Reactions in Aqueous Solution

Single Replacement A lone metal, (or hydrogen or halogen) replaces another metal (or hydrogen or halogen) AB + C → A + CB HCl + Mg  H2 + MgCl2

Single Replacement Usually results in the formation of a solid (metal) but can produce a gas (hydrogen) or a halogen

Single Replacement Single replacement reactions will only proceed if the lone element is MORE ACTIVE than its counterpart in the compound Use the Activity Series of Metals (or Halogens)

Activity Series of Metals Li – Lithium (most active) K – Potassium Ca – Calcium Li – Na will replace H from water & acids Na – Sodium Mg – Magnesium Al – Aluminum Zn – Zinc Mg – Pb will replace H from acids only Fe – Iron Pb – Lead H – Hydrogen Cu – Copper Ag – Silver Cu and below cannot replace H at all Au – Gold

Activity Series of Metals When predicting the products of a single replacement reaction with a metal, remember the charges of the ions, and criss-cross! EX: K + MgSO4  ??? K replaces Mg K is +1 and SO4 is -2 so…. Mg + K2SO4 are the products

Activity Series of Halogens F – Fluorine (most active) Cl – Chlorine Br – Bromine I – Iodine At – Astatine ALL Halogens are DIATOMIC!

Activity Series of Halogens *Remember* All halogens are -1 charge and diatomic when alone EX: F2 + NaCl  ??? F will replace Cl Na (+1) and F (-1) charge so… Cl2 + NaF are the products

Single Replacements Try these: H2 + NaCl  ????? Fe + CuNO3  ????? NO REACTION! (Na is higher than H) Fe + CuNO3  ????? Cu + Fe(NO3)2 (assume Fe+2) Balance the equation… Cl2 + MgBr2  ??? MgCl2 + Br2 (already balanced)

AB + CD → AD + CB Two ionic compounds react by exchanging cations Double Replacement Two ionic compounds react by exchanging cations AB + CD → AD + CB AgNO3 + NaCl → AgCl + NaNO3

Aqueous Solutions Many important reactions take place in water Ionic compounds dissociate in aqueous solutions These solutions contain free cations and anions

Complete Ionic Equation An equation that shows dissolved ionic compounds as their free ions AgNO3 (aq)+ NaCl (aq)→ AgCl (s) + NaNO3 (aq) Ag+ + NO3- + Na+ + Cl- → AgCl (s) + Na+ + NO3-

Complete Ionic Equation The equation can be simplified by eliminating ions that do not participate in the reaction. Ions that appear on both sides of the equation can be cancelled out These ions that are not directly involved in a reaction are called spectator ions

Complete Ionic Equation AgNO3 (aq)+ NaCl (aq)→ AgCl (s) + NaNO3 (aq) Ag+ + NO3- + Na+ + Cl- → AgCl (s) + Na+ + NO3- Ag+ + Cl- → AgCl (s)

Ag+ (aq) + Cl- (aq) → AgCl (s) Net Ionic Equation The equation that indicates only those particles that actually take part in a reaction is the net ionic equation Ag+ (aq) + Cl- (aq) → AgCl (s)

Double Replacement: Generally one of these is true: One product is a precipitate (s). One product is a gas (g) that bubbles out of mixture One product is a molecular compound such as water

Double Replacement: If neither product is a (s), (g) or H2O, both products will be aqueous (aq) & soluble – this means you only have a mixture and there is NO REACTION. Means you do NOT have to balance the equation b/c there is no chemical reaction taking place!

Double Replacement: You can determine the solubility of a compound usually by the anion – certain anions are usually soluble (aq) (like nitrates & chlorates) & others are usually insoluble (s) (like carbonates & hydroxides)

Double Replacement: Some cations can be used to determine the solubility of a compound – alkali metal (Li, Na, K) & ammonium compounds are going to be soluble with very few exceptions

Solubility Rules: Compounds Solubility Exceptions . Salts of alkali metals and ammonia Soluble (aq) Few exceptions Nitrate salts and chlorate salts Sulfate salts Compounds of Pb, Ag, Hg, Ba, Sr, and Ca (s) Chloride salts Compounds of Ag and some compounds of Hg and Pb (s) Carbonates, phosphates, chromates, sulfides, and hydroxides Most are insoluble Compounds of the alkali metals and of ammonia (aq)

Let’s try an example: NaOH(aq) + CaCl2(aq)  ??? + ??? Na and Ca switch places, so… Ca(OH)2 + NaCl (products) Are either of these insoluble? YES! Ca(OH)2 is insoluble (s) NaOH(aq) + CaCl2(aq)  Ca(OH)2(s) + NaCl(aq) Now balance the equation.

Let’s try an example: NaOH(aq) + KCl(aq)  ??? + ??? Na and K switch places, so… KOH + NaCl (products) Are either of these insoluble? NO! Both are soluble (aq) [alkali metals] NaOH(aq) + KCl(aq)  NO REACTION

Let’s try an example: NaOH(aq) + HCl(aq)  ??? + ??? Na and H switch places, so… HOH + NaCl (products) Are either of these insoluble? No BUT… HOH is water!!! NaOH(aq) + HCl(aq)  HOH(l) + NaCl(aq) Balance the equation.