Question

Discuss how you would carry out the following analyses: (a) calcium levels in breakfast cereal, (b) mercury in shellfish (c) the geometry of BrF5, (d)number of organic ligands in a d-metal complex, (e) water of crystallization in an inorganic salt.

Answer 1

eactivos

Hydrochloric acid (1-3%)
Nitric acid 70%
Ammonium hydroxide (1: 1 v / v)
Methyl red indicator (1 g in 200 ml of ethanol)
Ammonium oxalate solution 4.2%
Sulphuric acid 98%
standard potassium permanganate solution 0.05N
Materials and Equipment

porcelain crucibles
250 ml volumetric flasks
Beakers 250 ml
free filter paper for quantitative analysis of ash
Process

Calcine in porcelain crucible 2.5g of finely ground sample. Adicione 40ml of HCI and a few drops of HNO3 to the residue, heat the pot to boiling, cool and transfer to a 250ml volumetric flask, Afore and mix. Transfer to a 100 ml beaker sun. cereal or cereal foods or foods with 25ml for minerals. Dilute to 100 ml and add 2 drops of methyl red. Adicione NH4OH dropwise until the color turns orange-brown, then add 2 drops of HCl to give a pink color. Dilute with 50 ml of water, boil and add with stirring 10 ml of 4.2% sun ammonium oxalate. Adjust the pH with acid to return to pink if necessary.

Let stand, filter and wash the precipitate with the NH4OH solution (1.5%). Place the filter paper and precipitate in a glass, add a mixture of 125 ml of water and 5 ml of H2SO4, heated to 70 ° C and titrate with permanganate solution and calculate:

Ca (%) = 0.1 ((ml Sol. Permanganato / sample weight) × (Aliquot used in ml / 250)

Hg

1kg of fish tissue homogenate, which was divided into 7 portions of 100 g each. One of these portions was contaminated with a pattern methylmercury (Sigma Chemical Co.) at a level of 1 mg / kg for repeatability study. Another portion remained uncontaminated target sample, to know the matrix interferences. The remaining portions were contaminated with 0.2; 0.5; 1; 5 and 10 m g / kg respectively for recovery studies. Each portion was contaminated subdivided into test samples of 5 g each. The test samples were processed by the technique described by the Association of Official Analytical Chemists (AOAC) International, for purification and extraction of methylmercury.

In the identification and quantification of methylmercury 5m L of the extract was injected into a column 2 m long and 2 mm internal diameter packed with 5% DEGS-PS on Supelcoport 100-120 mesh, with the following chromatographic conditions: temperature detector 300 ° C, injector temperature 200 ° C, column temperature 155 ° C, carrier gas flow 30 mL / min, purge detector 100 mL / min and the bias current in 8. Under these conditions compared the response of the test sample contaminated with patterns and concentration of methylmercury by the following equation is calculated:

geometry

The molecular geometries are best determined when the samples are close to absolute zero because at higher temperatures the molecules present a substantial rotational movement. In the solid state molecular geometry can be measured by X-ray diffraction geometries can be calculated by quantum mechanical procedures or semiempirical ab initio molecular modeling methods.

The position of each atom is determined by the nature of the chemical bonds with which it is connected to its neighboring atoms. The molecular geometry can be described by the positions of these atoms in space, mentioning the bond length of two atoms bonded, bond angle and three atoms connected torsion angle of three consecutive links.

X-rays are diffracted by electrons around atoms being the wavelength of the same order of magnitude as the atomic radius. The beam of X-rays emerging after this interaction contains information on the position and type of atoms found in their way. Crystals, thanks to its periodic structure, the elastically scattered X-ray beams in certain directions and amplified by constructive interference, causing a pattern difracción.n. 1 There are several types of special detectors to observe and measure the intensity and position of the diffracted X-rays, and subsequent analysis by mathematical means allows a representation at the atomic scale of atoms and molecules of the material studied.

There are several ways to determine the number of coordinated ligands in a complex ranging from gravimetric weight of the compounds source metal and organic groups known and weight of compounds known produced as metal determining reaction to form the complex we have the number of moles of metal as we know that the moles formed complex are equal to the moles that reacted to form the complex thus knowing the number of moles of the complex and determining how many moles are we not react the organic substance the subtraction gives us the number of moles that are present in the complex stoichiometry then determined by the number of ligands present in that compound

another way is by spectrometry as by absorvacia against a wavelength of a compound is known and this varies depending on the number of ligands present as both its length adsorvancia which absorbs

water of cristalizacion

The most general method for determining the water of hydration of the salt is
separating said hydration water by evaporation, by applying
hot. The amount of evaporated water is determined by the weight loss of the sample.
For that,
1. a porcelain crucible, to which was added 4 or 5 grams of substance is weighed, and
it is reweighed.
2. the vessel is heated direct flame, but slowly, to avoid
projections solid or water vapor.
3. vapor release is observed.
4. Remove any traces of water in the container walls with paper
filter. Reweighing the container and record the result.
5. Reheat the container, and despite again after waiting to cool.
Check that the weight has remained constant.
6. The percentage of water of hydration can be calculated with the following formula


Where mo = mass of the initial salt final mass = mf