Balancing Equations from scratch

1. Balancing Equations from scratch 1. If the eq. is given as text, write the formulas of all reactants and products, and given conditions. Calcium metal reacts with aqueous hydrochloric acid to produce aqueous calcium chloride and hydrogen gas. a. Formula of a metal is the symbol of the metal. Ca(s) + 2 HCl(aq)  CaCl2(s) + H2(g) b. Formulas of acids: prefix hydro- indicates non- oxy-acid, (HCl, H2S etc). Formula of an oxy-acid is produced from the oxy-anion, by neutralizing the charge of the anion by H+ ions. Ca is in 2nd group, produces Ca2+ For the whole ionic compound to be neutral, two Cl- ions are needed. Hydrogen gas is not H, but H2, because it occurs as such in nature. c. Ionic compounds are formed by combining positively-charged metal ion (or NH4+) with a nonmetal or oxy-acid anion, so that the charge of the whole compound is neutral. Practice writing chemical formula of ionic compounds (next slide). 2. When the eq. is written, proceed with balancing it by changing the coefficients. Do not change subscripts in chemical formulas.

2. Formulas of Ionic Compounds 1. Find out the charge of anion or cation. Na (group I)  Na+ Mg (group II)  Mg2+ a. If the cation is from group I or II, its charge is equal to the group number. b. If the cation is transition metal, find its charge from the anion it is attached. Cu Cl2 ? c. If the anion is derived from an atom, find its charge from its position in the periodic table. Halogen elements (fluorine group) and chalcogen elements (oxygen group) form anions with the charge of -1 and -2, respectively. Ammonium ion, NH4+ is the only positively-charged atomic group. Cl (group 7A or 17)  Cl - S (group 6A or 16 ) S2- There are two Cl ions, each of them with the charge of -1, hence the total negative charge is -2. One Cu ion must be +2 so that whole ionic compound is neutral. d. If the anion is a group of atoms, it is a oxy-anion. You must learn the charge of each oxy-anion. Practice: Sodium sulfate NO3- SO42- CO32- PO43- Na2SO4 Barium carbonate BaCO3 Copper (I) phosphate Cu3PO4 2. Balance charges of cation and anion in the formula so that the ionic compound becomes electrically neutral. Cu3(PO4)2 Copper (II) phosphate

3. Cation Anions Cl- SO42- PO43- K+KClK2SO4 K3PO4 H+ HCl H2SO4 H3PO4 Zn2+ ZnCl2 ZnSO4 Zn3(PO4)2 Al3+ AlCl3 Al2(SO4)3 AlPO4 Cations can have charges +1, +2 and +3. Anions can have charges -1, -2 and -3. Note how different charges of an cation are balanced by anions, and vice versa. Remember this table. If the reaction is uncompleted… 1. Recognize equation type. a. Element + compound  (single displacement) b. Two ionic compounds  double displacement c. A complex molecule (+ a small molecule)  decomposition Works only if the element in the elemental form is more reactive than that in compound; products: element2 + compound2 Works only if one of the products is either water, precipitate, or gas. Generally, products are: element2 + compound2 Generally, products are known only if oxidation: H2O + CO2. d. Two small molecules  combination 2 AgCl(s) + Ca(NO3)2(aq) 2 AgNO3(aq) + CaCl2(aq) Generally, products are unknown hn 6 6 6 C6H12O6 + O2 CO2 + H2O  2. Balance equation. ? Single displacement Combination C2H8 + O2 4 4 H2O + CO2 2 2 NaBr + Cl2 2 NaCl + Br2 Double displacement Decomposition