4.2 Double Displacement Reactions Flashcards
Double displacement reactions (also called double replacement, exchange, metathesis reactions)
* What are the 3 major types?
1) Parcipitation reactinos
2) Acid base neutralization reactions
3) Gas forming
Double displacement reactions: basically the cations and the anions just switch places (cation typically written first and that reflects this)
AB + CD –> AD + CB
If we form a solid = parcipitation reaction
If your reactants are acids and bases = acid base neutralization reaction
One special case that results in the production of a gas = gas forming double replacement rxn
Double displacement rxn: Parcipitation rxn
* again, the hallmark of this is that we end up forming a solid
Pb(NO3)2 (aq) + NaI (aq) –>
* We often have to predict products
* So essentially you’re just taking the cation of one and combining it w/ the anion of the other
* remember, cations go first
Pb(NO3)2 (aq) + NaI (aq) –> PbI + N(NO3)2
* however, this is incorrect, to predict the proper formula you need to know the charges
The key here is that you carry the original chrages from the left side and then balance the ionic compounds w/ those charges
This is shown more clearly on the following slide
This is a parcipitation double displacement rxn
So in the ionic equation you can see two of the ions actually combined and the other 2 didnt, they are soluble, so they disassociated. These are called spectator ions
Net Ionic equation is written w/o the spectator ions
next slide has this fully worked, and the picture below is the last thing you do
* essentially this is eliminating everyone that didnt do anything
2nd Type of double displacement reaction = Acid base Neutralization - shown w/ a strong acid and a strong base
* remember, they’re switching partners because this is a double displacement reaction
base is always a hydroxide base
spectators ions = part of a strong electrolyte on both sides of the equation
* Exist in a fully disassociated state on both sides of the reaction
Salt doesnt have to be NaCl
* A salt is any ionic compound
When you do any acid base neutralization you’re typically going to get H2O and a salt (ionic compound) –> like shown in the equation below
Double displacement reaction
* Acid base neutralization
* **Shown w/ a weak acid and a strong base
HF
* can identify as an acid because it starts w/ an H. However, its not one of our 8 strong acids (need these memorized)
* This is not going to dissaociate fully as a strong electrolyte would, which will change some thing when identifying spectator ions and writing our net ionic equation
NaOH
* This is a strong base - meaning it dissasociates fully into electrolytes in H2O
NaF = aq - all group 1 salts (ionic compounds) are soluble - This wasnt one of our solubility rules
Theres a big difference between 3Na and Na3
3Na = 3 separate atoms of sodium
Na3 = Siggests a compound or cluster containing three sodium atoms bonded or grouped together
* typically in part of a chemical formula like Na3PO4
This is showing how to balance an annoying equation
* don’t balance writing H2O –> leave it has HOH
3rd kind of double displacement rxn: Gas-Forming
Big thing to know is that H2CO3 (carbonic acid) when formed cannot be the final product because it immediately disassociates into H2O and CO2 (g), which are the final products instead
* this is the steaming you’ll see at the top of volcanos in science fairs
This is likely the only gas forming double displacement rxns I’ll have to know
* However, other gas forming rxns do happen, they just arent double displacement rxns
1 and 2
Keys is to know strong acids and bases
as a double displacement
The way you know you’re doing a double dispalcement problem is that you have two ionic compounds in solution
So it was just balancing it. Not going into ionic formula
Key is to first notice its a double displacement rxn
* This is because its two ionic compounds / acids / bases
NOTE: strong acids / strong bases are considered strong electrolytes because they dissassociate completely into ions = high concentration of ions = strong electroltes - this allows them to conduct electricity very well
A strong electrolyte is any compound that, when dissolved in water, produces a alrge number of ions that can move freely, allowing the solution to conduct electrical current efficiently
*
Spectator ion = part of a strong electrolyte on each side of the rxn arrow
KNOW: adding onto solubility rules that all group 1 Salts are soluble (meaning that if a group 1 metal is in the salt name its considered a strong electrolyte = fully soluble)
KNOW: adding onto solubility rules that all group 1 Salts are soluble (meaning that if a group 1 metal is in the salt name its considered a strong electrolyte = fully soluble)
1 and 2
A gas can dissolve in liquids, however, at higher temps they are less soluble
Pressure will impact it –> if i increase pressure it will force more of that gas into the liquid phase
