Ionic compounds 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. 

Ionic Compounds, Formula Units, and Formula Mass... 

The mass of a water molecule can be correctly referred to as a molecular mass. The mass of one NaCl formula unit, on the other hand, is not a molecular mass, because NaCl is an ionic compound. The mass of any unit represented by a chemical formula, whether the unit is a molecule, a formula unit, or an ion, is known as the formula mass. The formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of aii atoms represented in its formuia. 

The molar mass of a molecular compound is the mass per mole of its molecules. The molar mass of an ionic compound is the mass per mole of its formula units. 

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. 

The molar mass of an element is the mass per mole of its atoms the molar mass of a molecular compound is the mass per mole of its molecules the molar mass of an ionic compound is the mass per mole of its formula units. The units of molar mass in each case are grams per mole (g-moD1). 

The molar masses of molecular and ionic compounds are calculated from the molar masses of the elements present the molar mass of a compound is the sum of the molar masses of the elements that make up the molecule or the formula unit. We need only note how many times each atom or ion appears in the molecular formula or the formula unit of the ionic compound. For example, the molar mass of the ionic compound Na2S04 is... 

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 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)... 

Molecular formulas give all the information that empirical formulas do, plus the ratio of the number of moles of each element to the number of moles of the compound. (Molecular formulas are used only for molecular substances, not ionic substances.) A molecular formula can be determined from the empirical formula of the compound and its formula mass First, divide the formula mass by the mass in amu of one empirical formula unit, which will result in a small integer. Then, multiply each subscript of the empirical formula by that integer. (Section 7.5)... 

What is a synonym for molar mass (a) for molecules (b) for atoms (c) for ionic compounds What is a synonym for formula mass (d) for molecules (e) for atoms (f) for ionic compounds ... 

The formula mass of a compound is the sum of the atomic masses (Chap. 3) of all the atoms (not merely each kind of atom) in the formula. Thus, in the same way that a symbol is used to represent an element, a formula is used to represent a compound or a molecule of an element, such as H2, and also one unit of either. The formula mass of the substance or the mass of 1 mol of the substance is easily determined on the basis of the formula (Sec. 7.4). Note that just as formula unit may refer to uncombined atoms, molecules, or atoms combined in an ionic compound, the term formula mass may refer to the atomic mass of an atom, the molecular mass of a molecule, or the formula mass of a formula unit of an ionic compound. 

An element s most stable ion forms an ionic compound with bromine, having the formula XBr2. If the ion of element X has a mass number of 230 and 86 electrons, what is the identity of the element, and how many neutrons does it have ... 

Some substances exist as a collection of ions rather than as separate mol- ecules. An example is ordinary table salt, sodium chloride (NaCl), which is composed of an array of Na+ and Cl- ions. There are no NaCl molecules present. However, in this text, for convenience, we will apply the term molar mass to both ionic and molecular substances. Thus we will refer to 58.44 (22.99 + 35.45) as the molar mass for NaCl. In some texts the term formula weight is used for ionic compounds instead of the terms molar mass or molecular weight. ... 

When aluminum metal is heated with an element from Group 6A of the periodic table, an ionic compound forms. When the experiment is performed with an unknown Group 6A element, the product is 18.56% A1 by mass. What is the formula of the compound ... 

This tells us that 2 molecules of hydrogen chloride (in hydrochloric acid) will react with 1 formula unit of calcium carbonate (as it contains a metal it must be an ionic compound), but it does not tell us how much hydrogen chloride in grammes we must add to the calcium carbonate to ensure that all the calcium carbonate is used up. But if we use moles all is much clearer. The relative formula mass of calcium carbonate is 40 (from calcium) -1-12 (from carbon) -I- (3 X 16) (from oxygen) = 100. So 1 mole of calcium carbonate has a mass of 100 g. Then for every 100 g of calcium carbonate we are reacting we will need to use 2 x 36.5g(=73g) of hydrogen chloride. 

Scientists also use the simplest formula to represent one mole of an ionic compound. They often use the term formula unit when referring to ionic compounds, because they are not found as single molecules. A formula unit of an ionic compound represents the simplest ratio of cations to anions. A formula unit of KBr is made up of one ion and one Br ion. One mole of an ionic compound has 6.022 x 10 of these formula units. As with molecular compounds, the molar mass of an ionic compound is the sum of the masses of all the atoms in the formula expressed in g/mol. Table 1 compares the formula units and molar masses of three ionic compounds. Sample Problem F shows how to calculate the molar mass of barium nitrate. 

Why is the simplest formula used to determine the molar mass for ionic compounds ... 

An ionic compound used as a chemical fertilizer has the composition (by mass) 48.46% O, 23.45% P, 21.21% N, 6.87% H. Give the name and chemical formula of the compound and draw Lewis diagrams for the two types of ions that make it up. 

We have already discussed that fact that you can find the atomic masses for each of the elements on the Periodic Table of Elements. In this lesson, we will examine the process of taking these individual elemental masses and determining the mass of a compound. In reality, you have already needed to do some of these calculations, but now we will cover them formally. When dealing with molecular compounds we talk about molecular mass. The molecular mass is the mass of one molecule of a molecular compound. When we are dealing with an ionic compound, we can t use the term molecular mass, because ionic compounds are not made up of individual molecules. For ionic compounds, we use the term formula mass, which is the mass of one formula unit. The term formula unit refers to the simplest ratio of the cations to anions that are found in the compound. NaCl, the formula unit of table salt, for example, indicates that there is one Na+ ion for every Cl ion. 

Although the terms molecular mass and formula mass are different, and they really do represent different concepts, the method for calculating each is identical. In fact, you might not even know if the particular compound that you are calculating the mass for is molecular or ionic, but you can still get the correct value. Don t get thrown off by the language in the questions that you are asked to answer. If the question asks for the molecular mass, that is simply an indication that you are working with a molecular compound. If the question refers to formula mass, it is simply noting that the compound is ionic. 

Formula mass The mass of one formula unit of an ionic compound. 

The physical appearance of one mole of each of some compounds is illustrated in Figure 2-11. Two different forms of oxalic acid are shown. The formula unit (molecule) of oxalic acid is (COOH)2 (FW = 90.0 amu molar mass = 90.0 g/mol). When oxalic acid is obtained by crystallization from a water solution, however, two molecules of water are present for each molecule of oxalic acid, even though it appears dry. The formula of this hydrate is (COOH)2 2H2O (FW = 126.1 amu molar mass = 126.1 g/mol). The dot shows that the crystals contain two H2O molecules per (COOH)2 molecule. The water can be driven out of the crystals by heating to leave anhydrous oxalic acid, (COOH)2. Anhydrous means without water. Copper(II) sulfate, an ionic compound, shows similar behavior. Anhydrous copper(II) sulfate (CuSO FW = 159.6 amu molar mass = 159.6 g/mol) is almost white. Hydrated copper(II) sulfate (CuSO 5H2O FW = 249.7 amu molar mass = 249.7 g/mol) is deep blue. The following example illustrates how we might find and use the formula of a hydrate. 

As you learned in Chapter 4, covalent compounds are composed of molecules, and ionic compoimds are composed of formrda units. The molecular mass of a covalent compoimd is the mass in atomic mass emits of one molecule. Its molar mass is the mass in grams of 1 mol of its molecules. The formula mass of an ionic compound is the mass in atomic mass emits of one formeila unit. Its molar mass is the mass in grams of 1 mol of its formula emits. How to calceilate the molar mass for ethanol, a covalent compoemd, and for calcieun chloride, an ionic compound, is shown below. 

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