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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.

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Presentation on theme: "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."— Presentation transcript:

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) + b. Formulas of acids: prefix hydro- indicates non- oxy-acid, (HCl, H 2 S etc). Formula of an oxy-acid is produced from the oxy-anion, by neutralizing the charge of the anion by H + ions. HCl(aq)  c. Ionic compounds are formed by combining positively-charged metal ion (or NH 4 + ) with a nonmetal or oxy- acid anion, so that the charge of the whole compound is neutral. 2. When the eq. is written, proceed with balancing it by changing the coefficients. Do not change subscripts in chemical formulas. Ca is in 2 nd group, produces Ca 2+ For the whole ionic compound to be neutral, two Cl - ions are needed. CaCl 2 (s) +H 2 (g) Hydrogen gas is not H, but H 2, because it occurs as such in nature. 2 Practice writing chemical formula of ionic compounds (next slide).

2 Formulas of Ionic Compounds 1. Find out the charge of anion or cation. a. If the cation is from group I or II, its charge is equal to the group number. Na (group I)  Na + Mg (group II)  Mg 2+ b. If the cation is transition metal, find its charge from the anion it is attached. Cu Cl 2 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, NH 4 + is the only positively-charged atomic group. Cl (group 7A or 17)  Cl - S (group 6A or 16 )  S 2- ? 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. NO 3 - SO 4 2- CO 3 2- PO 4 3- 2. Balance charges of cation and anion in the formula so that the ionic compound becomes electrically neutral. Practice: Sodium sulfate Na 2 SO 4 BaCO 3 Cu 3 PO 4 Cu 3 (PO 4 ) 2 Barium carbonate Copper (I) phosphate Copper (II) phosphate

3 If the reaction is uncompleted… 1. Recognize equation type. C 2 H 8 + O 2  Single displacement Double displacement Combination Decomposition a. Element + compound  (single displacement) b. Two ionic compounds  double displacement c. A complex molecule (+ a small molecule)  decomposition d. Two small molecules  combination H 2 O + CO 2 NaBr + Cl 2  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 unknown Generally, products are known only if oxidation: H 2 O + CO 2. AgNO 3 (aq) + CaCl 2 (aq)  CO 2 + H 2 O  h NaCl + Br 2 AgCl(s) + Ca(NO 3 ) 2 (aq) C 6 H 12 O 6 + O 2 2. Balance equation. 244 22 2 2 666 ? Remember this table. Cation Anions Cl - SO 4 2- PO 4 3- K + KCl K 2 SO 4 K 3 PO 4 H + HCl H 2 SO 4 H 3 PO 4 Zn 2+ ZnCl 2 ZnSO 4 Zn 3 (PO 4 ) 2 Al 3+ AlCl 3 Al 2( SO 4 ) 3 AlPO 4 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.


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