Gravimetric factor examples

This can be done with the use of a gravimetric factor. Examples include the sulfate and iron determinations in the experiments at the end of this chapter (see Experiments 6 and 7). 

The weight of the precipitate after filtering and drying can then be measured free of any influence from the NaCl and converted back to the weight of the analyte with the use of a gravimetric factor (see the next section) and its percent in the sample calculated. Examples are given in Section 3.6.4. 

A gravimetric factor is a number used to convert, by multiplication, the weight of one chemical to the weight of another. Such a conversion can be very useful in an analytical laboratory. For example, if a recipe for a solution of iron calls for 55 g of FeCl3 but a technician finds only iron wire on the chemical shelf, he or she would want to know how much iron metal is equivalent to 55 g of FeCl3 so that he or she could prepare the solution with the iron wire instead and have the same weight of iron in either case. In one formula unit of FeCl3, there is one atom of Fe, so the fraction of iron(III) chloride that is iron metal is calculated as follows ... 

As stated earlier, gravimetric factors are used to convert the weight of one chemical to the weight of another, as in the example cited at the beginning of Section 3.6.3. Below is another example of such a conversion. 

The term gravimetric factor is generally employed which represents the number of grams of the desired constituent in 1 g of the substance weighed. It can be further expatiated with the help of the following examples ... 

For a reaction in which the stoichiometric relation between analyte and product is not 1 1, we must use the correct stoichiometry in formulating the gravimetric factor. For example, an unknown containing Mg2+ (atomic mass = 24.305 0) can be analyzed gravimetrically to produce magnesium pyrophosphate (Mg2P207. FM 222.553). The gravimetric factor would be... 

Following are some other examples of gravimetric factors ... 

Using the atomic mass spread sheets described in Example 1.2, calculate and record suitably on the spreadsheet the gravimetric factors for the following ... 

These two exercises introduce the notion of gravimetric factor or analytical factor. It is defined as the ratio of the analyte mass and the mass of the compound that is weighed. In the first example, the analytical factor was 1 [M(Cl)/M(AgCl)], and in... 

The principle of solubility product is the major factor in governing the gravimetric analysis. Justify the statement adequately with appropriate examples. 

In this expression, bd and bc refer to the appropriate anodic and cathodic Tafel constants. Comparison of weight loss data collected as a function of exposure time determined from R , Rf from EIS, and gravimetric measurements of mild steel exposure to 0.5 M H2S04 are often within a factor of two. This suggests that use of Rn in the Stern-Geary equation may be appropriate for the estimation of corrosion rate (147-150). However, Rn measurements may underestimate corrosion rates. / p is often measured at effective frequencies of 1(T2 Hz or less in linear polarization or EIS measurements, while Rn is measured at 1 Hz or greater. An example of this is provided in Fig. 57, which shows the corrosion rate of carbon steel in 3% NaCl solution as a function of exposure time determined by EIS, linear polarization, noise resistance, and direct current measurement with a ZRA. Among these data, the corrosion rates determined by noise resistance are consistently the lowest. 

Isolated examples of studies of the decomposition of other nitrocompounds of specialized interest include the thermal decomposition of thin films of nitrocellulose examined by infrared spectroscopy and by a gravimetric technique s . The kinetics are best approximated by a first order curve with two or three branches. Typical values of the activation energy and Arrhenius pre-exponential factor are 45.0 kcal.mole S and 3.54 x 10 sec". ... 

Here s is a numerical shape factor being s = 1/3 for simple cubic crystals and freely rotating molecules [6.22, 6.24], For non-polar admolecules (p = 0) numerical values of a = aj gravimetric measurements (cp. examples given in Sect. 3.2). For polar admolecules the same is true at least at low frequencies (v < 1 MHz) of the electric field where often um tton and hence can be neglected compared to Oori- For both types of admolecules numerical data of (a) are between their values for the gas and the liquid phase of the adsorptive and normally depend on the amount adsorbed, i. e. degree of saturation. Hence they can give an indication of the nature of the site where the admolecule is adsorbed and also on the structure of the sorbate phase [6.3]. 

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