ~ 29 lb-mass per lb-mole

1. A mixture.The difference between a compound and a mixture is primarily that a mixture can be separated through physical means. Since air is essentially just a collection of various gases, air is a mixture.

2. Air is known to be a type of mixture. The very air that we have in the planet is actually a mixture of various gases that are naturally present in the world. A lot of calculations were made in order to confirm this, and there is a decent explanation to this that might pique your interests as well.

The actual mixture of the component were calculated over and over again, but the results are not exact, rather estimated to be exact. The molecular mixture of the gases ultimately formed the air that we breathe. Take note that this type of air is still made up of oxygen, but it’s not just any ordinary type of oxygen as it contains various components that made it more breathable as well.

It’s said that air is known to be also made up of nitrogen, and most of its components are actually nitrogen – with oxygen providing at least 20% of it. Other components are a very small fraction of argon and an very, very tiny amount of hydrogen. Scientists are not sure if there are any other components mixed into the fresh air that we breathe, but these four elements are the main ones that made up the air that we have.

Compounds, on the other hand, are known to have a more fixed amount than mixtures – just like how we mix water with a flavoring that we want. Compounds always needed to be exact, and therefore, air is actually a mixture of various elements in a natural way, but also in a way where it’s perfect for us to breathe in and out.

 

A chemical compound is a chemical substance consisting of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition.

The ratio of each element is usually expressed by chemical formula.
For example, water (H2O) is a compound consisting of two hydrogen atoms bonded to an oxygen atom.
The atoms within a compound can be held together by a variety of interactions, ranging from covalent bonds to electrostatic forces in ionic bonds.
A continuum of bond polarities exist between the purely covalent bond (as in H2) and ionic bonds.
For example H2O is held together by polar covalent bonds.
Sodium chloride is an example of an ionic compound.

3. Pure air is actually a solution of the gases in the relative ratios listed in many of the previous posts. It is also a mixture in a practical sense, since the air we actually breathe contains numerous very small particles of dust, other organic particles, water droplets, etc.

4. Air is a mixture, which is made up of different compounds (covalently bound molecules made up of different elements, such as water H2O), and elements (molecules  made of only one element, like O2, and H2 or individual atoms). To further complicate the name game, air is also a solution, which is a homogeneous mixture (all one phase, gaseous in this instance). A solution is a type of mixture.

5. Air is a mixture of elements such as Oxygen and Nitrogen and a mixture of compounds such as water and carbon dioxide. A mixture is something that can be separated through physical means. Air can be separated into its elements and compounds by fractional distillation.

6. The best reason I can think of for why we believe that air is a mixture is that freezing air slowly yields different liquids at different temperatures. Liquid nitrogen has a different boiling point than liquid oxygen. They also freeze at different temperatures. If air were only 1 compound, then air in its entirety would have a single boiling point and a single freezing point.

7. Air is a mixture/blend of several gases and water (moisture). Its composition may change based on the ambient conditions. It is because it can be separated to its components using separation methods. Air is Mixture of nitrogen, oxygen, argon and trace gasses.

8. It is a mixture of several compounds, mainly nitrogen and oxygen with bits of water vapour, carbon dioxide and argon, plus traces of many other gases.

Is a mixture of air and liquid air a pure substance?

1.Air itself is not a ‘pure substance’. Air is a mixture— primarily of nitrogen and oxygen, plus small amounts of a handful of other things (CO2, Argon, etc, etc). Anything that is a ‘mixture’ is by definition not a ‘pure substance’.

Thank you very much.

2.No, because relative proportions of oxygen and nitrogen differs in air (gaseous phase) and liquid air (liquid phase) in equilibrium.

Since, pure substance is homogeneous and invariable in chemical composition. Moreover relative proportion of chemical elements of substance is constant. Therefore, not a pure substance.

          
     

Markers of hydration status

S M Shirreffs

¹School of Sport and Exercise Sciences, Loughborough University, Leicestershire, UK

 

Correspondence: SM Shirreffs, School of Sport and Exercise Sciences, Loughborough University, Leicestershire LE11 3TU, UK. E-mail: s.shirreffs@lboro.ac.uk

Guarantor: SM Shirreffs.

