Formula unit conversions

The Excel spreadsheet is constructed so that on page one, the referenced properties are listed in Column C, and the same with conversion factors to SI units in Column D. Conversion formulas and values calculated in SI Units are in Column E. Column F is a duplicate of Column E, and this can be used for additional calculation by changing to other conditions or to an entirely new case. It is recommended toleave Column E alone for a comparison case and to copy Column F to another page to execute calculations. 

Ans. There are 6.02 X 10 i atoms in 1.00 mol Na (Avogadro s number). There is 23.0 g of Na in LOO mol Na (equal to the atomic weight in grams). This problem requires use of two of the most important conversion factors involving moles. Note which one is used with masses and which one is used with numbers of atoms (or molecules of formula units). With numbers of atoms, molecules, or formula units, use Avogadro s number with mass or weight use the formula weight. 

Fig. 8-5 Conversion of formula units of a reactant to formula units of a product...

Tables 3 and 4 contain values of the log water activity and log sulfuric acid activity in molarity units. These can be obtained at any temperature by using the polynomial coefficients supplied by Zeleznik,45 which are based on all of the preexisting thermodynamic data obtained for this medium. The numbers were converted to the molarity scale using the conversion formula given in Robinson and Stokes 46 Molarity-based water activities are given for HCIO4 in Tables 5 and 6. These are calculated from data obtained at 25°C by Pearce and Nelson,17...

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 ... 

Table 1. Conversion Formulas for Various Concentration Units... 

The Imaginary scale and the Celsius scale both have the same zero point (the freezing point of water), but they differ in the size of their units. The readings on the Celsius scale will always be just 100/180 = 5/9 of the readings on the Imaginary scale, so the conversion formula from one to the other is... 

The principles to be followed in dynamic abrasion resistance measurement and the presentation of results as mean Mackensen-Mohs hardness (/fMM) or H0 hardness classes, on the basis of conversion formulae were discussed in detail in Chapter 4, along with analysis of the theoretical validity of the method and its comparison with other hardness measuring techniques. However, we do not have to convert to hardness units in every practical measurement. Often, determination of the susceptibility of a material to erosive destruction should prove an adequate engineering characteristic of a material. 

We can use Avogadro s number as a conversion factor to convert moles to numbers of formula units, and vice versa. We can use the molar mass to convert moles to masses, and vice versa (Figure 7.1). 

The chemical formula for a compound gives the ratio of atoms of each element in the compound to atoms of every other element in the compound. It also gives the ratio of dozens of atoms of each element in the compound to dozens of atoms of every other element in the compound. Moreover, it gives the ratio of moles of atoms of each element in the compound to moles of atoms of every other element in the compound. For example, a given quantity of H2O has 2 mol of H atoms for every mole of O atoms, and a given quantity of CH4 has 1 mol of C atoms for every 4 mol of H atoms. The mole ratio from the formula can be used as a factor to convert from moles of any element in the formula to moles of any other element or to moles of the formula unit as a whole. In Figure 7.2, these additional conversions have been added to those already presented in Figure 7.1. 

The mole is defined as the number of atoms in exactly 12 g of which is 6.02 X 10 —Avogadro s number. Equal numbers of moles of two (or more) different substances have the same number of formula units but not the same mass. The molar mass is the mass in grams of one mole of a substance. The number of grams per mole—the molar mass— is a frequently used conversion factor, used for converting between grams and moles. (Section 7.3)... 

What conversion factor is used to convert a number of moles of a substance to (a) the number of grams of the substance (b) the number of formula units of the substance ... 

Since all concentration units in the airshed model are expressed as parts per million (ppm), the following conversion formula is used ... 

What conversion factor do you use in converting number of moles into number of formula units ... 

Example Problem 11-8 illustrated how to find the number of moles of a compound contained in a given mass. Now, you will learn how to calculate the number of representative particles—molecules or formula units—contained in a given mass and, in addition, the number of atoms or ions. Recall that no direct conversion is possible between mass and number of particles. You must first convert the given mass to moles by multiplying by the inverse of the molar mass. Then, you can convert moles to the number of representative particles by multiplying by Avogadro s number. To determine numbers of atoms or ions in a compound, you will need conversion factors that are ratios of the number of atoms or ions in the compound to one mole of compound. These are based on the chemical formula. Example Problem 11-9 provides practice in solving this type of problem. 

You are given 35.6 g AICI3 and must calculate the number of Al + ions, the number of Cl ions, and the mass in grams of one formula unit of AICI3. Molar mass, Avogadro s number, and ratios from the chemical formula are the necessary conversion factors. The ratio of AP+ ions to CE ions in the chemical formula Is 1 3. Therefore, the calculated numbers of ions should be in that ratio. The mass of one formula unit in grams should be an extremely small number. 

Calculate the mass in grams of one formula unit of AICI3. Start with molar mass and use the inverse of Avogadro s number as a conversion factor. 

You make unit conversions everyday when you determine how many quarters are needed to make a dollar or how many feet are in a yard. One unit that is often used in calculations in chemistry is the mole. Chapter 11 shows you equivalent relationships among mole, grams, and the number of representative particles (atoms, molecules, formula units, or ions). For example, one mole of a substance contains 6.02 X 10 representative particles. Try the next example to see how this information can be used in a conversion factor to determine the number of atoms in a sample of manganese. 

Step 3 Make mole formula unit conversion. 0.0778 j f Ag2Cr04 x 6.02 x 10 3 formula units... 

Step 3 Make mole formula unit conversion. 

Another item of the forthcoming recommendation by the WG127 concerns a new salinity definition called Reference-Composition Salinity, bringing this fundamental oceanographic measure back into the interdisciplinary scientific and engineering family of the SI system of units (BIPM, 2006 Millero et al., 2008). The chemical Reference Composition is given in Table 20.1. On the basis of this definition, the recommended conversion formula between Absolute Salinity, S, and Practical Sahnity, S, of standard seawater is given by... 

As we saw with mass and moles of elements and molecular compounds, it is important to be able to convert between mass and moles of ionic substances. The development of the tools for this conversion starts with the determination of the formula mass, which is the weighted average of the masses of the naturally occurring formula units of the substance. (It is analogous to the atomic mass for an element and the molecular mass for a molecular substance.)... 

The relationship between the molar mass of BaF2 and Avogadro s number of formula units provides the conversion factor needed to solve the problem. 

In a similar way, we use Avogadro s number, which expresses the equivalent relationship between 1 mole of a substance and the number of entities it contains, as a conversion factor. We multiply by Avogadro s number to convert amount of substance (in moles) to the number of entities (atoms, molecules, or formula units) ... 

A mole of substance is the amount that contains Avogadro s number (6.022x10 ) of chemical entities (atoms, molecules, or formula units). The mass (in grams) of a mole has the same numerical value as the mass (in amu) of the entity. Thus, the mole allows us to count entitles by weighing them. Using the molar mass (jM., g/mol) of an element (or compound) and Avogadro s number as conversion factors, we can convert among amount (mol), mass (g), and number of entities. The mass fraction of element X in a compound is used to find the mass of X in any amount of the compound. 

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