Analysis volumetric

Major Analytical Techniques Based on Color Volumetric Analysis Chromatography Spectroscopy Color Measurement 

Robert Wilhelm Bunsen (1811-1899) had introduced iodometric methods of analysis [5]. 

Titrations that use the human eye as the primary detector are based on color change. Other types of titrations that rely on color change are oxidation-reduction, precipitation, and complexometric titrations. Other detectors indicate voltage or other types of changes such as potentiometric titrations, conductometric titrations and amperometric titrations—all of which require additional instrumentation—and may be quite colorless. 

The procedure involved in finding the concentration of a solution is called volumetric analysis. It involves reacting a solution of known concentration (a standard solution) with one of unknown concentration, in order to determine the equivalence point. 

The equivalence point is reached when the reactants have reacted together in an exact ratio of quantities, as given in the balanced equation for the reaction. For example, in an acid-base titration, the equivalence point involves addition of exactly enough base to neutralize any acid present. 

The technique whereby one reactant is slowly added to a second reagent until the equivalence point is reached is called a titration. Chemicai indicators are substances that change colour at a particular ratio of reactant concentrations called the endpoint. In a titration, a chemical indicator is chosen so that the endpoint and equivalence point are the same. 

By measuring the volumes of the solutions that have reacted together, and using the balanced equation for the reaction, the unknown solution concentration can be determined. If carried out carefully, volumetric analysis is quite an accurate technique and a skilled worker should determine an unknown concentration within an error of no more than 0.2%. 

The (previously unknown) concentration of an acid can be determined by titrating it with a standard alkaline solution. The acid is neutralized by the alkali. The procedure is as follows  

As you saw earlier, you can use molarity as a conversion factor, and in this way you can calculate the volume of solution that is equivalent to a given mass of solute (see Example 4.10). This means that you can replace mass measurements in solution reactions by volume measurements. In the next example, we look at the volumes of solutions involved in a given reaction. 

EXAMPLE 4.13 ] Calculating the Volume of Reactant Solution Needed 

Consider the reaction of sulfuric acid, H2SO4, with sodium hydroxide, NaOH. 

Suppose a beaker contains 35.0 mL of 0.175 Af H2SO4. How many milliliters of 0.250 M NaOH must be added to react completely with the sulfuric acid  

You convert from 35.0 mL (or 35.0 X 10 L) H2SO4 solution to moles H2SO4 (using the molarity of H2SO4), then to moles NaOH (from the chemical equation). Finally, you convert this to volume of NaOH solution (using the molarity of NaOH). 

In this procedure a substance dissolved in the water is reacted with a titrant of known concentration. The end point of the reaction is indicated either by an indicator changing colour, by a precipitate forming or 

volumetric determination of dissolved substances in water can be automated. With appropriate equipment, it is possible not only to direct the reaction quantitatively, but also to evaluate the endpoint of the reaction electrometrically and print it out, for example, or produce a titration diagram. The experience of the authors has shown the volumetric procedures described in Chapters 3 and 4 to be of particular value in practical water analysis in the laboratory. 

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The problem in any quantitative volumetric analysis for ions in solution is to determine accurately the equivalence point. This is often found by using an indicator, but in redox reactions it can often... 

Sodium thiosulphate is an important reducing agent used in volumetric analysis for the estimation of iodine ... 

The ability of the solid chlorates(V) to provide oxygen led to their use in matches and fireworks. Bromates(V) and iodates(V) are used in quantitative volumetric analysis. Potassium hydrogen diiodate(V), KHflOjlj, is used to standardise solutions of sodium thiosulphate(Vf) since in the presence of excess potassium iodide and acid, the reaction... 

The dichromate ion is a useful oxidising agent in acid solution, and is used in volumetric analysis ... 

The information given in this table is from the two-volume work Volumetric Analysis by Kolthoff and Stenger, published by Interscience Publishers, Inc., New York, 1942 and 1947, and reproduced with their permission. 

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

The most popular device for fluoride analysis is the ion-selective electrode (see Electro analytical techniques). Analysis usiag the electrode is rapid and this is especially useful for dilute solutions and water analysis. Because the electrode responds only to free fluoride ion, care must be taken to convert complexed fluoride ions to free fluoride to obtain the total fluoride value (8). The fluoride electrode also can be used as an end poiat detector ia titration of fluoride usiag lanthanum nitrate [10099-59-9]. Often volumetric analysis by titration with thorium nitrate [13823-29-5] or lanthanum nitrate is the method of choice. The fluoride is preferably steam distilled from perchloric or sulfuric acid to prevent iaterference (9,10). Fusion with a sodium carbonate—sodium hydroxide mixture or sodium maybe required if the samples are covalent or iasoluble. 

See Temperature MEASUREMENT Therptal, gravimetric, and volumetric analysis. 

Arsenic trioxide may be made by burning arsenic in air or by the hydrolysis of an arsenic trihaUde. Commercially, it is obtained by roasting arsenopyrite [1303-18-0] FeAsS. It dissolves in water to a slight extent (1.7 g/100 g water at 25°C) to form a weaMy acidic solution which probably contains the species H AsO, orthoarsenous acid [36465-76-6]. The oxide is amphoteric and hence soluble in acids and bases. It is frequendy used as a primary analytical standard in oxidimetry because it is readily attainable in a high state of purity and is quantitatively oxidized by many reagents commonly used in volumetric analysis, eg, dichromate, nitric acid, hypochlorite, and inon(III). 

Potassium biiodate [13455-24-8] M 389.9. Crystd three times from hot water (3mL/g), stirred continuously during each cooling. After drying at 100° for several hours, the crystals are suitable for use in volumetric analysis. 

Potassium hydrogen phthalate [877-24-7] M 204.2. Crystd first from a dilute aqueous solution of K2CO3, then H20(3mL/g) between 100° and 0°. Before being used as a standard in volumetric analysis, analytical grade potassium hydrogen phthalate should be dried at 120° for 2h, then allowed to cool in a desiccator. 

Constituent Symbol Molecular weight (M) Volumetric analysis % Gravimetric analysis %... 

Gravimetric analysis The chemical analysis of materials by the separation of the constituents and their measurement by weight. This describes the gas mixture by giving the percentage by weight of each component gas. See also Volumetric analysis. 

Volumetric analysis The determination of the amount of a particular gas in a mixture of gases, as the percentage of the total volume. See Gravimetric analysis. 

Thus the quantitative oxidation of 8203 " by I2 to form tetrathionate and iodide is the basis for the iodometric titrations in volumetric analysis... 

This last reaction finds use in volumetric analysis. The use of sulfamic acid to stabilize chlorinated water depends on the equilibrium formation of A-chlorosulfamic acid, which reduces loss of chlorine by evaporation, and slowly re-releases hypochlorous acid by the reverse hydrolysis ... 

In addition to its uses in photography and medicine, iodine and its compounds have been much exploited in volumetric analysis (iodometry and iodimetry, p. 864). Organoiodine compounds have also played a notable part in the development of synthetic organic chemistry, being the first compounds used in A. W. von Hofmann s alkylation of amines (1850), A. W. Williamson s synthesis of ethers (1851), A. Wurtz s coupling reactions (1855) and V. Grignard s reagents (1900). 

An important series of reactions, which illustrates the diversity of behaviour to be expected, is the comproportionation of halates and halides. Bromides are oxidized quantitatively to bromine and iodides to iodine, this latter reaction being much used in volumetric analysis ... 

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