Displacement Reactions

+ + Single Displacement Reactions Single Displacement reaction: A chemical reaction in which an element takes the place of (displaces) another element in a compound A + BC AC + B (where A & B are metals) A + BC BA + C (where A & C are non-metals) + +

Displacing Metals With Metals When a piece of copper is placed into silver nitrate, metallic silver ions form on the copper The solution turns blue because copper atoms from the wire dissolve in solution and displaces the silver from the silver nitrate compound Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)

Displacing Metals With Metals In this reaction a metal (copper) replaces another metal (silver) Or, a positive ion (Cu2+) replaced another positive ion (Ag3+) Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)

The Activity Series By trying different combinations of metals and compounds, scientists have arranged the metals according to their reactivity The activity series is a list of elements ranked according to their chemical reactivity Most reactive is at the top, least at the bottom An element can only displace another if it is below it on the activity series!!

The Activity Series Hydrogen is the only non-metal in the series Since hydrogen ions can be positively charged, metals can replace hydrogen in compounds In these reactions, hydrogen gas H2(g) is formed Metals above hydrogen can replace hydrogen from an acid, metals below hydrogen cannot What do you get when you place Zn in HCl?

The Activity Series An example of Zinc (Zn) displacing hydrogen gas from hydrochloric acid (HCl) Zn(s) + 2HCl (aq) ZnCl2(aq) + H2(g)

Sample Problem: The Activity Series Use the activity series to predict if the following reaction will occur. If not, indicate “NR” for “No Reaction”. If so, complete and balance the chemical equation Al(s) + CuI2(aq)

Sample Problem: The Activity Series Aluminum will replace copper Aluminum becomes Al3+ and the bromide ion remains Br- To be neutral, the new compound must be CuBr2 As a pure element Cu(s) has no charge The skeleton equation is the same as the balanced equation Al(s) + CuBr2(aq) Cu (s) + AlBr2 (aq)

Replacing Non-metals with Non-metals The ion of a non-metal (Cl-) is negatively charged so it can only be replaced with another non-metal F2(g) + 2NaI(s) I2(s) + 2NaF(s)

+ + Double Displacement Reactions Double Displacement reaction: A chemical reaction in which the positive ions of two compounds change places and form two new compounds Double Displacement reactions often result in the product of an insoluble solid or precipitate AB + CD AD + CB (A & C are cations and B and D are anions) + +

Double Displacement Reactions Example: when a yellow aqueous solution of potassium chromate is added to a colorless aqueous solution of silver nitrate a red precipitate of silver chromate is formed: 2AgNO3(aq) + K2CrO4(aq) Ag2CrO4(s) + 2KNO3(aq)

Double Displacement Reactions Complete and balance the following double displacement reaction. You do not need to predict the states of the products NaCl(aq) + AgNO3(aq)

Double Displacement Reactions Solution: NaCl(aq) + AgNO3(aq) This is a double displacement reaction so the two cations must switch Sodium and silver will therefore switch – both have a 1+ charge so the ratio to anions does not change The skeleton equation is the same as the balanced equation for this reaction NaCl(aq) + AgNO3(aq) AgCl + NaNO3

Summary of Chemical Reactions Reaction Type Chemical Equation Example Characteristics Synthesis A + B AB 2H2(g) + O2(g) 2H2O(g) Two reactants join forming a single compound Decomposition AB A + B 2C7H5N3O6(s ) 3N2(g) + 5H2O (g) + 7CO (g) + 7C(s) A single compound breaks apart making two or more products Single Displacement A + BC AC + B A + BC BA + C 2Al(s) + 3CuCl2(aq) 2AlCl3(aq) + 3Cu(s) A reactive element takes the place of a less reactive element Double Displacement AB + CD AD + BC NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq) Two ionic compounds switch ions to form new compounds & a ppt