Sampling of water

Information is given below on carrying out the local inspection and the 

The key points summarized below for water sampling are to be seen as 

The following key points supplement each other and also partly overlap, so that if they are followed information can be gathered on different aspects. 

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The environmental sampling of waters and wastewaters provides a good illustration of many of the methods used to sample solutions. The chemical composition of surface waters, such as streams, rivers, lakes, estuaries, and oceans, is influenced by flow rate and depth. Rapidly flowing shallow streams and rivers, and shallow (<5 m) lakes are usually well mixed and show little stratification with... 

A 200.0-mL sample of water was filtered through a preweighed glass fiber filter. After drying to constant weight at 105 °C, the filter was found to have increased in mass by 48.2 mg. Determine the total suspended solids for the sample in parts per million. 

The concentration of Ch in a 100.0-mL sample of water drawn from a fresh water acquifer suffering from encroachment of sea water, was determined by titrating with 0.0516 M Hg(N03)2. The sample was acidified and titrated to the diphenylcarbazone end point, requiring 6.18 mb of the titrant. Report the concentration of Cb in parts per million. 

One standard method for determining the dissolved O2 content of natural waters and wastewaters is the Winkler method. A sample of water is collected in a fashion that prevents its exposure to the atmosphere (which might change the level of dissolved O2). The sample is then treated with a solution of MnS04, and then with a solution of NaOH and KI. Under these alkaline conditions Mn + is oxidized to Mn02 by the dissolved oxygen. 

Explain why it is not possible for a sample of water to simultaneously have OH and HC03 as sources of alkalinity. 

What is the concentration of As(III) in a sample of water if the peak current under the same conditions is 1.37 )J,A ... 

A 50.00-mL sample of water is placed in a coulometric cell, along with an excess of KI and a small amount of starch as an indicator. Electrolysis is carried out at a constant current of 84.6 mA, requiring 386 s to reach the starch end point. Report the concentration of H2S in the sample in parts per million. 

Analysis of water from a drinking fountain gives areas of f.56 X i0 5.f3 X i0 f.49 X fOk and f.76 X fO- for GHGI3, GHGl2Br, GHGlBr2, and GHBr3, respectively. Determine the concentration of each of the trihalomethanes in the sample of water. 

A solution s ionic balance is defined as the ratio of the total cation charge to the total anion charge. Determine the ion balance for this sample of water, and comment on whether the result is reasonable. 

The analysis of N03 in aquarium water was carried out by CZE using 104 as an internal standard. A standard solution of 15.0-ppm N03 and 10.0-ppm 104 gives peak heights (arbitrary units) of 95.0 and 100.1, respectively. A sample of water from an aquarium is diluted 1 100, and sufficient internal standard added to make its concentration 10.0 ppm. Analysis gives signals of 29.2 and 105.8 for N03 and 104 , respectively. Report the parts per million of N03 in the sample of aquarium water. 

Acidity. Acidity is the base-neutrali2ing capacity of a sample of water. It is determined by titration of the sample with standard base to pH 8.3... 

The difference between the actual pH (pH of a sample of water and the pH called the LangeHer saturation index. This index is a... 

Figure 20-9 shows the negative effect of uninsulated heating elements on corrosion protection. In a 250-liter tank, an electric tube heating element with a 0.05-m surface area was screwed into the upper third without electrical separation, and in the lower third a tinned copper tube heat exchanger with a 0.61 -m surface area was built in. The Cu heat exchanger was short-circuited for measurements, as required. For cathodic protection, a potential-controlled protection system with impressed current anodes was installed between the two heating elements. The measurements were carried out with two different samples of water with different conductivities. 

The percent composition of a compound is specified by citing the mass percents of the elements present. For example, in a 100-g sample of water there are 11.19 g of hydrogen and 88.81 g of oxygen. Hence the percentages of the two elements are... 

This is a common-sense rule, consistent with experience. The amount of heat that must be absorbed to boil a sample of water is directly proportional to its mass. In another case, the more gasoline you bum in your cars engine, the more energy you produce. 

The amount of oxygen dissolved in a sample of water can be determined by using thallium metal containing a small amount of the isotope Tl-204. When excess thallium is added to oxygen-containing water, the following reaction occurs. 

A 100.0-g sample of water containing tritium, H, emits 2.89 X 103 beta particles per second. Tritium has a half-life of 123 years. What percentage of all the hydrogen atoms in the water sample is tritium ... 

In Experiment 5, the weight of a sample of water is determined by subtracting the weight of the empty can from the weight of the can containing the water. 

In a similar way, if we boil a sample of water until half of it has changed to steam, condense the steam to water in a different vessel, and then compare the separate samples, we find that the fractions of the original sample are indistinguishable. Such behavior on boiling (condensing) or freezing (melting) characterizes pure substances. Solutions behave differently. 

Commercial samples of water are frequently alkaline due to the presence of hydrogencarbonates, carbonates, or hydroxides. The alkalinity is determined by titrating a 100.0 mL sample with 0.02M hydrochloric acid using screened methyl orange as indicator (or to a pH of 3.8). To obtain the total cation content in terms of CaC03, the total methyl orange alkalinity is added to the EMA. 

Procedure. To a 50 mL sample of the water to be tested add 1 mL buffer solution (ammonium hydroxide/ammonium chloride, pH 10, Section 10.54) and 30-40 mg solochrome black indicator mixture. Titrate with standard EDTA solution (0.01 M) until the colour changes from red to pure blue. Should there be no magnesium present in the sample of water it is necessary to add 0.1 mL magnesium-EDTA solution (0.1 M) before adding the indicator (see Section 10.54). The total hardness is expressed in parts of CaC03 per million of water. 

