Calcium carbonate formula unit

FIGURE E.5 Each sample contains 1 mol of formula units of an ionic compound. From left to right are 58 g of sodium chloride (NaCl), 100 g of calcium carbonate (CaCO,), 278 g of iron(ll) sulfate heptahydrate (FeS04-7H.0), and 78 g of sodium peroxide (Na. O,). 

Bone is a porous tissue composite material containing a fluid phase, a calcified bone mineral, hydroxyapatite (HA), and organic components (mainly, collagen type). The variety of cellular and noncellular components consist of approximately 69% organic and 22% inorganic material and 9% water. The principal constiments of bone tissue are calcium (Ca ), phosphate (PO ), and hydroxyl (OH ) ions and calcium carbonate. There are smaller quantities of sodium, magnesium, and fluoride. The major compound, HA, has the formula Caio(P04)g(OH)2 in its unit cell. The porosity of bone includes membrane-lined capillary blood vessels, which function to transport nutrients and ions in bone, canaliculi, and the lacunae occupied in vivo by bone cells (osteoblasts), and the micropores present in the matrix. 

Calcium carbonate crystallizes in several different forms. In aragonite4 there are four formula units in an orthorhombic primitive unit cell with dimensions a = 4.94 x 10-10 m, b — 7.94 x 10 10 m and c — 5.72 x 10-10 m. 

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. 

The solution map begins with moles of calcium carbonate and ends with moles of oxygen. Determine the conversion factor from the chemical formula, which indicates three O atoms for every CaCOs unit. 

Many ionic compounds contain polyatomic ions. Table 2.5 shows some common polyatomic ions. Remember that the polyatomic ion stays together as a charged unit. The formula for potassium nitrate is KNO3 each K+ balances one NO3. The formula for sodium carbonate is Na2C03 two Na+ balance one CO. When two or more of the same polyatomic ion are present in the formula unit, that ion appears in parentheses with the subscript written outside. For example, calcium nitrate contains one Ca + and two N03 ions and has the formula Ca(N03)2. Parentheses and a subscript are only used if more than one of a given polyatomic ion is present thus, sodium nitrate is NaN03, not Na(N03). 

Again, consider the reaction of calcium hydroxide, Ca(OH)2, and sodium carbonate, Na2C03. Both are soluble ionic substances and therefore strong electrolytes when they dissolve in water, they go into solution as ions. Each formula unit of Ca(OH)2 forms one Ca ion and two OH ions in solution. If you want to emphasize that the solution contains freely moving ions, it would be better to write Cd (aq) + 20U aq) in place of Ca(OH)2(a ). Similarly, each formula unit of Na2C03 forms two Na ions and one CO- ion in solution, and you would emphasize this by writing 2Na (a ) + aq) in place of Na2C03(a ). The reaetant side of the equa-... 

However, there are still a large number of compounds in which atoms are not bound by covalent bonds but rather by ionic interactions or electrostatic interactions. These are ionic compounds typical examples include table salt NaCl (made of Na and Cl") and calcium carbonate (limestone, CaCOj). In these compounds no molecular species is found. The formula CaCOj simply implies that the compound consists of Ca ions and COj " ions in one-to-one ratio they are stacked together by the attractive forces between the positive and the negative electric charges and are arranged in an orderly manner (crystal). CaCOj would not behave as a unit like a molecule does. Hence the chemical properties of CaC03 are those associated with Ca and COj ". (I hasten to add, though, that the atoms in an ion, such as C03 , are bound by covalent bonds). So there are two types of compounds molecular compounds and ionic compounds. 

The molar mass (M) of a substance is the mass in granns of 1 mole of the substance. By definition, the mass of a mole of carbon-12 is exactly 12 g. Note that the molar mass of carbon is numerically equal to its atomic mass. Likewise, the atomic mass of calcium is 40.08 amu and its molar mass is 40.08 g, the atomic mass of sodium is 22.99 amu and its molar mass is 22.99 g, and so on. In general, an element s molar mass in grams is numerically equal to its atomic mass in atomic mass units. The molar mass (in grams) of any compound is numerically equal to its molecular or formula mass (in amu). The molar mass of watCT, for example, is 18.02 g, and the molar mass of sodium chloride (NaCl) is 58.44 g. 

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