KEY Activity 151-6 Predicting Products of Double Displacement Reactions Directions: This GLA worksheet is focused on predicting products and writing balanced equations for double displacement reactions. Part A introduces splitting up aqueous ionic compounds, as well as acids and bases into their respective aqueous ions. Part B discusses creating products, or switching partners, from two aqueous compounds. Part C discusses determining solubility and the phases of the products. The worksheet is also accompanied by instructional videos. See http://www.canyons.edu/departments/chem/gla for additional materials. *This GLA is closely related to writing ionic compounds and balancing chemical reactions. For additional help, refer to the GLA 151-3 and GLA 151-5 activities.* Part A Identifying ions in aqueous compounds Aqueous ionic compounds, acids, and bases will split up into their respective ions in solution. Below is a summary of ions that could be generated from these three classes of compounds. Keep in mind that polyatomic ions stay as one unit in solution and do not split up into their individual atoms. For additional guidance, consult the Ionic Compounds GLA activity. a) Aqueous ionic compounds will split into their cation and anion in solution. The charge of most ions can be predicted from the periodic table, or from the identity of the polyatomic ion. For those cations that form more than one charge, the charge should be determined from the ions paired anion(s). b) Strong acids will split up into H + ion(s) and an anion (either a nonmetal ion or a polyatomic ion). c) Strong bases will typically split up into OH - ion(s) and a cation. Split the following reactants into their respective ions. We can ignore the subscripts for now and just focus on the individual ions that are generated. Practice: a) Pb(NO 3) 2(aq) + LiCl(aq) Pb 2+ NO 3 - Li + Cl - b) HCl(aq) + NaOH(aq) H + Cl - Na + OH - Activity 151 6 Page 1 of 6
Example #1: a) AgC 2H 3O 2(aq) + Na 2SO 4(aq) b) H 2SO 4(aq) + Ba(OH) 2(aq) Part B Forming products ( switching partners ). When two aqueous compounds are mixed together, their respective ions will be able to interact and switch partners. When one of the possible products is a solid (s), liquid (l), or gas (g), a reaction has occurred. The example below shows what occurs when Pb(NO 3) 2 (aq) is mixed with LiCl (aq). The Pb 2+ ion is now able to react with the Cl - ion and the Li + ion is now able to react with NO 3 - ion. We will discuss phases in Part C. When the compounds switch partners, the products that are formed will depend on the charges of the ions. Keep in mind that cations will react with anions in a ratio that will cancel out their charges. When H + (aq) reacts with OH - (aq), it produces H 2O (l). For the following problems, indicate which ions will react with each other and write the newly formed compounds as products in the reaction. Practice: a) Pb(NO 3) 2(aq) + LiCl(aq) PbCl 2 + LiNO 3 Pb 2+ NO 3 - Li + Cl - b) HCl(aq) + NaOH(aq) H 2O + NaCl H + Cl - Na + OH - Activity 151 6 Page 2 of 6
Example #2: a) MgSO 4(aq) + CaCl 2(aq) + b) HNO 3(aq) + Ba(OH) 2(aq) + Part C Determining the phases of the products (s, l, g, aq). For a reaction to occur, some chemical or physical change must occur. Most often, this change is associated with a change in phase. After forming the products, the phases for ionic compounds are determined by using the solubility rules, shown in the table below. What you are looking for is if your ionic compound has any of the ions in the left-hand column. The top table shows the ions that are mostly soluble and the exceptions. The bottom table shows the ions that are mostly insoluble and the exceptions. Recall that compounds that are soluble are aqueous (aq) and compounds that are insoluble are solid (s). Water that is formed in acid/base reactions is typically a liquid (l). When both of the possible products are soluble, or (aq), then they both remain in solution and no reaction occurs. In these cases, we write No Reaction or NR instead of writing the predicted products. Activity 151 6 Page 3 of 6
Practice: Determine the phase of the following ionic compounds: a) AgCl(s) According to the solubility rules, Cl - is soluble, but when it is bound to Ag +, it is an exception, so AgCl is insoluble. Insoluble compounds are in solid phase (s). b) Na 2SO 4(aq) According to the solubility rules, Na + is always soluble with no exceptions, so Na 2SO 4 is soluble. Soluble compounds are in aqueous phase (aq). Example #3: Determine the phase of the following ionic compounds: a) CaCO 3( ) b) Ba(NO 3) 2( ) Part D Writing complete molecular equations, predicting products and including phases. After the products are predicted and the phases of each of the products determined, the complete chemical equation can be written and balanced. Refer to the Balancing Chemical Equations GLA for additional guidance. Practice: Balance the equation below and use the solubility rules to determine the phases of the products. a) BaCl 2(aq) + K 2SO 4(aq) 2 KCl(aq) + BaSO 4(s) According to the solubility rules, any ionic compound with K + is always soluble with no exceptions so it is aqueous, (aq). Although ionic compounds with SO 4 2- are mostly soluble, Ba 2+ is an exception, which makes BaSO 4 insoluble, (s). Predict the products of the following reactants, balance the completed equation, and determine the phases of the products: b) 2 HBr(aq) + Sr(OH) 2(aq) 2 H 2O(l) + SrBr 2(aq) According to the solubility rules, compounds with Br - are soluble and Sr 2+ is not an exception, so SrBr 2 is aqueous, (aq). The product, water (H 2O), in an acid/base reaction is typically a liquid, (l). Activity 151 6 Page 4 of 6
Example #4: Balance the chemical equation below and use the solubility rules to determine the phases of the products. a) H 2SO 4(aq) + NH 4OH(aq) (NH 4) 2SO 4( ) + H 2O( ) Example #5: Predict the products of the following reactants, balance the completed equation, and determine the phases of the products: a) MgSO 4(aq) + Ca(NO 3) 2(aq) b) CaCl 2 (aq) + NH 4NO 3 (aq) Activity 151 6 Page 5 of 6
Part E Extra Practice 1. Determine the phases of the following ionic compounds: a) Ca(C 2H 3O 2) 2 b) Ag 2SO 4 c) PbBr 2 d) (NH 4) 3PO 4 e) CaS f) Hg 2Cl 2 g) KOH h) Sr(NO 3) 2 i) Na 2CO 3 j) NH 4OH 2. Predict the products for the following reactions. Include all phases and balance the chemical reactions. a) AgC 2H 3O 2(aq) + Na 2SO 4(aq) b) H 2SO 4(aq) + Ba(OH) 2(aq) c) AgNO 3(aq) + KCl(aq) d) BaCl 2 (aq) + KNO 3(aq) e) HBr(aq) + NH 4OH(aq) f) Sr(NO 3) 2(aq) + Na 3PO 4(aq) g) CaS(aq) + MgCl 2(aq) h) HCl (aq) + Cu(C 2H 3O 2) 2 (aq) i) (NH 4) 2CO 3(aq) + BaCl 2(aq) j) Challenge: Ca (s) + H 2O (l) Activity 151 6 Page 6 of 6