Weight/volume basis

In treated water for high-pressure boilers or where radiation effects are important, as in some nuclear projects, impurities are measured in very small units (e.g. g/litre or p.p. 10 ), but for most purposes it is convenient to express results in mg/litre. In water analysis, determinations (except occasionally for dissolved gases) are made on a weight/volume basis but some analysts still express results in terms of parts per million (p.p.m.). The difference between mg/litre and p.p.m. is small and for practical purposes the two units are interchtmgeable. For some calculations, the use of milli-equivalents per litre or equivalents per million (e.p.m.) has advantages but has not found much application. Hardness, whatever the constituent salts, is usually expressed as p.p.m. CaCOs (see Table 2.10). 

A key point to remember is that solutions of equal concentrations on a weight/ weight or weight/volume basis do not have the same number of molecules or reaction species, but solutions of thS" same molarity do. 

In the Trace Metals Project standard additions were used in all heated vaporization atomic absorption (HVAA) procedures. These procedures use sample aliquots of 10 /J or less consequently, a microstandard addition technique was developed. In this technique successive microliter aliquots of a /xg/ml standard are added to the sample solutions which have also been prepared on weight/volume basis. Since the volumes added or removed from the solution are negligible, the entire analysis is done on a single solution as detailed in the individual procedures. 

Calculate the final value as the average of the three values. The small volumes added to and removed from the sample solution during the analysis may be neglected in the calculation. Since both sample and standard are prepared on a weight/volume basis, the calculation is independent of the actual dilution used. The 5-ml volumetric flasks were convenient for the procedure. 

There are two basic ways to express the mass concentration of dissolved species (solutes) in solution. The first is to state concentration in units of mass of solute in a unit volume of solution—the so-called w/v (weight/ volume) basis, The second is a w/w basis, that is, weight of solute in a given weight of solution. Both of these methods of expressing concentration are widely used in water chemistry. For example, the units mg/liter and ppm (parts per million) are, respectively, the w/v and w/w units most often used to express the concentration of various materials in waters and wastewaters. They can be interconverted if the density of the solution is known. 

In practice, a master standard of component A and one of component C are prepared on a weight/volume basis in a solvent. Mixture of known volumes of each of these two standards can provide a variety of weight ratios of the two materials for the initial linearity check. The standard of component A can also be used to add a known amount of A to a known weight of sample. 

Geometric mean diameter (weight/volume basis)... 

In selecting a flame retardant for a given appHcation, the cost contribution of the flame retardant to the final polymer compound must be taken into account. Assessment of cost should be done on a cost per volume basis rather than a simple cost per weight basis. 

Capacity. Capacity is a measure of the quantity of ions, acid, or base removed (adsorbed) by an ion-exchange material. The quantity removed is direcdy correlated with the number of functional groups. Capacity is reported ia several different ways, but requites further definition because the word by itself does not cover ad situations. Total capacity is a measure of ad the functional groups on a resia and is recorded on a weight as wed as a volume basis. 

Concentration. The basis unit of concentration in chemistry is the mole which is the amount of substance that contains as many entities, eg, atoms, molecules, ions, electrons, protons, etc, as there are atoms in 12 g of ie, Avogadro s number = 6.0221367 x 10. Solution concentrations are expressed on either a weight or volume basis. MolaUty is the concentration of a solution in terms of the number of moles of solute per kilogram of solvent. Molarity is the concentration of a solution in terms of the number of moles of solute per Hter of solution. 

This is used most often in process plants. It is a tough, low-cost material with probably the widest range of chemical resistance of any of the low-cost plastics. On a volume basis, PVC is more favorable than polypropylene because the modulus of PVC is considerably higher than that of polypropylene, so it will form more rigid structures when used at the same thickness. On a weight basis it is not as favorable as PVC because it has a specific gravity of 1.4 compared with 0.92 for polypropylene. 

The abbreviations w/w and v/v are used to designate weight basis and volume basis. 

The results of the catalyst testing are shown in Table 3. The data listed in the table show, that on a per proton basis, catalyst A (based on 7% DVB) has higher activity as compared to resin materials, crosslinked with 12% DVB. This result is in accord with the finding by Petrus et al.,3 that at temperatures higher than 120 °C the hydration is under into particle diffusion limitation and as such, a more flexible polymeric matrix will provide better access to the acidic sites. On a dry weight basis, catalyst D showed the highest activity, which correlates well with the high acid site density found for this resin (Table 2). On a catalyst volume basis, catalyst A has the best performance characteristics followed by catalyst D. 

Particulate matter cannot be expressed on a volume-to-volume basis, but it can be expressed on a mole-per-unit-volume basis, M loles/m if the molecular weight is known. This would be a convenient unit to use in investigating the relationship between particles and gaseous species. 

The size designations are those given by Waters Associates. This set had a plate count of 680 PPF when o-dichlorobenzene was the solute. Samples were prepared on a weight-to-volume basis. Each sample was run at several different concentrations in the range of 0.05 - 0.2 g/dl in order to extrapolate the peak position to zero concentration. Full loop injections were used for all solutions. 

Laboratory results may be reported on an as received by volume basis or dry matter by mass basis, depending on whether the sample is considered to be a solid or a liquid. Samples >10% DM are generally treated as solids, and <10% DM as liquids. However, there are frequently exceptions to this rule, e.g. some fibrous samples <10% DM are difficult to pipette, so are analysed on a weight basis, but reported on a volume basis. Some customers can pump thick samples with >10% DM, so need the fertilizer values reported as liquids on a volume basis. Routine determination of density values facilitates calculation and reporting of fertilizer values in either mass or volume units. 

Because fuel and oil weights vary per standard volume, they should always be handled and sold on a weight basis, not volume basis. If sold on a volume basis, the volume should always be corrected to 60°F (15.5°C) by utilizing API volume reduction tables. These tables are used to standardize all volumes of petroleum products to a 60°F (15.5°C) volume. Standard API volume correction tables for petroleum products are contained in APPENDIX 3. 

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