Displacement/ Replacement Reactions

What is Single Replacement?  When one element replaces another element in a compound, a single replacement (also known as displacement) reaction has taken place. Ex. Cl 2 + 2NaBr  2NaCl + Br 2

Activity Series  A single replacement reaction will only take place if a more reactive metal or halogen is replacing a less reactive one.  In order to know if one element is more reactive than another, we must look at an activity series chart  An activity series is a ranking of relative reactivity of metals and halogens in displacement reactions. The most reactive elements are at the top of the activity series, and as you go down the chart the elements become less reactive.

Single Replacement Reversibility  Just because a formula is written doesn't necessarily mean the reaction can take place. Single Replacement reactions can not be reversed.  Ex.  Cl 2 + 2NaBr --> 2NaCl + Br 2 will happen  2NaCl + Br 2 --> Cl 2 + 2NaBr will not happen **Chlorine is stronger than bromine**

Activity Series Practice  Determine IF the following reactions will take place (YES/NO) 1. K + H 2 O YES 2. Cu + H 2 SO 4 NO 3. FeCl 2 + Zn YES 4. Copper (II) sulfate + chromium YES 5. Magnesium + water NO 6. Lead (II) chloride + fluorine YES

Predicting Products of a Single Displacement Reaction  If the reaction takes place, one of three scenarios take place  1. a halogen (group 17) replaces another halogen  2. a metal replace another metal  3. a metal replaces hydrogen (in an acid or water)  An acid is just an ionic compound with hydrogen (Ex. H 2 SO 4 )  When a metal replaces hydrogen in water, you need to think of water as “hydrogen hydroxide, H+ OH - ”

Predicting Halogen Replacement Predicting from names :  When a halogen replaces another halogen, the names just switch places on the right side  Ex. sodium brom ide + chlor ine  sodium chlor ide + brom ine  Don’t confuse –ide (in a compound) with –ine (pure element) Predicting from formulas :  Both sides will not have the same number of atoms until balanced since pure halogens are diatomic  To not confuse yourself, you can convert formula to name before figuring out the right side  Ex. NaBr + Cl 2  NaCl + Br 2 (NOT: NaCl 2 + Br) Practice: 1. magnesium chloride + fluorine  2. KI + F 2  (answer is NOT KF 2 + I) (HINT: If it helps, find the answer in words then convert to formula)

Predicting Metal/Metal Replacement Predicting from names :  Again, the names just switch places and you don’t have to worry about suffixes  Ex. calcium chlorate + sodium  sodium chlorate + calcium Predicting from formulas :  Both sides will not necessarily have the same number of atoms until balanced because metals with different charges will combine in a different ratio  To not confuse yourself, you can convert formula to name before figuring out the right side  Ex. Ca(ClO 3 ) 2 + Na  NaClO 3 + Ca (Ca 2+ vs. Na + ) Practice: 1. Chromium (III)phosphate + zinc  2. Al(SO 4 ) 3 + Fe(II)  (HINT: If it helps, find the answer in words then convert to formula)

Predicting metals replacing hydrogen Predicting from names :  Again, the names just switch places  If the hydrogen is in water, think of water as hydrogen hydroxide  Ex 1. barium + water  barium hydroxide + hydrogen  Ex 2. aluminum + hydrogen sulfate  aluminum sulfate + hydrogen Predicting from formulas :  Both sides will not necessarily have the same number of atoms until balanced because metals with different charges will combine in a different ratio  To not confuse yourself, you can convert formula to name before figuring out the right side  Ex 1. Ba + H 2 O  Ba(OH) 2 + H 2 (Ba 2+ vs. H + )  Ex 2. Al + H 2 SO 4  Al 2 (SO 4 ) 3 + H 2 (Al 3+ vs. H + ) Practice: 1. Potassium + water  2. Zn + HCl 

Double Displacement/Replacement Reactions  Occurs by mixing together two aqueous solutions  2 types: 1. precipitation reaction  forming a solid from 2 solutions 2. acid/base neutralization reaction  forming H 2 O from an acidic and a basic solution

Precipitation Reactions  A solid ionic precipitate (salt) is formed from two ionic aqueous solutions  When predicting the products in the reaction, the ions switch places Ex. silver nitrate + sodium chloride  silver chloride + sodium nitrate Ex. AgNO 3 + NaCl  AgCl + NaNO 3  A reaction will only happen if one of the products are insoluble in water  Solubility is determined by referencing the products on a solubility chart  The insoluble product will say either A, P or I on the chart  If none of the products say either A, P or I on the chart, there is NO REACTION,  the new solution created is just a homogenous mixture of the reactants Practice: Which product is the precipitate in the example reaction above?

Neutralization Reaction  Water is formed from an acid and a base  Acids contain H+  Bases contain OH- Ex. hydrogen chloride + sodium hydroxide  sodium chloride + hydrogen hydroxide (water) Ex. HCl + NaOH  NaCl + HOH (H 2 O)  Acids and bases always cancel each other out so there will always be a reaction taking place