Ionic Equations & Reactions

Equations Molecular equations – show the complete chemical formulas. Does not indicate ionic character Complete ionic equation – shows all ions. Actually how the particles exist in the solution

Steps for Writing Ionic Equations Write the balances molecular equation (balanced chemical equation) Break every thing down into its ions EXCEPT the solid, gas, water, or weak electrolyte (complete ionic equation) Cross out everything that is the same on both sides (spectator ions) Write what is left (net ionic equation)

Rules When writing ionic equations, you must keep together the solid, gas, water, or weak electrolyte Spectator ions – ions that appear on both sides of the equation. They have very little to do with the chemical reaction

Example Write the balanced chemical equation, the complete ionic equation, and the net ionic equation for the reaction between lead (II) nitrate and potassium iodide

Example Write the balanced chemical equation Pb(NO3)2 + 2 KI  PbI2 + 2 KNO3 You MUST identify the solid, gas, or water Pb(NO3)2 + 2 KI  PbI2 (s) + 2 KNO3 Balanced chemical equation

Example Now break every thing except the solid, gas, or water into its ions Remember ions are things with charges Everything will be broken down into one positive charge and one negative charge

Example Pb(NO3)2 + 2 KI  PbI2 (s) + 2 KNO3 Complete ionic Equation

Example Now cross out everything that is the same on both sides (spectator ions) Pb+2 + 2NO3-1 + 2K+1 + 2 I -1  PbI2 (s) + 2K+1 + 2NO3-1 Now write what is left Pb+2 + 2 I -1  PbI2 (s) Net ionic equation

Another Example Write the balanced chemical equation, complete ionic equation, and net ionic equation for the reaction between calcium chloride and sodium acetate

Another Example Balanced chemical equation CaCl2 + Na2CO3  CaCO3 (s) + 2NaCl Complete ionic equation Ca+2 + 2Cl -2 + 2Na +1 + CO3 -2  CaCO3 (s) + 2Na +1 + 2Cl -1 Net Ionic Equation Ca+2 + CO3 -2  CaCO3 (s)

What if water is formed? Write the balanced chemical equation, complete ionic equation, and net ionic equation for the reaction between Calcium hydroxide and nitric acid

Example with water 2(OH) -1 + 2H+1  2 HOH Balanced chemical equation Ca(OH)2 + 2 HNO3  Ca(NO3)2 + 2 HOH Complete ionic equation Ca+2 + 2(OH) -1 + 2H+1 + 2NO3 -1  Ca+2 + 2NO3 -1 + 2 HOH Net Ionic Equation 2(OH) -1 + 2H+1  2 HOH

5 Major Types of Reactions We will be discussing 5 major types of reactions Synthesis Decomposition Single Replacement Double Replacement Combustion You need to know these reactions! Note cards are an extremely effective way to remember them

Synthesis # 1 Metal oxide + nonmetal oxide  metal oxyanion (NO ions – No Redox) No Redox simply means that the oxidation numbers of the elements stays the same

Synthesis # 1 Example Sulfur dioxide gas is passed over solid calcium oxide SO2 + CaO  We know that we have to get a metal oxyanion. So we either get CaSO4 or CaSO3 We need to check the oxidation states on sulfur to see which one is the same.

Synthesis # 1 Example In SO2, the oxidation number of O is -2 So the oxidation number of S must be +4 Our product choices are CaSO3 or CaSO4 In CaSO3…S has an oxidation # of +4 In CaSO4…S has an oxidation # of +6 Therefore the product must be CaSO3 SO2 + CaO  CaSO3

Synthesis # 2 Metal oxide + water  strong base (IONS) Strong acids & bases ionize completely in water & are therefore electrolytes. They will be written as ions Strong bases…Group !a or 2A hydroxides There are 7 strong acids… HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4 You MUST know these!

Synthesis # 2 Example Solid sodium oxide is added to water Na2O + H2O  Na2O + H2O  NaOH Na2O + H2O  2NaOH Na2O stays together because it is solid H2O stays together because it is water NaOH is separated because it is a strong base Na2O + H2O  2Na+ + OH-

Synthesis # 3 Non metal oxide + water  oxyacid (weak molecules…strong ions…No Redox) Sulfur dioxide gas is placed in water SO2 + H2O  We are going to get an oxyacid…so we either have H2SO3 or H2SO4 The S needs to have the same oxidation number

Synthesis # 3 Example In SO2, O has an oxidation # of -2…so S has an oxidation # of +4 In H2SO3…S has an oxidation # of +4 In H2SO4…S has an oxidation # of +6 Therefore we will get In H2SO3 SO2 + H2O  H2SO3 Since H2SO3 is a weak acid…we will keep it together

Synthesis # 4 Metal + nonmetal  salt (NO ions) A salt is just an ionic compound ( a positive charge & a negative charge) Magnesium metal is combusted in nitrogen gas Mg + N2  Mg + N2  Mg3N2 3Mg + N2  Mg3N2

Decomposition # 1 Metal oxyanion  metal oxide + nonmetal oxide (No Redox – NO ions) A solid sample of calcium sulfate is heated CaSO4  CaSO4  CaO + SO3

Decomposition # 2 Base  metal oxide + water (No Redox – NO ions) Calcium hydroxide is decomposed Ca(OH)2  Ca(OH)2  CaO + H2O

Single Replacement # 1 Metal + ionic solution  Metal ion + metal (will have ions) Must look at activity series! Aluminum metal is added to a solution of copper (II) chloride Al + CuCl2  Al + CuCl2  AlCl3 + Cu 2Al + 3CuCl2  2AlCl3 + 3Cu 2Al + 3Cu +2  2Al +3 + 3Cu

Single Replacement # 2 Active metal (Group 1A, Ba, Ca, Sr) + water  H2 + strong base (IONS) Sodium is placed in water Na + H2O  Na + H2O  H2 + NaOH 2Na + 2H2O  H2 + 2NaOH 2Na + 2H2O  H2 + 2Na+ + 2OH-

Single Replacement # 3 Halogen + metal halide  new metal halide + halogen (REDOX…will have ions) Chlorine gas is bubbled into a solution of sodium bromide Cl2 + NaBr  Cl2 + NaBr  NaCl + Br2 Cl2 + 2NaBr  2NaCl + Br2 Cl2 + 2Br-  2Cl- + Br2

Double Replacement # 1 Precipitate (must know solubility rules)…the precipitate will stay together A saturated solution of barium hydroxide is mixed with a solution of iron (III) sulfate Ba(OH)2 + Fe2(SO4)3  Ba(OH)2 + Fe2(SO4)3  Fe(OH)3 + BaSO4(s) 3Ba(OH)2 + Fe2(SO4)3  2Fe(OH)3 + 3BaSO4(s) 3Ba+2 + 3SO4-2  3BaSO4(s)

Double Replacement # 2 Formation of a gas (acid + sulfide, carbonate, or bicarbonate) Hydrobromic acid is added to a solution of potassium bicarbonate HBr + KHCO3  HBr + KHCO3  H2CO3 + KBr H2CO3 ALWAYS breaks down into CO2 + H2O HBr + KHCO3 CO2 + H2O + KBr H+ + HCO3- CO2 + H2O

Double Replacement # 3 Metal hydride + water  H2 + strong base (IONS) Sodium hydride is placed into water NaH + H2O  NaH + H2O  H2 + NaOH NaH + H2O  H2 + Na+ + OH-

Combustion Hydrocarbon + O2 CO2+ H2O (No ions) Combustion of methane CH4 + O2 CO2+ H2O CH4 + 2O2 CO2+ 2H2O