Abstract

Many indices have been investigated to establish their potential as markers of hydration status. Body mass changes, blood indices, urine indices and bioelectrical impedance analysis have been the most widely investigated. The current evidence and opinion tend to favour urine indices, and in particular urine osmolality, as the most promising marker available.

Keywords: hydration status, water balance, euhydration, hypohydration

Hydration status—some definitions

Euhydration is the state or situation of being in water balance. However, although the dictionary definition is an easy one, establishing the physiological definition is not so simple. Hyperhydration is a state of being in positive water balance (a water excess) and hypohydration the state of being in negative water balance (a water deficit). Dehydration is the process of losing water from the body and rehydration the process of gaining body water. Euhydration, however, is not a steady state, but rather is a dynamic state in that we continually lose water from the body and there may be a time delay before replacing it or we may take in a slight excess and then lose this (Greenleaf, 1992).

Water intake and loss

The routes of water loss from the body are the urinary system via the kidney, the respiratory system via the lungs and respiratory tract, via the skin, even when not visibly sweating, and the gastrointestinal system as faeces or vomit. The routes of water gain into the body are gastro intestinally from food and drink consumption and due to metabolic production. Many textbooks, both recent and older, state water gain and loss figures for the average sedentary adult in a moderate environment in the order of 2550 ml (McArdle et al, 1996), 2600 ml (Astrand & Rodahl, 1986) and 2500 ml (Diem, 1962). However, it is interesting to note that the source of this data is never given.

Measurement of total body water

The body water content of an individual can be measured or estimated in a number of ways, but the current consensus is that tracer methodology gives the best measure of total body water. Deuterium oxide (D₂O or ²H₂O) is the most commonly used tracer for this purpose and full details of the methods and protocols, assumptions and limitations are well discussed elsewhere (Schoeller, 1996). Briefly, the tracers are distributed relatively rapidly in the body (in the order of 3–4 h for an oral dose) and correction can be made for exchange with non-aqueous hydrogen. It is estimated that total body water can be measured with a precision and accuracy of 1–2%.

Assessing hydration status

Hydration status has been attempted to be assessed in a variety of situations for a number of years. In 1975, Grant and Kubo divided the tests open to use in a clinical setting into three categories: laboratory tests, objective noninvasive measurements and subjective observations. The laboratory tests were measures of serum osmolality and sodium concentration, blood urea nitrogen, haematocrit and urine osmolality. The objective, noninvasive measurements included body mass, intake and output measurements, stool number and consistency and 'vital signs', for example, temperature, heart rate and respiratory rate. The subjective observations were skin turgor, thirst and mucous membrane moisture. This manuscript concluded that, although the subjective measurements were least reliable, in terms of consistency of measurement between measurers, they were the simplest, fastest and most economical. The laboratory tests were deemed to be the most accurate means to assess a patient's hydration status. Since this manuscript was published, there has been a large amount of research into some of these measurements, observations and tests, and some of the main ones, along with others, are discussed in the rest of this paper.

Body mass

Acute changes in body mass over a short time period can frequently be assumed to be due to body water loss or gain; 1 ml of water has a mass of 1 g (Lentner, 1981) and therefore changes in body mass can be used to quantify water gain or loss. Over a short time period, no other body component will be lost at such a rate, making this assumption possible.

 

Throughout the exercise literature, changes in body mass over a period of exercise have been used as the main method of quantifying body water losses or gains due to sweating and drinking. Indeed, this method is frequently used as the method to which other methods are compared. Respiratory water loss and water exchange due to substrate oxidation are sometimes calculated and used to correct the sweat loss values, but this is not always done (Mitchell et al, 1972). Examples of such types of calculations are shown in Table 1.

