Displacement Reactions Single Displacement Reactions Single Displacement reaction

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 • A + BC BA + C (where A & C are non-metals) + (where A & B are 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) + 2 Ag. NO 3(aq) Cu(NO 3)2(aq) + 2 Ag(s)

Displacing Metals With Metals • In this reaction a metal (copper) replaces another metal (silver) • Or, a positive ion (Cu 2+) replaced another positive ion (Ag 3+) Cu(s) + 2 Ag. NO 3(aq) Cu(NO 3)2(aq) + 2 Ag(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 H 2(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) + 2 HCl (aq) Zn. Cl 2(aq) + H 2(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) + Cu. I 2(aq)

Sample Problem: The Activity Series • Aluminum will replace copper • Aluminum becomes Al 3+ and the bromide ion remains Br • To be neutral, the new compound must be Cu. Br 2 • As a pure element Cu(s) has no charge • The skeleton equation is the same as the balanced equation Al(s) + Cu. Br 2(aq) Cu (s) + Al. Br 2 (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 F 2(g) + 2 Na. I(s) I 2(s) + 2 Na. F(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: 2 Ag. NO 3(aq) + K 2 Cr. O 4(aq) Ag 2 Cr. O 4(s) + 2 KNO 3(aq)

Double Displacement Reactions • Complete and balance the following double displacement reaction. You do not need to predict the states of the products Na. Cl(aq) + Ag. NO 3(aq)

Double Displacement Reactions Solution: Na. Cl(aq) + Ag. NO 3(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 Na. Cl(aq) + Ag. NO 3(aq) Ag. Cl + Na. NO 3

Summary of Chemical Reactions Reaction Type Chemical Equation Example Characteristics Synthesis A + B 2 H 2(g) + O 2(g) 2 H 2 O(g) Two reactants join forming a single compound Decomposition AB 2 C 7 H 5 N 3 O 6(s ) 3 N 2(g) + 5 H 2 O (g) + 7 C(s) A single compound breaks apart making two or more products Single Displacement A + BC 2 Al(s) + 3 Cu. Cl 2(aq) 2 Al. Cl 3(aq) + 3 Cu(s) A reactive element takes the place of a less reactive element Double Displacement AB + CD Na. Cl(aq) + Ag. NO 3(aq) Ag. Cl(s) + Na. NO 3(aq) Two ionic compounds switch ions to form new compounds & a ppt A + BC AB A + B AC + B BA + C AD + BC