Instruct: Given a question, retrieve documents that can help answer the question.
Query: What is the molecular weight of water?
Molecular masses are calculated from the standard atomic weights of each nuclide, while molar masses are calculated from the atomic mass of each element. The atomic mass takes into account the isotopic distribution of the element in a given sample (usually assumed to be "normal"). For example, water has a molar mass of 18.0153(3) g/mol, but individual water molecules have molecular masses which range between 18.010 564 6863(15) u (HO) and 22.027 7364(9) u (DO).
In everyday usage, mass and "weight" are often used interchangeably. For instance, a person's weight may be stated as 75 kg. In a constant gravitational field, the weight of an object is proportional to its mass, and it is unproblematic to use the same unit for both concepts. But because of slight differences in the strength of the Earth's gravitational field at different places, the distinction becomes important for measurements with a precision better than a few percent, and for places far from the surface of the Earth, such as in space or on other planets. Conceptually, "mass" (measured in kilograms) refers to an intrinsic property of an object, whereas "weight" (measured in newtons) measures an object's resistance to deviating from its natural course of free fall, which can be influenced by the nearby gravitational field. No matter how strong the gravitational field, objects in free fall are weightless, though they still have mass.
Schizophyllan has a molecular weight of 450,000 Da, and a specific rotation in water of +18-24°. A chemically analogous polysaccharide, scleroglucan, is formed by the fungus "Athelia rolfsii". Both polysaccharides share the chemical structure of the backbone with curdlan. It is known for several things, including its ability to stimulate the immune system, carry metals in water, aid in delivering drugs, and use in some nanofibers.
A hydrogen bond (H-bond), is a specific type of interaction that involves dipole-dipole attraction between a partially positive hydrogen atom and a highly electronegative, partially negative oxygen, nitrogen, sulfur, or fluorine atom (not covalently bound to said hydrogen atom). It is not a covalent bond, but instead is classified as a strong non-covalent interaction. It is responsible for why water is a liquid at room temperature and not a gas (given water's low molecular weight). Most commonly, the strength of hydrogen bonds lies between 0 - 4 kcal/mol, but can sometimes be as strong as 40 kcal/mol In solvents such as chloroform or carbontetrachloride one observes e.g. for the interaction between amides additive values of about 5 kJ/mol. According to L. Pauling the strength of a hydrogen bond is essentially determined by the electrostatic charges. Measurements of thousands complexes in chloroform or carbontetrachloride have led to additive free energy increments for all kind of donor-acceptor combinations.
The actual mass of an atom at rest is often expressed using the unified atomic mass unit (u), also called dalton (Da). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately . Hydrogen-1 (the lightest isotope of hydrogen which is also the nuclide with the lowest mass) has an atomic weight of 1.007825 u. The value of this number is called the atomic mass. A given atom has an atomic mass approximately equal (within 1%) to its mass number times the atomic mass unit (for example the mass of a nitrogen-14 is roughly 14 u). However, this number will not be exactly an integer except in the case of carbon-12 (see below). The heaviest stable atom is lead-208, with a mass of .
The basic SI unit of mass is the kilogram (kg). In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force.
Blood accounts for 7% of the human body weight, with an average density around 1060 kg/m, very close to pure water's density of 1000 kg/m. The average adult has a blood volume of roughly , which is composed of plasma and several kinds of cells. These blood cells (which are also called corpuscles or "formed elements") consist of erythrocytes (red blood cells, RBCs), leukocytes (white blood cells), and thrombocytes (platelets). By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%.
There are a variety of probes with different membrane and shaft length combinations available. The molecular weight cutoff of commercially available microdialysis probes covers a wide range of approximately 6-100kD, but also 1MD is available. While water-soluble compounds generally diffuse freely across the microdialysis membrane, the situation is not as clear for highly lipophilic analytes, where both successful (e.g. corticosteroids) and unsuccessful microdialysis experiments (e.g. estradiol, fusidic acid) have been reported. However, the recovery of water-soluble compounds usually decreases rapidly if the molecular weight of the analyte exceeds 25% of the membrane’s molecular weight cutoff.
