4.3 Single Displacement and Double Displacement Reactions SCH3U Ms. Munir

Single Displacement Reactions In a single displacement reaction, one element in a compound is displaced (or replaced) by another element. There are 2 different types of SD reactions. One type involves a metal replacing a metal cation in a compound. A + BC → AC + B Zn(s) + Fe(NO3)2(aq) → Zn(NO3)2(aq) + Fe(s) The second type of SD reaction involves a non-metal (usually a halogen) replacing an anion in a compound. DE + F → DF + E Cl2(g) + CaBr2(aq) → CaCl2(aq) + Br2(g)

Single Displacement Reactions and the Metal Activity Series Most single displacement reactions involve one metal displacing another metal from a compound. Mg(s) + ZnCl2(aq) → MgCl2(aq) + Zn(s) Treat hydrogen as a metal. Treat acids, such as HCl, as ionic compounds of the form H+Cl−. Treat water as ionic, with the formula H+(OH−).

Metal Activity Series

Predicting SD Products If the metal displacing a cation is higher in the series, reaction will take place. Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) If the metal displacing a cation is lower in the series, no reaction will take place. Ag(s) + CaCl2(aq) → N.R.

Single Displacement Reactions Involving Halogens The activity series for halogens directly mirrors the position of halogens in the periodic table. F>Cl>Br>I Cl2(g) + 2KBr(aq) → 2KCl(aq) + Br2(l) I2(aq) + CaBr2(aq) → NR

Double Displacement Reactions A double displacement reaction involves the exchange of cations between two ionic compounds, usually in aqueous (water) solution. A DD reaction is also known as a double replacement reaction. AB + CD → CB + AD NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq)

Continued… DD reaction takes place when: a solid (precipitate) forms a gas is produced some DD reactions also form a molecular compound, such as water. It is hard to tell when water is formed, because often the reaction takes place in water.

Double Displacement Reactions that Form a Precipitate A precipitate is a solid that separates from a solution as the result of a chemical reaction. BaCl2(aq) + K2SO4(aq) → BaSO4(s) + 2KCl(aq)

Think about this… How do we determine the products? Deconstruct and reconstruct the equation Which of the products—if any—will precipitate out of solution? Learn solubility chart [later in the course]

Double Displacement Reactions That Produce a Gas The gas is formed when one of the products of the double displacement reaction decomposes to give water and a gas. Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2CO3(aq) H2CO3(aq) → H2O(l) + CO2(g) Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)

The Formation of Water in Neutralization Neutralization reactions are a special type of DD reaction that produces water. Neutralization involves the reaction of an acid with a base to form water and an ionic compound (salt). HNO3(aq) + NaOH(aq) → NaNO3(aq) + H2O(l) P 140 -141 #1 – 6 McGrawHill P 169 # 1 – 9 Nelson P 177 #1 – 7 Nelson