Volume common units

Density Why is it easier to lift a backpack filled with gym clothes than the same backpack filled with books The answer can be thought of in terms of density—the book-filled backpack contains more mass in the same volume. Density is a physical property of matter and is defined as the amount of mass per unit volume. Common units of density are grams per cubic centimeter (g/cm ) for solids and grams per milliliter (g/mL) for liquids and gases. 

The quantity of a solute adsorbed can be given conveniently in terms of moles or volume (for adsorption) or ion-equivalents (for ion exchange) per unit mass or volume (dry or wet) of sorbent. Common units for adsorption are moV(m of fluid) for the fluid-phase concentration Cj and moV(kg of clean adsorbent) for adsorbed-phase concentration /ij. For gases, partial pressure may replace concentration. 

The density of a substance is commonly calculated in chemistry. The density (D) of an object is calculated by dividing the mass of the object by its volume. (Some authors will use a lowercase d to represent the density term be prepared for either.) Since density is independent of the quantity of matter (a big piece of gold and a little piece have the same density), it can be used for identification purposes. The most common units for density in chemistry are g/cm3 or g/mL. 

The catalytic action of an enzyme, its activity, is measured by determining the increase in the reaction rate under precisely defined conditions—i.e., the difference between the turnover (violet) of the catalyzed reaction (orange) and uncatalyzed reaction (yellow) in a specific time interval. Normally, reaction rates are expressed as the change in concentration per unit of time (mol 1 s see p. 22). Since the catalytic activity of an enzyme is independent of the volume, the unit used for enzymes is usually turnover per unit time, expressed in katal (kat, mol s ). However, the international unit U is still more commonly used (pmol turnover min 1 U = 16.7 nkat). 

The other common unit for liquid solutions is molality, the number of moles of solute in 1 kilogram of solvent. Molality contrasts with molarity because it reports the amount of solute relative to the mass of the solvent, not the volume of the solution. A 2 molal solution of hydrogen fluoride, abbreviated 2 m (with a lowercase m for distinction from molarity), contains 2 moles of HF (40.02 grams) dissolved in 1,000 grams of H2O. Molality is the preferred unit for certain types of calculations, although it is used less in laboratory work. 

It is quite common practice to express concentrations as a ratio, using the parts per method of describing the ratio. Thus, in soil the ratio is simple, 1 ng/g, or (10 9 g/g), is a ppb, or one part per billion5. In water or air, the issue is a bit more complex since it is necessary to reconcile the units of mass per unit volume to units of mass per unit mass. We make this reconciliation by dividing by the density of the fluid. For water this is, for purposes of this book, taken as... 

For atmospheric particulate matter, concentrations are expressed in mass per unit volume, commonly fig m 3, or in the number of particles per unit volume, for example, per cm3. 

The most common unit of <2rel is bed volumes per hour (BV/li). Space velocity is also used in catalytic reactors, especially in three-phase fixed-beds, and is referred to as liquid hourly space velocity (LHS V) for the liquid phase, and gas hourly space velocity (GHSV) for gas phase. As mentioned above, space-time and space velocity are measured under the entrance conditions. However, for space velocity, other conditions are frequently used (Fogler, 1999). For example, the LHSV is measured at 60 to 75 °F, and GHSV at standard temperature and pressure. 

The units for Cp can vary. The most common units are in the form of mass/volume, such as pg/mL or ng/mL. This chapter exclusively uses Cp with mass/volume units. Very rarely, Cp is encountered in the chemist-familiar moles/volume format like pM or nM. 

Analyte concentrations expressed in ppm or ppb do not provide an indication of whether a solid or a liquid sample was analyzed or whether a sample was prepared for analysis by weight or by volume. These units should not be used when reporting results of soil and water analyses. However, they are commonly (and correctly) used... 

Weight per volume. The units most commonly used are milligram per liter (mg/1), for major ions, and microgram per liter (pg/1), for trace elements. For example, data for groundwater from the Uriya 3 well are given in Table 5.2 in weight per volume units. 

The units of all terms of this equation must be the same. The product PV has the units of energy, as does U therefore H also has units of energy. In the SI system the basic unit of pressure is the pascal or N m"2 and, for volume, the m3. Thus the PV product has the unit N m or joule. In the English engineering system a common unit for the PV product is the (ft lbr), which arises when pressure is in (lbr)(ft) 2 with volume in (ft)3. This result is usually converted to (Btu) through division by 778.16 for use in Eq. (2.6), because the common English engineering unit for U and H is the (Btu). 

A number of applications are given in this chapter that detail the capture and recovery of intracellular proteins including recombinant proteins. The initial protein recovery steps, regardless of the source, are usually associated with large volumes and crude solutions, requiring removal of particles and reduction of volume before their purification can take place. Centrifugation, filtration, precipitation, solvent extraction, and batch adsorption are common unit operations involved in the preliminary steps of protein recovery. Expanded-bed adsorption, as described here, is an approach for the initial protein recovery that eliminates the need for clarification and volume reduction. In this process, a crude starting solution is pumped directly onto an... 

Another common unit of measurement for natural gas is by use of its heating value, expressed in British thermal units (BTU) per standard cubic foot in the English system, and in Joules (or calories) per unit volume in the metric system. Commercially used natural gas, after processing, yields the equivalent of about 950-1050 BTU/ft3. Also used as a unit of measurement is the therm, equivalent to 100,000 BTU, or the nominal heat content of 100 standard cubic feet of lean, processed natural gas. 

The most common unit of measurement in the English system is the mcf or thousand (103) cubic feet. Larger volumes, used to express production or pipeline volumes, are noted as bcf, or billion (109) cubic feet. Even larger volumes, such as reserve figures, usually are expressed as tcf, or trillion (1012) cubic feet. 

In the petroleum business it is common to report flow rates in standard volumes per unit time. 

Where present, the sole purpose of a sample spreading function is rapid lateral spreading of a sample after application (5). This feature mediates a uniform sample volume per unit volume of the element (Fig. 2). Substances commonly used to construct spreading functions include fabrics, membranes, and paper. 

In SI units (p. 71) the concentration of a solute is expressed in molm , which is essential for calculating specific parameters for substances (e.g. p. 73), but which is inconvenient when dealing with solutions in the laboratory. A cubic metre (m ) of water weighs approximately 1 ton A common unit of volume used in chemistry is the litre (L) this is a non-SI unit and is converted to the SI unit of volume (m ) using 1.0 L = 10 m. The concentration of a solute is usually symbolized by square brackets, e.g. [NaCl]. Details of how to prepare solutions are given on pp. 17, 19. 

As you have learned, percent by volume and percent by mass are only two of the commonly used ways to quantitatively describe the concentrations of liquid solutions. One of the most common units of solution concentration is molarity. Molarity (M) is the number of moles of solute dissolved per hter of solution. Molarity also is known as molar concentration. The unit M is read as molar. A liter of solution containing one mole of solute is a IM solution, which is read as a one molar solution. A liter of solution containing 0.1 mole of solute is a 0.1 M solution. 

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