Amount concentrations in aquatic chemistry (original) (raw)
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Concentration scales: a plea for physico-chemical data
Marine Chemistry, 1976
The four scales considered are molal (m, γ, mol/kg-water), molar (c, y, mol/dm3), mole fraction (x, f, mol/total-moles), and the uniquely oceanographic scale - for which nomenclature is proposed - ‘mokal’ (k, v, mol/kg-seawater). Conversion ratios are given in tabular form for multi-component ionic mixtures and as functions of salinity. Conversion of concentrations, activity coefficients, activities, Debye-Hückel ‘constants’, and ionization functions is treated. The advantages of the molal scale are noted, and suggestion made that the ‘mokal’ scale be used only when there is insufficient information to convert oceanographic data to the molal scale.
Concentration Units and Comparison of Concentration Units
I. Concentration Units Quantitative study of a solution requires knowing its concentration, the amount of solute present in a given amount of solution. Chemists use different types of concentration units, each having its own advantages and limitations. 1. Types of Concentration Units (a) Percent by Mass (i) Formula: percent by mass = í µí±í µí±í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí± í µí± í µí±í µí±í µí± í µí± x 100% (ii) Unit: unitless, because it is a ratio of two similar (iii)Problem: A sample of 0.892 g of potassium chloride (KCl) is dissolved in 54.6 g of water. What is the percent by mass of KCl in the solution? (iv) Solution: percent by mass = 0.892 í µí±í µí± í µí°¾í µí°¾í µí°¾í µí°¾í µí±í µí± (0.892 í µí±í µí± í µí°¾í µí°¾í µí°¾í µí°¾í µí±í µí±+54.6 í µí±í µí± í µí°»í µí°»2í µí±í µí±) x 100 percent by mass = 1.61 % (b) Percent by Volume (i) Formula: percent by volume = í µí±í µí±í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±£í µí±£í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí± í µí± í µí±í µí±í µí± í µí± x 100% (ii) Unit: unitless (iii)Problem: In a solution, there is 111.0 mL (110.605 g) of solvent and 5.24 mL (6.0508 g) of solute. Find its percent by volume. (iv) Solution: percent by volume = 5.24 í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± (111.0 í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±£í µí±£í µí±í µí±í µí± í µí± í µí±í µí± +5.24 í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí±) x 100% percent by volume = 0.0450791466 x 100% percent by volume = 4.51% (c) Mass/Volume Percent (i) Formula: percent by volume = í µí±í µí±í µí±í µí±í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±£í µí±£í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí± í µí± í µí±í µí±í µí± í µí± x 100% (ii) Unit: unitless (iii)Problem: In a solution, there is 111.0 mL (110.605 g) of solvent and 5.24 mL (6.0508 g) of solute. Find its percent by mass/volume percentage. (iv) Solution: percent by volume = 6.0508 í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± (111.0 í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±£í µí±£í µí±í µí±í µí± í µí± í µí±í µí± +5.24 í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí± í µí±í µí±í µí±í µí±í µí±í µí±) x 100% percent by volume = 0.0520 x 100% percent by volume = 5.205%
Saturation units for use in aquatic bioassays
Chemosphere, 1999
Methods were developed for preparing liquid/liquid and glass wool column saturators for generating chemical stock solutions for conducting aquatic bioassays. Exposures have been conducted using several species offish, invertebrate, and mollusks in static and flow-through conditions using these methods. Stock solutions for 82 organic chemicals were prepared using these saturation units. The primary purpose of stock generation was to provide a continuous and consistent amount of toxicant laden solution at a measured analytical level which would be available to test organisms for the test duration. In the present study, the glass wool column and liquid/liquid saturators were used to provide consistent stock concentrations, at times approaching saturation, for fathead minnow (Pimephalespromelas) acute exposures. Attempts were made to achieve the maximum solubility of these compounds for comparison purposes to water solubility values available in the literature. Literature solubility values from a database by Yalkowsky et al. [1] provided information on temperatures and data quality which allowed comparison to values obtained from the present study. Twenty four compounds were identified and analyzed for the comparison of maximum obtainable solubility levels. Maximum saturator stock water concentrations were generally lower (R=0.98) but were in close agreement with published water solubility values.
Dilution and Concentration of Pharmaceutical Solutions and Other Physical Mixtures
Pharmaceutical Calculations, 2019
This chapter is essentially divided in two parts, that is, dilutions in drug compounding and dilutions in drug analysis, which are more useful to individuals engaged in research projects and laboratory work. The concept of dilution is first explained using a mass balance equation that was generated based on the fact that the mass of a substance is preserved during dilution processes implicated in compounded drug preparations. This same equation is then used to calculate the concentration of drugs in pharmaceutical products prepared by diluting a known amount of drug with other excipients or to calculate concentration of drugs in patient’s dose. The concept of the dilution factor is introduced to cope with problems that deal with the construction of calibration curves for quantitative drug analysis in dosage forms and biological fluids. In the second part of the chapter, it is made clear that dilution is usually made by reducing the mass of the drug present in the original stock solu...
