Gram-formula mass

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 ... 

To calculate mass percent, you must know the mass of solute and the mass of solution. The molarity of the solution tells you the moles of solute per volume of solution. Stcirting with this information, you can convert to mass of solute by means of the gram formula mass (see Chapter 7 for details on calculating the grcim formula mass) ... 

Sample Calculate the gram formula mass of K2Cr207,... 

Mole is abbreviated mol. Do not use m or M for mole these symbols are used for other quantities related to moles, and so you will be confused if you use either of them. Note A mole is referred to by some authors as a gram molecular mass because 1 mol of molecules has a mass in grams equal to its molecular mass. In this terminology, a gram atomic mass is 1 mol of atoms, and a gram formula mass is 1 mol of formula units. 

Occasionally, one encounters gram-atomic mass (GAM), gram-formula mass (GFM), and gram-molecular mass (GMM). These terms are functionally the same as molar mass. For example, the GAM of an element is the mass in grams of a sample containing atoms and is equal to the element s atomic... 

A mole of iodine atoms is 126.9044 g of iodine, and a mole of iodine molecules (I.,) is 253.8088 g of iodine. Sometimes, to prevent confusion, a mole of atoms of an element is called a gram-atom. The mass of a mole of a compound for which a formula is written is sometimes taken to be the gram-formula-mass (gfm), the number of grams equal to the sum of the atomic masses corresponding to the formula, whether or not the formula is a correct molecular formula for the substance. Thus the molar mass of liquid acetic acid, for which the formula CH3COOH(l) is written, is taken... 

Example 11-2. What is the normality, for use as an oxidizing agent in acid solution, of a permanganate solution made by dissolving one-tenth of a gram formula mass of KMn04 (tVx 158.03 g) in water and diluting to a volume of 1 1 ... 

Solution. The reduction of permanganate ion in acid solution involves 5 electrons (Equation 11-11). Hence 1 gram formula mass is 5 equivalents. The solution is accordingly 0.5 N. 

The quotient of the gram formula mass of an acid by the number of hydrogen atoms which are replaceable for the reaction under consideration is called the equivalent mass of the acid. Likewise, the quotient of the gram formula mass of a base by the number of hydroxyl groups which are replaceable for the reaction under consideration is called the equivalent mass of the base. 

One equivalent mass of an acid neutralizes one equivalent mass of a base. It is important to note that the equivalent mass of a polyprotic acid is not invariant for H3PO4 it may be the gram formula mass, one half this, or one third, depending on whether one, two, or three hydrogens are effective in the reaction under consideration. 

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