 

Table 1. Examples of hydration status calculations

Figure and tables index

Exercise	Pre-exercise Body mass a (kg)	Post-exercise Body mass b (kg)	Total body massloss or gain a (ml or g)	Drinks consumed during exercise b (ml)	Urine excreted during exercise c (ml)	Sweat volume (ml)	Hydration status d (%)
60 min Running	70.00	68.00	-2000	0	200	1800	-2.9
3 h Walking	70.00	70.00	0	500	400	100	0.0
2 h Cycling	70.00	70.20	+200	1000	0	800	+0.3

^a Body mass measured nude with dry skin.
^b Drinks consumed any time between the two body mass measurements.
^c Urine emptied from the bladder any time between the two body mass measurements.
^d +=water gain, -=water loss, 0=no change in water balance.

Blood indices

Collection of a blood sample for subsequent analysis has been both investigated and used as a hydration status marker.

Measurement of haemoglobin concentration and haematocrit has the potential to be used as a marker of hydration status or change in hydration status, provided a reliable baseline can be established. In this regard, standardisation of posture for a time prior to blood collection is necessary to distinguish between postural changes in blood volume, and therefore in haemoglobin concentration and haematocrit, which occur (Harrison, 1985) and change due to water loss or gain.

 

Plasma or serum sodium concentration and osmolality will increase when the water loss inducing dehydration is hypotonic with respect to plasma. An increase in these concentrations would be expected, therefore, in many cases of hypohydration, including water loss by sweat secretion, urine production or diarrhoea. However, in subjects studied by Francesconi et al (1987), who lost more than 3% of their body mass mainly through sweating, no change in haematocrit or serum osmolality was found, although as described below certain urine parameters did show changes. Similar findings to this were reported by Armstrong et al (1994, 1998). This perhaps suggests that plasma volume is defended in an attempt to maintain cardiovascular stability, and so plasma variables will not be affected by hypohydration until a certain degree of body water loss has occurred.

 

Plasma testosterone, adrenaline and cortisol concentrations were reported by Hoffman et al (1994) not to be influenced by hypohydration to the extent of a body mass loss of up to 5.1% induced by exercise in the heat. In contrast, however, plasma noradrenaline concentration did respond to the hydration changes, which means that it may be possible to use this as a marker of hydration status, at least when induced by exercise in the heat.

Urine indices

Collection of a urine sample for subsequent analysis has also been investigated and used as a hydration status marker.

 

Measurement of urine osmolality has recently been an extensively studied parameter as a possible hydration status marker. In studies of fluid restriction, urine osmolality has increased to values greater than 900 mosm/kg for the first urine of the day passed in individuals dehydrated by 1.9% of their body mass, as determined by body mass changes (Shirreffs & Maughan, 1998). Armstrong et al (1994) have determined that measures of urine osmolality can be used interchangeably with urine-specific gravity, opening this as another potential marker.

 

Urine colour is determined by the amount of urochrome present in it (Diem, 1962). [*u·ro·chrome[yóorə krṑm] is a yellow pigment that gives urine its normal color]

 

 

 

 

 

 When large volumes of urine are excreted, the urine is dilute and the solutes are excreted in a large volume. This generally gives the urine a very pale colour. When small volumes of urine are excreted, the urine is concentrated and the solutes are excreted in a small volume. This generally gives the urine a dark colour. Armstrong et al (1998) have investigated the relationship between urine colour and specific gravity and conductivity. Using a scale of eight colours (Armstrong, 2000), it was concluded that a linear relationship existed between urine colour and both specific gravity and osmolality of the urine, and that urine colour could therefore be used in athletic or industrial settings to estimate hydration status when a high precision may not be needed.

 

Urine indices of hydration status perhaps have their limitation in identifying changes in hydration status during periods of rapid body fluid turnover, as in subjects studied who lost approximately 5% of their body mass with, on average, 62 min of exercise in the heat, then rehydrating by replacing this lost fluid (Popowski et al, 2001). In these subjects, in comparison to measures of plasma osmolality which increased and decreased in an almost linear fashion, urine osmolality and specific gravity were found to be less sensitive and demonstrated a delayed response, lagging behind the plasma osmolality changes.

