Precipitation Reactions PDF

🧪 Precipitation Reactions and Net Ionic Equations Determining Products in Precipitation Reactions  Precipitation reactions are double replacement reactions.  The first and last ions pair together, as do the two middle ions. Example: Silver nitrate (AgNO3AgNO3) reacts with calcium chlori...

🧪 Precipitation Reactions and Net Ionic Equations Determining Products in Precipitation Reactions  Precipitation reactions are double replacement reactions.  The first and last ions pair together, as do the two middle ions. Example: Silver nitrate (AgNO3AgNO3) reacts with calcium chloride (CaCl2CaCl2). 1. Identify the charges of the ions: o Silver (AgAg) has a +1 charge because nitrate (NO3NO3) has a -1 charge. o Chloride (ClCl) has a -1 charge (halogens typically have -1 charges). o Calcium (CaCa) has a +2 charge. 2. Pair the ions: o Silver (Ag+Ag+) pairs with chloride (Cl−Cl−) to form silver chloride (AgClAgCl). o Calcium (Ca2+Ca2+) pairs with nitrate (NO3−NO3−) to form calcium nitrate (Ca(NO3)2Ca(NO3)2). Crisscross Method: Use the crisscross method to write the formula. For example, with CaCa and NO3NO3: Ca1(NO3)2Ca1(NO3)2, which simplifies to Ca(NO3)2Ca(NO3)2. When there are multiple polyatomic ions, enclose them in parentheses. 3. Balanced equation: 2AgNO3+CaCl2→2AgCl+Ca(NO3)22AgNO3+CaCl2 →2AgCl+Ca(NO3)2 Determining Phases  Nitrates (NO3NO3) are always soluble (aqueous phase).  Chlorides (ClCl) are generally soluble, except for silver (AgAg), mercury (HgHg), and lead (PbPb). Example: In the reaction 2AgNO3(aq)+CaCl2(aq)→2AgCl(s)+Ca(NO3)2(aq)2AgNO3(aq)+CaCl2 (aq)→2AgCl(s)+Ca(NO3)2(aq):  AgNO3AgNO3 is aqueous because nitrates are always soluble.  CaCl2CaCl2 is aqueous because chlorides are generally soluble.  AgClAgCl is solid because silver chloride is an exception to the solubility of chlorides. Total Ionic Equation  Separate each substance in the aqueous phase into its ions. Leave solids, liquids, and gases as they are.   For 2AgNO3(aq)+CaCl2(aq)→2AgCl(s)+Ca(NO3)2(aq)2AgNO3(aq)+CaCl2 (aq)→2AgCl(s)+Ca(NO3)2(aq): 2Ag+(aq)+2NO3−(aq)+Ca2+(aq)+2Cl−(aq)→2AgCl(s)+Ca2+(aq)+2NO3−(aq)2A g+(aq)+2NO3−(aq)+Ca2+(aq)+2Cl−(aq)→2AgCl(s)+Ca2+(aq)+2NO3−(aq) Spectator Ions Spectator ions are ions that appear unchanged on both sides of the total ionic equation. They do not participate in the reaction. Example: In the previous total ionic equation:  Spectator ions are nitrate ions (NO3−NO3−) and calcium ions (Ca2+Ca2+). Net Ionic Equation  Remove spectator ions from the total ionic equation to obtain the net ionic equation.  For 2Ag+(aq)+2NO3−(aq)+Ca2+(aq)+2Cl−(aq)→2AgCl(s)+Ca2+(aq)+2NO3−(aq)2A g+(aq)+2NO3−(aq)+Ca2+(aq)+2Cl−(aq)→2AgCl(s)+Ca2+(aq)+2NO3−(aq): 2Ag+(aq)+2Cl−(aq)→2AgCl(s)2Ag+(aq)+2Cl−(aq)→2AgCl(s) If possible, reduce coefficients to the simplest whole number ratio. Ag+(aq)+Cl−(aq)→AgCl(s)Ag+(aq)+Cl−(aq)→AgCl(s) 📝 Another Example: Lead Nitrate and Sodium Bromide Consider the reaction between lead nitrate (Pb(NO3)2Pb(NO3)2) and sodium bromide (NaBrNaBr). 1. Predict the products: o Lead (PbPb) pairs with bromide (BrBr) to form lead bromide (PbBr2PbBr2). o Sodium (NaNa) pairs with nitrate (NO3NO3) to form sodium nitrate (NaNO3NaNO3). 2. Determine the formulas: o Lead has a +2 charge (from the two nitrate ions). o Bromide has a -1 charge. o Using the crisscross method: PbBr2PbBr2 o Sodium has a +1 charge, and nitrate has a -1 charge. o Therefore, NaNO3NaNO3. 