MODULE 1 VOLUMETRIC METHODS: NEUTRALIZATION METHOD - PART 1
Objectives: At the end of this course, the learner is expected to: 1. define relevant terms in volumetric method of analysis 2. identify ways of expressing solution concentration 3. solve problems on direct acid-base (neutralization) titrations. VOLUMETRIC METHOD OF ANALYSIS Volumetric (Titrimetric) methods of analysis are analytical methods in which the volume of a solution of known concentration consumed during analysis is a measure of the amount of active constituent in a sample being analyzed. The chemical substance being analyzed is referred to as the analyte or the active constituent in the sample. A standard solution (titrant) is one whose concentration is accurately known. The process by which a standard solution is brought into reaction until the desired reaction is accomplished is known as titration. The indicator is usually a chemical which changes color at or very near the endpoint. Endpoint (practical) of a titration is shown by the change of color of the indicator. The theoretical point at which equivalent amounts of each substance have reacted is the equivalence point or stoichiometric point or theoretical endpoint. The theoretical and practical endpoints should coincide, otherwise the indicator used is not suitable to accomplish the endpoint of the titration. The following are the common methods of expressing concentration of standard solution used in
Microorganisms are often counted in the laboratory using such methods as the viable plate count where a dilution of a sample is plated onto (or into) an agar medium. After incubation, plates with 30-300 colonies per standard-sized plate are counted. This number of colonies (30-300) was chosen because the number counted is high enough to have statistical accuracy, yet low enough to avoid nutrient competition among the developing colonies. Each of the colonies is presumed to have arisen from only one cell, although this may not be true if pairs, chains, or groups of cells are not completely broken apart before plating. It is possible, but unlikely, for an original (undiluted) sample of microorganisms which is to be counted to have 30-300 cells/ml so that a pour plate using a 1 ml volume from the sample will give good results. More likely, a sample will have greater numbers of cells/ml; sometimes, as in the case of unpolluted water samples, the sample will have less. In either case, the sample must be manipulated so that it contains a number of cells in the correct range for plating. If the cell number is high, the sample is diluted; if too low, the sample is concentrated. Dilutions are performed by careful, aseptic pipetting of a known volume of sample into a known volume of a sterile buffer, water, or saline . This is mixed well and can be used for plating and/or further dilutions. If the number of cells/ml is unknown, then a range of dilutions are usually prepared and plated.
Environmental Toxicology and Chemistry, 2001
Most of the thousands of substances and species that risk assessment has to deal with are not investigated empirically because of financial, practical, and ethical constraints. To facilitate extrapolation, we have developed a model for concentration kinetics of inorganic substances as a function of the exposure concentration of the chemical and the weight and trophic level of the species. The ecological parameters and the resistances that substances encounter during diffusion in water layers were obtained from previous reviews. The other chemical parameters (the resistances for permeation of lipid layers) were calibrated in the present study on 1,062 rate constants for absorption from water, for assimilation from food, and for elimination. Data on all elements and species were collected, but most applied to aquatic species, in particular mollusks and fish, and to transition metals, in particular group IIB (Zn, Cd, Hg). Their ratio was validated on 92 regressions and nine geometric averages, representing thousands of (near-)equilibrium accumulation ratios from laboratory and field studies. Rate constants for absorption and elimination decreased with species weight at an exponent of about Ϫ0.25, known from ecological allometry. On average, uptake-rate constants decreased with about the reciprocal square root of the exposure concentration. About 71 and 30% of the variation in absorption and elimination was explained by the model, respectively. The efficiency for assimilation of elements from food appeared to be determined mainly by the food digestibility and the distribution over egested and digested fractions. (Near-)equilibrium accumulation and magnification ratios also decreased with the reciprocal square root of the exposure concentration. The level of the organism-solids concentrations ratios roughly varied between one and two orders of magnitude, depending on the number of elements and species groups investigated. Metal concentrations did not increase at higher trophic levels, with the exception of (methyl-)mercury. Organism-solids concentration ratios for terrestrial species tended to be somewhat lower than those for their aquatic equivalents. Food web accumulation, expressed as organism-organic solids and organism-food concentrations ratios, can therefore be only partly explained by ecological variables. The model is believed to facilitate various types of scientific interpretation as well as environmental risk assessment. ). in water, food, and biomass flows and on food digestibilities . The chemical parameters (the resistances for diffusion through water and permeation through membranes) were obtained in the present and in a related study by fitting rate constants on rate constants collected in a literature review . To validate the estimations, the quotient of the rate constants for influx and efflux were compared to equilibrium accumulation ratios from laboratory and field studies. A similar approach for organic xenobiotics was described in another paper . The two studies support extrapolation of information on well-known substances, species, and conditions to those that are less well investigated.
Ground water quality criteria" means the designated levels or concentrations of constituents that, when exceeded, will prohibit or significantly impair a designated use of water. Groundwater quality comprises the physical, chemical, and biological qualities of ground water. Temperature, turbidity, color, taste, and odor make up the list of physical water quality parameters.
Clarifying Misconceptions about Mass and Concentration Sensitivity
This commentary discusses differences between the so-called " mass sensitivity " and " concentration sensitivity ". These terms are freely used in analytical chemistry literature to characterize operation of analytical techniques and methods. The type of sensitivity in an analytical method delimits the method's applications (e.g., in analysis of volume-limited and concentrated, or large-volume but dilute samples). It is helpful to instruct students how to distinguish between mass-sensitive and concentration-sensitive methods. Introduction of mass and concentration sensitivity can be included in graduate courses related to instrumental analysis, and, if time is available, also in the upper-level undergraduate courses.