Bioelectrical impedance analysis

Bioelectrical impedance analysis (BIA) has been widely investigated as a tool for assessing body composition. It has the potential to assess hydration status by the determination of body water and its cellular divisions if a multifrequency device is used. In multifrequency BIA, a current is applied at different frequencies and the higher conductivity of water compared to the other compartments is used to determine its volume. The National Institute of Health technology assessment statement (National Institute of Health, 1994) concluded that 'BIA provides a reliable estimate of total body water under most conditions.' It carried on to state that 'BIA values are affected by numerous variables including... hydration status' and that 'Reliable BIA requires standardisation and control of these variables.' Subsequent work in this area has generally highlighted the limitations of the technique. For example, Asselin et al (1998) concluded that with acute dehydration and rehydration of 2–3% of body mass, standard equations failed to predict changes in total body water, as determined by changes in body mass. Saunders et al (1998) reported that small body water changes were reported as body fat changes in an athletic population, and Berneis and Keller (2000) after inducing extracellular volume and tonicity alterations by infusion and drinking concluded that BIA may not be reliable.

Other markers

Hydration status has also been investigated by a number of less commonly investigated parameters. For example, alterations in the response of pulse rate and systolic blood pressure to postural change have been demonstrated in clinical settings of dehydration and rehydration (Johnson et al, 1995). The diameter of the inferior cava vein, measured with the subject lying supine, has been used with patients undergoing peritoneal dialysis (Cheriex et al, 1989).

Conclusions

The body water content of a person is most appropriately determined using tracer methodology with the use of deuterium oxide. The determination of a person's hydration status has received increasing attention over the past 10 years, much of it influenced by body water losses that can occur in a relatively short period of time with physical activity. Blood-borne parameters and urinary markers have been widely studied areas, with a substantial amount of research into the use of BIA also being undertaken. In most cases, acute changes in body mass are used to signify the body water losses or gains to which comparisons are made. However, an arbitrary decision or definition of euhydration must be made before a person is assigned to being in a state of hypohydration or hyperhydration, and this perhaps remains a major issue to be resolved.

 

The choice of hydration status marker will ultimately be determined by the sensitivity and accuracy with which hydration status needs to be established, the technical and time requirements and the expense of the method. However, consideration must also be given to other conditions or complicating factors that may impact on the parameter of measurement.

 

From the studies reviewed above, it seems fair to conclude that urinary measures are more sensitive than the other methods, but they may have a time lag over the short term. It must also be remembered that classification of the state of hypohydration or hyperhydration depends on the physiological definition of euhydration, which is not as simple as giving the dictionary definition.