Notes. (1) Somewhat sharper end points may be obtained if the sample of water is first acidified with dilute hydrochloric acid, boiled for about a minute to drive off carbon dioxide, cooled, neutralised with sodium hydroxide solution, buffer and indicator solution added, and then titrated with EDTA as above. 

The permanent hardness of a sample of water may be determined as follows. Place 250 mL of the sample of water in a 600 mL beaker and boil gently for 20-30 minutes. Cool and filter it directly into a 250mL graduated flask do not wash the filter paper,... 

If it is desired to determine both the calcium and the magnesium in a sample of water, determine first the total calcium and magnesium content as above, and calculate the result as parts per million of CaC03. 

Discussion. One of the most useful titrations involving iodine is that originally developed by Winkler18 to determine the amount of oxygen in samples of water. The dissolved oxygen content is not only important with respect to the species of aquatic life which can survive in the water, but is also a measure of its ability to oxidise organic impurities in the water (see also Section 10.103). Despite the advent of the oxygen-selective electrode (Section 16.36) direct titrations on water samples are still used extensively.19... 

A venturi meter with a 50 mm throat is used to measure a flow of slightly salty water in a pipe of inside diameter 100 mm. The meter is checked by adding 20 cm3/s of normal sodium chloride solution above the meter and analysing a sample of water downstream from the meter. Before addition of the salt, 1000 cm- of water requires 10 cm3 of 0.1 M silver nitrate solution in a titration. 1000 cm3 of the downstream sample required 23.5 cm3 of 0.1 M silver nitrate. If a mercury-under-water manometer connected to the meter gives a reading of 20S mm, what is the discharge coefficient of the meter Assume that the density of the liquid is not appreciably affected by the salt. 

Chemistry is concerned with the properties of matter, its distinguishing characteristics. A physical property of a substance is a characteristic that we can observe or measure without changing the identity of the substance. For example, a physical property of a sample of water is its mass another is its temperature. Physical properties include characteristics such as melting point (the temperature at which a solid turns into a liquid), hardness, color, state of matter (solid, liquid, or gas), and density. A chemical property refers to the ability of a substance to change into another substance. For example, a chemical property of the gas hydrogen is that it reacts with (burns in) oxygen to produce water a chemical property of the metal zinc is that it reacts with acids to produce hydrogen gas. The rest of the book is concerned primarily with chemical properties here we shall review some important physical properties. 

Precipitation reactions have many applications. One is to make compounds. The strategy is to choose starting solutions that form a precipitate of the desired insoluble compound when they are mixed. Then we can separate the insoluble compound from the reaction mixture by filtration. Another application is in chemical analysis. In qualitative analysis—the determination of the substances present in a sample—the formation of a precipitate is used to confirm the identity of certain ions. In quantitative analysis, the aim is to determine the amount of each substance or element present. In particular, in gravimetric analysis, the amount of substance present is determined by measurements of mass. In this application, an insoluble compound is precipitated, the precipitate is filtered off and weighed, and from its mass the amount of a substance in one of the original solutions is calculated (Fig. 1.6). Gravimetric analysis can be used in environmental monitoring to find out how much of a heavy metal ion, such as lead or mercury, is in a sample of water. 

He placed two 150.-g samples of water at 0.00°C (one ice and one liquid) in a room kept at a constant temperature of 5.00°C. He then observed how long it took for each sample to warm to its final temperature. The liquid sample reached 5.00°C after 30.0 min. However, the ice took 10.5 h to reach 5.00°C. He concluded that the difference in time that the two samples required to reach the same final temperature represented the difference in heat required to raise the temperatures of the samples. Use Black s data to calculate the enthalpy of fusion of ice in kj-mol-1. Use the known heat capacity of liquid water. 

The carbon dioxide gas dissolved in a sample of water in a partly filled, sealed container has reached equilibrium with its partial pressure in the air above the solution. Explain what happens to the solubility of the CO, if (a) the partial pressure of the CO, gas is doubled by the addition of more CO, (b) the total pressure of the gas above the liquid is doubled by the addition of nitrogen. 

The two most common isotopes of oxygen are and 0, and the two natural isotopes of hydrogen are and or D (deuterium). If a sample of carbonate contains Cis moles of and Ci6 moles of then define the heavy light ratio as Ris = Cia/Cie- Similarly, natural water molecules are mostly of three types H O, H] 0, and HD O. For a given sample of water, call the number of moles of each W, W g, and Wq, respectively. Then define the heavyriight ratios as ki8 = Wig/VV and Rp = WqIW. For either water or carbonate, the 5 are defined as deviations of these ratios from standard values for these ratios (call the ratios of the standards Sig and Sq) ... 

An appropriate mineral medium supplemented with the organic compound that is to be studied is inoculated with a sample of water, soil, or sediment. In studies of the environmental fate of a xenobiotic in a specific ecosystem, samples are generally taken from the area putatively contaminated with the given compound so that a degree of environmental relevance is automatically incorporated. Attention has, in addition been directed to pristine environments, and the issues of adaptation or preexposure have already been discussed. 

Comprehensive chemical analyses of samples of water, sediment, and biota were carried out both before and after the spill. This cannot of course be carried out in most cases, and illustrates a serious limitation in field studies, in which lack of background data or difficulty in finding an uncontaminated control locality is frequently encountered. Sum parameters were sparingly employed in Baffin Island Oil Spill (BIOS), and emphasis was placed on the analysis of specific compounds attention was directed not only to PAHs, but also to azaarenes, dibenzothiophenes, and hopanes. Thereby, a clear distinction could be made between the input from the oil deliberately discharged, and that arising from natural biological reactions or mediated by atmospheric transport. 

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