Water has been detected in interstellar clouds within our galaxy, the Milky Way. Water probably exists in abundance in other galaxies, too, because its components, hydrogen and oxygen, are among the most abundant elements in the universe. Based on models of the formation and evolution of the Solar System and that of other star systems, most other planetary systems are likely to have similar ingredients.
The term "atomic weight" is being phased out slowly and being replaced by "relative atomic mass", in most current usage. This shift in nomenclature reaches back to the 1960s and has been the source of much debate in the scientific community, which was triggered by the adoption of the unified atomic mass unit and the realization that weight was in some ways an inappropriate term. The argument for keeping the term "atomic weight" was primarily that it was a well understood term to those in the field, that the term "atomic mass" was already in use (as it is currently defined) and that the term "relative atomic mass" might be easily confused with "relative isotopic mass" (the mass of a single atom of a given nuclide, expressed dimensionlessly relative to 1/12 of the mass of carbon-12; see section above).
Sodium chloride , also known as salt (though sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/mol respectively, 100 g of NaCl contains 39.34 g Na and 60.66 g Cl. Sodium chloride is the salt most responsible for the salinity of seawater and of the extracellular fluid of many multicellular organisms. In its edible form of table salt, it is commonly used as a condiment and food preservative. Large quantities of sodium chloride are used in many industrial processes, and it is a major source of sodium and chlorine compounds used as feedstocks for further chemical syntheses. A second major application of sodium chloride is de-icing of roadways in sub-freezing weather.
The atomic mass and relative isotopic mass are sometimes confused, or incorrectly used, as synonyms of standard atomic weight (also known as atomic weight) and the standard atomic weight (a particular variety of atomic weight, in the sense that is a standardized atomic weight). However, as noted in the introduction, atomic weight and standard atomic weight represent terms for (abundance-weighted) averages of atomic masses in elemental samples, not for single nuclides. As such, atomic weight and standard atomic weight often differ numerically from relative isotopic mass and atomic mass, and they can also have different units than atomic mass when this quantity is not expressed in unified atomic mass units (see the linked article for atomic weight).
The atomic mass or relative isotopic mass refers to the mass of a single particle, and therefore is tied to a certain specific isotope of an element. The dimensionless standard atomic weight instead refers to the average (mathematical mean) of atomic mass values of a typical naturally-occurring mixture of isotopes for a sample of an element. Atomic mass values are thus commonly reported to many more significant figures than atomic weights. Standard atomic weight is related to atomic mass by the abundance ranking of isotopes for each element. It is usually "about" the same value as the atomic mass of the most abundant isotope, other than what looks like (but is not actually) a rounding difference.
A hydrogen bond is a specific dipole where a hydrogen atom has a partial positive charge (δ+) to due a neighboring electronegative atom or functional group. Hydrogen bonds are amongst the strong intermolecular interactions know other than ion-dipole interactions. For intermolecular hydrogen bonds the δ+ hydrogen interacts with a δ- on an adjacent molecule. Examples of molecular solids that hydrogen bond are water, amino acids, and acetic acid. For acetic acid, the hydrogen (δ+) on the alcohol moiety of the carboxylic acid hydrogen bonds with other the carbonyl moiety (δ-) of the carboxylic on the adjacent molecule. This hydrogen bond leads a string of acetic acid molecules hydrogen bonding to minimize free energy. These strings of acetic acid molecules then stack together to build solids.
To qualify as a metabolite, or to be considered to be part of the metabolome, a small molecule must typically have a molecular weight <1500 Da. This means that molecules such as glycolipids, polysaccharides, short peptides (<14 amino acids) and small oligonucleotides (<5 bases) can be regarded as metabolites or constituents of the metabolome. On the other hand, very large macromolecules such as proteins, messenger RNA, ribosomal RNA, microRNA and DNA are definitely not metabolites and are not considered to be part of the metabolome. The study of the metabolome is called metabolomics.
Chloropicrin's chemical formula is CClNO and its molecular weight is 164.38 grams/mole. Pure chloropicrin is a colorless liquid, with a boiling point of 112 °C. Chloropicrin is sparingly soluble in water with solubility of 2000 mg/L at 25 °C. It is volatile, with a vapor pressure of 23.2 millimeters of mercury (mmHg) at 25 °C; the corresponding Henry's law constant is 0.00251 atmosphere-cubic meter per mole. The octanol-water partition coefficient ("K") of chloropicrin is estimated to be 269. Its soil adsorption coefficient ("K"; normalized to soil organic matter content) is 25 cm/g.
