Atoms must be conserved! Balancing equations Atoms must be conserved!

Balancing equations What you learn in this section: How to balance simple equations. Tests for anions (negative ions) Chlorides Cl- Sulfates SO42- and Sulfites SO32- Carbonates CO32- and hydrogencarbonates HCO3- Nitrates NO3- Phosphates PO43-

Balancing equations The law of conservation of mass states the total mass of the products in chemical reaction = to the total mass of the reactants. Law of Conservation of Matter states in any chemical reaction matter is neither created or destroyed but is changed from one form to another.

Balancing equations Counting Atoms How many atoms of each element are in the following molecules? 1. H2SO4 2. Ca(OH)2 3. NaCl 4. (NH3)3P04 5. 3H2O 6. 4Al2(CO3)3 5/17/2018

Balancing equations Answers 1. 2 hydrogen, 1 sulfur, 4 oxygen 2. 1 calcium, 2 oxygen, 2 hydrogen 3. 1 sodium, 1 chlorine 4. 3 nitrogen, 9 hydrogen, 1 phosphorus, 4 oxygen 5. 6 hydrogen, 3 oxygen 6. 8 aluminum, 12 carbon, 36 oxygen

Balancing equations A chemical equation is a way of representing a chemical change. It shows reactants and products. To balance an equation means to change the numbers of each molecule involved, so that the same number of atoms of each element appear on the reactants side and on the products side. Chemical equations balance on an atomic level, not molecular.

Balancing equations You cannot change the formula of a substance, i.e. if the equation has NH3 you cannot change this you can only put a number in front of it, 2NH3, increasing the number of N’s and the number of H’s. Never change the subscripts (small numbers). It is possible to write balanced equations for lots of reactions but that does not mean that the reaction actually takes place.

Balancing equations Is this equation balanced? NaCl + H2O  NaOH + Cl2 left side has 1Na, 1Cl, 2H, and 1O right side has 1Na, 1O, 1H, and 2Cl NO!!!!!! It is not balanced!! 5/17/2018

Balancing equations Yes!!!!!! It is balanced!! HCl + NaOH NaCl+ H2O left side has 2H, 1Cl, 1Na, and 1O right side has 1Na, 1Cl, 2H, and 1O Yes!!!!!! It is balanced!! 5/17/2018

Balancing equations Is this equation balanced? Ca + H2O Ca(OH)2 + H2 left side has 1Ca, 2H, 1O right side has 1Ca, 2O, 4H No!!!!!! It is not balanced!! How can we make it balance???? 5/17/2018

Balancing equations Ca + H2O  Ca(OH)2 + H2 We need more H’s, but we can’t add just the H atom, we have to add the entire molecule the H is attached to: Putting a 2 in front of the H2O gives 1 Ca + 2 H2O  1 Ca(OH)2 + 1 H2

Balancing equations 1 Ca + 2 H2O  1 Ca(OH)2 + 1 H2 Just like in math, this equation may be written in a simpler way: Ca + 2 H2O Ca(OH)2 + H2 (be sure you write the “2” on your worksheet!)

Balancing equations What is balanced in a chemical equation? Three things are balanced in a chemical equation: 1. Atoms 2. Mass 3. Charge

For now, you will only be concerned with balancing atoms For now, you will only be concerned with balancing atoms. Remember, the number of atoms of each element on the reactants side must equal the number of atoms of each element on the products side! When we do redox equations we will need to balance the electrons too.

Balancing equations Balance the following

Balancing equations Balance the following NaPO3 + CuO -> NaCuPO4 SO3 + H2O -> H2SO4 Be(OH)2 -> BeO + H2O BaO + H2O -> Ba(OH)2 Na2SO3 + S -> Na2S2O3 SO2 + H2O -> H2SO3 Li2O + H2O -> LiOH Na2HPO4 -> Na4P2O7 + H2O H4As2O7 -> As2O5 + H2O CaC2 + N2 -> CaCN2 + C HAsO3 -> As2O5 + H2O

Tests for Anions Anion test observation inference Chloride Add a few drops of AgNO3 to a soln. of the solid White ppt formed that is soluble in ammonia soln. Ag+ + Cl-  AgCl Sulfate or Sulfite 1. add BaCl2 soln. to a soln. of the solid 2.add dil HCl 1. white ppt formed. 2. ppt disolves = sulfite, or ppt remains = sulfate. Ba2+ + SO42-  BaSO4 or Ba2+ + SO32-  BaSO3 BaSO4 + HCl no reaction or BaSO3 +2HClBaCl2 +SO2 +H2O

Tests for Anions Anion test observation inference Nitrate To a soln of the solid add freshly made FeSO4 soln then add conc H2SO4 BROWN RING TEST A brown ring is formed at the junction between the two liquids. Brown ring due to presence of the nitrate ion. phosphate Ammonium molybdate added to a soln of the solid. Conc. HNO3 added and the soln warmed Yellow ppt is formed. Phosphate ions are present.

Tests for Anions Anion test observation inference Carbonate CO32- Hydrogen-carbonate HCO3- 1. add dilute HCl to the solid. Fizzing, gas given off that turns limewater milky CO32-+2H+CO2+H2O HCO3-+H+CO2+H2O Limewater Ca(OH)2+CO2 CaCO3+H2O 2. add MgSO4 to a fresh soln of the solid. White ppt  carbonate no. ppt.  hydrogencarbonate. Boiling gives a ppt. Mg2++CO32-MgCO3 Mg2++HCO3- Mg(HCO3)2 Boiling Mg(HCO3)2MgCO3+ CO2+H2O