References

1. Armstrong LE (2000): Performing in Extreme Environments. Champaign: Human Kinetics.
2. Armstrong LE, Soto JA, Hacker Jr FT, Casa DJ, Kavouras SA & Maresh CM (1998): Urinary indices during dehydration, exercise, and rehydration. Int. J. Sport Nutr. 8, 345–355.
3. Armstrong LE, Maresh CM, Castellani JW, Bergeron MF, Kenefick RW, LaGasse KE & Riebe D (1994): Urinary indices of hydration status. Int. J. Sport Nutr. 4, 265–279.
4. Asselin M-C, Kriemler S, Chettle DR, Webber CE, Bar-Or O & McNeill FE (1998): Hydration status assessed by multi-frequency bioimpedance analysis. Appl. Radiat. Isot. 49, 495–497.
5. Astrand PO & Rodahl K (1986): Textbook of Work Physiology. p 619. Singapore: McGraw-Hill International.
6. Berneis K & Keller U (2000): Bioelectrical impedance analysis during acute changes of extracellular osmolality in man. Clin. Nutr. 19, 361–366.
7. Cheriex EC, Leunissen KML, Janssen JHA, Mooy JMV & van Hooff JP (1989): Echography of the inferior vena cava is a simple tool for estimation of 'dry weight' in hemodialysis patients. Nephrol. Dial. Transpl. 4, 563–568.
8. Diem K (1962): Documenta Geigy Scientific Tables. pp 538–539. Manchester: Geigy Pharmaceutical Company Limited.
9. Francesconi RP, Hubbard RW, Szlyk PC, Schnakenberg D, Carlson D, Leva N, Sils I, Hubbard L, Pease V, Young J & Moore D (1987): Urinary and hematological indexes of hydration. J. Appl. Physiol. 62, 1271–1276.
10. Greenleaf JE (1992): Problem: thirst, drinking behaviour, and involuntary dehydration. Med. Sci. Sports Exerc. 24, 645–656. | PubMed | ISI | ChemPort |
11. Harrison MH (1985): Effects of thermal stress and exercise on blood volume in humans. Physiol. Rev. 65, 149–209.
12. Hoffman JR, Maresh CM, Armstrong LE, Gabaree CL, Bergeron MF, Kenefick RW, Castellani JW, Ahlquist LE & Ward A (1994): Effects of hydration state on plasma testosterone, cortisol, and catecholamine concentrations before and during mild exercise at elevated temperature. Eur. J. Appl. Physiol. 69, 294–300.
13. Johnson DR, Douglas D, Hauswald M & Tandberg D (1995): Dehydration and orthostatic vital signs in women with hyperemesis gravidarum. Acad. Emer. Med. 2, 692–697.
14. Lentner C (1981): Geigy scientific tables. 8th Edition. Basle: Ciba-Geigy Limited.
15. McArdle WD, Katch FI & Katch VL (1996): Exercise Physiology: Energy, Nutrition, and Human Performance. p 54. Philadelphia: Lippincott Williams & Wilkins.
16. Mitchell JW, Nadel ER & Stolwijk JAJ (1972): Respiratory weight losses during exercise. J. Appl. Physiol. 32, 474–476. | PubMed | ISI | ChemPort |
17. National Institutes of Health (1994): Bioelectrical impedance analysis in body composition measurement. NIH Technol. Assess. Statement. December 12–14, pp 1–35.
18. Popowski LA, Oppliger RA, Lambert GP, Johnson RF, Johnson AK & Gisolfi CV (2001): Blood and urinary measures of hydration status during progressive acute dehydration. Med. Sci. Sports Exerc. 33, 747–753.
19. Saunders MJ, Blevins JE & Broeder CE (1998): Effects of hydration changes on bioelectrical impedance in endurance trained individuals. Med. Sci. Sports Exerc. 30, 885–892.
20. Schoeller DA (1996): Hydrometry. In Human Body Composition. eds A Roche, S Heymsfield & T Lohman, pp 25–43. Champaign: Human Kinetics.
21. Shirreffs SM & Maughan RJ (1998): Urine osmolality and conductivity as indices of hydration status in athletes in the heat. Med. Sci. Sport Exerc. 30, 1598–1902

Water Electrolysis,

What does salt do in the electrolysis of water?

Salt acts as a conductor of electricity in the electrolysis of water. Table salt is called an electrolyte, meaning it can be decomposed into its ions through electrolysis.

Electrolysis is a method of separating molecular compounds, such as water, into their constituent elements by passing an electric current through them. Each molecule of these compounds is bonded together by electrons. When table salt is dissolved in water, its ions are released into the solution. When an electric current is passed through the solution by the immersion of positively and negatively charged electrodes, these sets of positive and negative ions are each attracted to an oppositely charged electrode. As the ions gather around each electrode, electrons are absorbed or released, leading to the breakdown of water into hydrogen and oxygen.


Where does salt come from?


Salt that is used for a variety of industrial and food-related purposes comes primarily from shallow bodies of sea or mineral water and from mining operations dedicated to salt production. The method of production is determined by the location from which the salt is harvested. Location and method also determine the type of salt sold as a final product as well as its intended use.

The three methods of industrial salt production are solution mining, deep-shaft mining and solar evaporation. Most table and industrial salt is produced by solution mining, whereby water is injected into massive deposits of salt forced to the surface of the Earth by tectonic pressures. The water dissolves the salt into a solution, called brine, which is then pumped out and dehydrated at another location.

In deep-shaft mining, or conventional mining, tunnels are dug underground to reach the salt leftover from ancient sea beds, which is then mined like any other mineral. This primarily results in rock salt. The purest salt, however, is harvested through solar evaporation. In warm regions with low rates of precipitation, salt is harvested once a year from shallow ponds and pools evaporated by the sun during the summer. Salt produced in this fashion, called “sea salt,” is a common ingredient in cooking and cosmetics.