Any substance consisting of two or more different types of atoms (chemical elements) in a fixed stoichiometric proportion can be termed a "chemical compound"; the concept is most readily understood when considering pure chemical substances. It follows from their being composed of fixed proportions of two or more types of atoms that chemical compounds can be converted, via chemical reaction, into compounds or substances each having fewer atoms. The ratio of each element in the compound is expressed in a ratio in its chemical formula. A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using the standard abbreviations for the chemical elements, and subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is HO. In the case of non-stoichiometric compounds, the proportions may be reproducible with regard to their preparation, and give fixed proportions of their component elements, but proportions that are not integral [e.g., for palladium hydride, PdH (0.02 < x < 0.58)].
A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using the standard abbreviations for the chemical elements, and subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is HO. Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service (CAS): its CAS number.
The scientists brought with them 26 cans containing of heavy water worth ₤22,000. Originally from Norway, it was a vital ingredient in nuclear energy research that would find use in the British Tube Alloys project. The managing director of the Antwerp Diamond Bank, Paul Timbal, joined them, bringing with him between ₤1 million and ₤3 million in diamonds. They also discovered of machine tools in wagons on the quay, which were loaded on board. The diamonds and the heavy water were strapped to the deck on wooden pallets, so that if the ship was sunk they might float free, and possibly be recovered. On 19 June, "Broompark" weighed anchor and sailed down the Gironde estuary without the assistance of a pilot or tug boats, and made its way safely to Falmouth, arriving on 21 June.
A human being can survive an average of three to five days without the intake of water. The issues presented by the need for water dictate that unnecessary water loss by perspiration be avoided in survival situations. The need for water increases with exercise.
There are two conventions regarding the "standard boiling point of water": The "normal boiling point" is at a pressure of 1 atm (i.e., 101.325 kPa). The IUPAC recommended "standard boiling point of water" at a standard pressure of 100 kPa (1 bar) is . For comparison, on top of Mount Everest, at elevation, the pressure is about and the boiling point of water is .
The Celsius temperature scale was defined until 1954 by two points: 0 °C being defined by the water freezing point and 100 °C being defined by the water boiling point at standard atmospheric pressure.
Mass (m) per unit volume (V) is the density m/V. Mass is conserved on mixing, but the volume of 1 cm of ethanol mixed with 1 cm of water is reduced to less than 2 cm due to the formation of ethanol-water bonds. The plot of volume or density versus molecular fraction of ethanol in water is a quadratic curve. However, the plot of index of refraction versus molecular fraction of ethanol in water is linear, and the weight fraction equals the fractional density (d; Teertstra 2005).
In chemistry, the molar mass "M" is a physical property defined as the mass of a given substance (chemical element or chemical compound) divided by the amount of substance. The base SI unit for molar mass is kg/mol. However, for historical reasons, molar masses are almost always expressed in g/mol.
A molecule of heavy water has two deuterium atoms in place of the two protium atoms of ordinary "light" water. The weight of a heavy water molecule, however, is not substantially different from that of a normal water molecule, because about 89% of the molecular weight of water comes from the single oxygen atom rather than the two hydrogen atoms. The colloquial term "heavy water" refers to a highly enriched water mixture that contains mostly deuterium oxide , but also some hydrogen-deuterium oxide (HDO) and a smaller amount of ordinary hydrogen oxide . For instance, the heavy water used in CANDU reactors is 99.75% enriched by hydrogen atom-fraction—meaning that 99.75% of the hydrogen atoms are of the heavy type. For comparison, ordinary water (the "ordinary water" used for a deuterium standard) contains only about 156 deuterium atoms per million hydrogen atoms, meaning that 0.0156% of the hydrogen atoms are of the heavy type.
The molar mass of atoms of an element is given by the Standard atomic weight of the element multiplied by the molar mass constant, "M" = 1 × 10 kg/mol = 1 g/mol:
Multiplying by the molar mass constant ensures that the calculation is dimensionally correct: standard relative atomic masses are dimensionless quantities (i.e., pure numbers) whereas molar masses have units (in this case, grams/mole).