Page 1 of 4Single and Double Displacement Reactions Objectives The objectives of this lab are: a) To perform and observe the results of a variety of single and double displacement reactions, b) To become familiar with some of the observable signs of these reactions, c) To identify the products formed in each of these reactions, d) To write balanced chemical equations for each single and double displacement reaction studied. Background During a chemical reaction both the form and composition of matter are changed. Old substances are converted to new substances, which have unique physical and chemical properties of their own. Some of the observable signs that a chemical reaction has occurred include the following: • A metallic deposit appears • Bubbles appear • A temperature change occurs • A color change occurs • A precipitate (cloudy, tiny particles) appears Note that there are many other observable signs for chemical reactions, but these are the ones most likely to be encountered in this lab. Single Displacement Reactions All single displacement reactions have the general form: A + BC → B + AC Here, A is an element and BC is usually an aqueous ionic compound or an acid (consisting of B+ and C- aqueous ions). A displaces B in BC, resulting in the formation of a new element B and a new ionic compound or acid, AC. If the new element B is a metal, it will appear as a metallic deposit. If it is a gas, it will appear as bubbles. An Activity Series of elements is often used to determine if A will displace B in a single displacement reaction. An Activity Series is provided at the end of the Background section. As a rule, if A has a higher activity that B, a single displacement reaction will occur. However, if A has lower activity than B, a single displacement reaction will not occur. Example 1: magnesium metal + aqueous aluminum chloride Since Mg is more active than Al, a single displacement reaction will occur. The predicted products are aluminum metal and aqueous magnesium chloride Reaction Equation: 3 Mg (s) + 2 AlCl3 (aq) → 2 Al (s) + 3 MgCl2 (aq)Page 2 of 4Double Displacement Reactions All double displacement reactions have the general form: AB + CD → AD + CB Reactions that can be classified as double displacements include precipitation reactions, neutralization reactions and gas forming reactions. Precipitation Reactions Here AB and CD are usually aqueous ionic compounds (or acids) consisting of aqueous ions (A+ and B-, C+ and D-). When a double displacement reaction occurs, the cations and anions switch partners, resulting in the formation of two new ionic compounds AD and CB, one of which is in the solid state. This solid product is an insoluble ionic compound called a precipitate. To determine whether a product ionic compound will be soluble or insoluble, consult the Solubility Rules provided at the end of the Background section. Note that if both of the predicted products are soluble, a precipitation reaction will not occur. Example 2: aqueous lead(II) nitrate + aqueous potassium chloride The predicted products are lead(II) chloride (insoluble) and potassium nitrate (soluble). Since one of the predicted products is insoluble, a precipitation reaction is will occur. Reaction Equation: Pb(NO3)2 (aq) + 2 KCl (aq) → 2 KNO3 (aq) + PbCl2 (s) Neutralization Reactions Here AB is an acid (consisting of H+ and X- aqueous ions) and BC is a base (consisting of M+ and OH- ions). When a double displacement reaction occurs, the cations and anions switch partners, resulting in the formation of water and a new ionic compound (or salt), which is usually soluble. Neutralization reactions are exothermic, and are generally accompanied by a noticeable release of heat. Example 3: sulfuric acid + aqueous lithium hydroxide The predicted products are water and lithium sulfate. Reaction Equation: H2SO4 (aq) + 2 LiOH (aq) → Li2SO4 (aq) + 2 H2O (l) Gas Forming Reactions In these reactions one of the products (AD or CB) after the double displacement is in the gaseous state. One such example is hydrogen sulfide (H2S). However, one of the products could also be carbonic acid (H2CO3) or sulfurous acid (H2SO3). Both carbonic acid and sulfurous acid are unstable and will decompose to form carbon dioxide and sulfur dioxide gases, respectively: Carbonic acid H2CO3 (aq) → H2O (l) + CO2 (g) Sulfurous Acid H2SO3 (aq) → H2O (l) + SO2 (g)Page 3 of 4 Example 4: nitric acid + aqueous sodium sulfite The predicted products are sulfurous acid and sodium nitrate. However sulfurous acid decomposes to sulfur dioxide and water: Reaction Equation: 2 HNO3 (aq) + Na2SO3 (aq) → 2 NaNO3 (aq) + H2SO3 (aq) decomposes Final Equation: 2 HNO3 (aq) + Na2SO3 (aq) → 2 NaNO3 (aq) + H2O (l) + SO2 (g) Writing Equations for Reactions • Write the correct formulas for each reactant and place a yield arrow (→) after the last reactant. • Identify the reaction type – single or double displacement, using the guidelines outlined thus far. • If you determine that a reaction will occur, write the correct formula(s) of the products after the arrow. If you determine that a reaction will not occur, simply write “no reaction” after the arrow. • Balance the equation (to ensure mass conservation). • Be sure to include the physical states of all reactants and products in your final equation. Solubility Rules and Activity Series SOLUBILITY RULES 1. Alkali metal compounds, acetates, nitrates, and ammonium compounds are all soluble. 2. Hydroxides of alkali metals and NH4+1, Ca+2, Sr+2, and Ba+2 are soluble. All others are insoluble. 3. All halides (chlorides etc.) are soluble except for those containing Ag+1, Pb+2, and Hg2+2. 4. Most sulfates are soluble, except for BaSO4, SrSO4, Ag2SO4, PbSO4, and CaSO4. 5. Most phosphates, carbonates, chromates and sulfides are insoluble (except those of the alkali metals and ammonium). 6. In addition, all acids are soluble! ACTIVITY SERIES Li K Ca highest activity Na Mg Al Zn Cr → Cr+3 Fe → Fe+2 Cd Ni → Ni+2 Sn → Sn+2 Pb → Pb+2 H2 Cu → Cu+2 Ag Hg → Hg+2 lowest activity Au → Au+3Page 4 of 4Procedure Safety Be especially cautious when using the 6M HCl and 6M NaOH as they can burn your skin. Also be aware that skin discoloration will result from contact with AgNO3. If you feel any