Compound formula mass

Ionic compounds, however, are composed of ions, not covalently bonded atoms. For ionic compounds formula mass should be used instead of molecular mass and empirical formula, simplest formula or formula unit should be used instead molecular formula. 

Compound Formula mass Ambient air concentrations Blood/urine concentrations ... 

In addition to giving a characteristic mass to the molecules or formula units of a compound, formula mass—as we will learn in Chapter 6—allows us to quantify the number of molecules or formula units in a sample of a given mass. 

The molar mass of a compound, the mass per mole of its molecules or formula units, is used to convert between the mass of a sample and the amount of molecules or formula units that it contains. 

Ans. The figure is presented as Fig. 4-4. One can convert from mass to moles, moles of component elements, or number of formula units. Additionally, one can convert from number of formula units to moles, to moles of component elements, or to mass. Also from moles of component elements to moles of compound, number of formula units of compound, or mass of compound. Finally, from moles of compound to number of formula units, mass, or number of moles of component elements. 

In the problem above, we determined the percentage data from the chemical formula. We can determine the empirical formula if we know the percent compositions of the various elements. The empirical formula tells us what elements are present in the compound and the simplest whole-number ratio of elements. The data may be in terms of percentage, or mass or even moles. However, the procedure is still the same—convert each element to moles, divide each by the smallest, and then use an appropriate multiplier if necessary. We can then determine the empirical formula mass. If we know the actual molecular mass, dividing the molecular formula mass by the empirical formula mass, gives an integer (rounded if needed) that we can multiply each of the subscripts in the empirical formula. This gives the molecular (actual) formula, which tells what elements are in the compound and the actual number of each. 

Use the formulas of methane, ethane, and propane to calculate the compounds molar masses. 

The mass spectrum shown is that for ethanol (CHjCHjOH). The 100-peak with the highest m/z ratio provides the gram formula mass of the organic compound. In the example, this appears at m/z = 46 and confirms the gram formula mass of ethanol as 46 g. 

Chemists may distinguish between the molar masses of pure elements, molecular compounds, and ionic compounds by referring to them as the gram atomic mass, gram molecular mass, and gram formula mass, respectively. Don t be fooled The basic concept behind each term is the same molar mass. 

To determine a moleculcir formula, you must know the gram formula mass of the compound as well as the empirical formula (or enough information to calculate it yourself from the percent composition see the preceding section for details). With these tools in hand, calculating the molecular formula involves three steps ... 

What is the molecular formula of a compound that has a gram formula mass of 78 g/mol and the empirical formula NaO ... 

Na202. First, find the empirical formula mass of NaO, which is 38.99 g/mol. You determine this by adding one Na (22.99) to one O (16.00). Then divide the grcim formula mass of the mystery compound, 78 g/mol, by this empirical formula mass to obtain the quotient, 2. Multiply each of the subscripts within the empirical formula by this number to obtain Na202. You ve just found the molecular formula for sodium peroxide. 

The empirical formula mass is 97.1 g/mol, which you calculate by multiplying the number of atoms of each element in the compound by the element s atomic mass and adding them all up ... 

Dividing the gram molecular mass you were given (194.2 g/mol) by this empirical formula mass yields the quotient, 2. Multiplying each of the subscripts in the empirical formula by 2 produces the molecular formula, CgHjgN 02. The common name for this culturally important compound is caffeine. 

A I he numbers of moles of the compounds in 100 g of water are obtained by dividing the mass of the compounds by their relative formula masses. The volumes of the solutions in dm arc obtained hy dividing the total mass bv the density. Dividing the numbers of moles of the halides by the volumes of their solutions gives the required molar concemralions. The answers are ... 

A. An organic compound with a formula mass of 417 was analyzed for ethoxyl (CH3CH20—) groups by the reactions... 

Formula mass The sum of the atomic masses of the atoms in a chemical compound or element. 

There are 69-7 g of gallium, Ga (atomic mass 69-7 amu), in a 145-g sample of gallium arsenide, GaAs. Note that l45 g is the formula mass for this compound. 

The mass of 1 mole of a compound is called its molar mass. If you write the molar mass of a compound without any units then it is the relative formula mass, often called the relative molecular mass (Mr). So the relative formula mass of water is 18. 

The following list tabulates the major reference masses (with their relative intensities and formulas) of the mass spectrum of heptacosafluorotributylamine.1 This is one of the most widely used reference compounds in mass spectrometry. 

Element Compound Relative Formula Mass Weight for 1000 pg/l (PPM)-g/l Solvent Note... 

O relative formula mass the sum of ail the relative atomic masses of aS the atoms or ions in a compound... 

To calculate a formula mass To calculate the percent composition by mass from the formula of a compound... 

The meaning of a chemical formula was discussed in Chapter 5, and we learned how to interpret formulas in terms of the numbers of atoms of each element per formula unit. In this chapter, we will learn how to calculate the number of grams of each element in any given quantity of a compound from its formula and to do other calculations involving formulas. Formula masses are presented in Section 7.1, and percent composition is considered in Section 7.2. Section 7.3 discusses the mole—the basic chemical quantity of any substance. Moles can be used to count atoms, molecules, or ions and to calculate the mass of any known number of formula units of a substance. Section 7.4 shows how to use relative mass data to determine empirical formulas, and the method is extended to molecular formulas in Section 7.5. 

The three types of formula masses correspond to the three types of formula units (1) atomic masses (also called atomic weights), (2) molecular masses (also called molecular weights), and (3) formula masses for ionic compounds (also called formula weights). The term atomic mass may be used whether an atom is combined or not, but it always refers to the mass of one atom of an element. 

The percentage of an element in a compound is 100% times the ratio of the total mass of the element divided by the formula mass. The percent composition of the compound is the percentages of all the elements. 

Avogadro s number was set at 6.0221367 X 10 so that the atomic mass of each element and the number of grams per mole of that element have the same numeric value, although in different units. The atomic mass of C is 12.00 amu, and 12.00 g is the mass of 1.000 mol of C. The formula mass of any compound or element is also equal to its number of grams per mole. The formula mass of a substance in units of grams per mole is called the molar mass of the substance. (Molar mass can be abbreviated MM.)... 

The percent composition of a compound can be calculated in terms of molar masses instead of formula masses. 

The formula mass (formula weight) of a substance is determined by adding the atomic masses (atomic weights) of each atom (not each element) in a formnla unit. Molecular mass is one type of formula mass (for substances that form molecnles) and is calculated in the same way as the formula mass for an ionic compound. For example, the formula mass of NH3 is 17.0 amu, the atomic mass of three hydrogen atoms plus that of one nitrogen atom. Three or more significant digits should be used to report formula masses. (Section 7.1)... 

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