3. Write the unbalanced equation: Pb(NO3)2+NaBr→PbBr2+NaNO3Pb(NO3)2 +NaBr→PbBr2+NaNO3 4. Balance the equation: Pb(NO3)2+2NaBr→PbBr2+2NaNO3Pb(NO3)2 +2NaBr→PbBr2+2NaNO3  5. Determine the phases: o Nitrates are always soluble, so NaNO3NaNO3 is aqueous. o Halides are generally soluble except with silver, lead, and mercury, so PbBr2PbBr2 is insoluble (solid). o Alkali metals like sodium are always soluble. 6. Complete molecular equation: Pb(NO3)2(aq)+2NaBr(aq)→PbBr2(s)+2NaNO3(aq)Pb(NO3)2 (aq)+2NaBr(aq)→PbBr2(s)+2NaNO3(aq) 7. Write the total ionic equation: Pb2+(aq)+2NO3−(aq)+2Na+(aq)+2Br−(aq)→PbBr2(s)+2Na+(aq)+2NO3−(aq)P b2+(aq)+2NO3−(aq)+2Na+(aq)+2Br−(aq)→PbBr2(s)+2Na+(aq)+2NO3−(aq) 8. Identify spectator ions: o Sodium ions (Na+Na+) and nitrate ions (NO3−NO3−). 9. Write the net ionic equation: Pb2+(aq)+2Br−(aq)→PbBr2(s)Pb2+(aq)+2Br−(aq)→PbBr2(s) 🧪 Precipitation Reactions and Net Ionic Equations Determining Products in Precipitation Reactions  Precipitation reactions are double replacement reactions.  The first and last ions pair up, and the two middle ions pair up.  Example reaction: Silver nitrate (AgNO3AgNO3) + Calcium chloride (CaCl2CaCl2) Charges of Ions  Silver (AgAg) has a +1 charge (deduced from nitrate's -1 charge).  Nitrate (NO3NO3) has a -1 charge.  Chloride (ClCl) has a -1 charge (halogens typically have -1 charge).  Calcium (CaCa) has a +2 charge. Crisscross Method  Use the crisscross method to determine the formula of the products.  Example: Calcium (Ca2+Ca2+) and Nitrate (NO3−NO3−) combine to form Ca(NO3)2Ca(NO3)2 Balancing the Equation  Balance the equation after determining the products.  Example: 2AgNO3+CaCl2→2AgCl+Ca(NO3)22AgNO3+CaCl2 →2AgCl+Ca(NO3)2 Determining Phases   Nitrates are always soluble (aqueous phase).  Chlorides are generally soluble, except with silver (AgAg), mercury (HgHg), and lead (PbPb). Complete Molecular Equation Example 2AgNO3(aq)+CaCl2(aq)→2AgCl(s)+Ca(NO3)2(aq)2AgNO3(aq)+CaCl2 (aq)→2AgCl(s)+Ca(NO3)2(aq) Total Ionic Equation  Separate all aqueous substances into ions.  Keep solid substances as they are.  Example: 2Ag+(aq)+2NO3−(aq)+Ca2+(aq)+2Cl−(aq)→2AgCl(s)+Ca2+(aq)+2NO3−(aq)2Ag+(aq) +2NO3−(aq)+Ca2+(aq)+2Cl−(aq)→2AgCl(s)+Ca2+(aq)+2NO3−(aq) Spectator Ions Spectator ions: Ions that appear unchanged on both sides of the equation.  Spectator ions in the example: Nitrate (NO3−NO3−) and Calcium (Ca2+Ca2+) Net Ionic Equation  Remove spectator ions from the total ionic equation.  Example: Ag+(aq)+Cl−(aq)→AgCl(s)Ag+(aq)+Cl−(aq)→AgCl(s) 📝 Example 2: Lead Nitrate and Sodium Bromide Reactants  Lead nitrate (Pb(NO3)2Pb(NO3)2) and Sodium bromide (NaBrNaBr) are typically in aqueous solutions. Solubility Rules  Nitrates are always soluble.  Alkali metals (Lithium, Sodium, Potassium) are always soluble. Predicting Products  Lead (PbPb) pairs with Bromide (BrBr).  Sodium (NaNa) pairs with Nitrate (NO3NO3).  Determining Charges: o Lead (PbPb) has a +2 charge (from two nitrate ions). o Bromide (BrBr) has a -1 charge (halide). o Sodium (NaNa) has a +1 charge (alkali metal). o Nitrate (NO3NO3) has a -1 charge. Determining Formulas   Lead and Bromide: PbBr2PbBr2  Sodium and Nitrate: NaNO3NaNO3 Balanced Equation Pb(NO3)2(aq)+2NaBr(aq)→PbBr2(s)+2NaNO3(aq)Pb(NO3)2(aq)+2NaBr(aq)→PbBr2 (s)+2NaNO3(aq) Determining Phases  Nitrates are always soluble (so NaNO3NaNO3 is aqueous).  Halides are generally soluble except with silver, lead, and mercury (so PbBr2PbBr2 is insoluble/solid). Total Ionic Equation Pb2+(aq)+2NO3−(aq)+2Na+(aq)+2Br−(aq)→PbBr2(s)+2Na+(aq)+2NO3−(aq)Pb2+(aq) +2NO3−(aq)+2Na+(aq)+2Br−(aq)→PbBr2(s)+2Na+(aq)+2NO3−(aq) Identifying Spectator Ions  Sodium (Na+Na+) and Nitrate (NO3−NO3−) Net Ionic Equation Pb2+(aq)+2Br−(aq)→PbBr2(s)Pb2+(aq)+2Br−(aq)→PbBr2(s)