Single 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 Caqueous 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 1 of 4 Double 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 OHions 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 H2O l SO2 g Sulfurous Acid H2SO3 aq Page 2 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 highest activity Li K Ca Na Mg Al Zn Cr Fe Cd Ni Sn Pb Cr 3 Fe 2 Ni 2 Sn 2 Pb 2 H2 Cu Cu 2 Ag Hg Hg 2 lowest activity Au Au 3 Page 3 of 4 Procedure 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 tingling sensations or see any color changes on your skin flush with water immediately for a minimum of 15 minutes Inform your instructor of any chemical contact as soon as possible Materials and Equipment Solids Copper metal zinc metal magnesium metal solid sodium bicarbonate Solutions 6M sodium hydroxide 6M hydrochloric acid 6M ammonium hydroxide 5 acetic acid all other solutions are 0 1M and include silver nitrate barium chloride sodium sulfate potassium chloride lead II nitrate iron III chloride sodium carbonate cobalt II nitrate sodium phosphate zinc nitrate copper II