Net Ionic Equations

mixing ionic compoundsmixing ionic compounds

Ionic interactions

When you dissolve 2 or more ionic When you dissolve 2 or more ionic compounds in water some parts of it may compounds in water some parts of it may react together and precipitate outreact together and precipitate out

Precipitate-solid falling out of solutionPrecipitate-solid falling out of solution More times than not, most (if not all) of the More times than not, most (if not all) of the

ions do nothingions do nothing Net ionic equations are only concerned with Net ionic equations are only concerned with

the ions that do somethingthe ions that do something

This goes back to ionic dissociation in waterNaCl(s) + AgNO3(s) in water

Na+(aq)

+ Cl-(aq) + Ag+

(aq) + NO3-(aq)

Here’s the trick, AgCl is insoluble

AgCl(s) + Na+(aq) + NO3

-(aq)

Net ionic ignoreseverything thatdoesn’t do anything!

Ag+(aq) + Cl-

(aq) AgCl(s) net ionic equation--

More net ionic equations You normally write the reactants as aqueous You normally write the reactants as aqueous

(since you are dissolving them)(since you are dissolving them) Mg(NOMg(NO33))2(aq)2(aq) + Na + Na22COCO3(aq)3(aq) MgCO MgCO3(s) 3(s) + 2NaNO+ 2NaNO3(aq)3(aq)

Dissociate everything that is aqueous, not solidDissociate everything that is aqueous, not solid MgMg++ ++ + 2NO+ 2NO33

-- + 2Na + 2Na++ + CO + CO33----

MgCOMgCO3(s) 3(s) + 2 Na+ 2 Na+ + + 2NO+ 2NO33--

Now cancel out everything that is the same on Now cancel out everything that is the same on both sides of the equationboth sides of the equation

These are called These are called spectator ionsspectator ionsThe remainingpart is the netionic equationMgMg++ ++ + CO+ CO33

-- -- MgCO MgCO3(s)3(s)

What if nothing precipitates out?

KK22SOSO4(aq)4(aq)+AgNO+AgNO3(aq)3(aq) KNO KNO3(aq) 3(aq) + Ag+ Ag22SOSO4(aq)4(aq)

(by the way, this equation isn’t balanced)(by the way, this equation isn’t balanced) 2 K2 K++ + SO + SO44

2-2- + Ag + Ag++ + NO + NO33--

KK++ + NO + NO33-- + 2 Ag + 2 Ag++ + SO + SO44

2-2-

Everything cancels outEverything cancels out There is no net ionic equationThere is no net ionic equation

Practice with equations that are not yet balanced

KK22COCO3(aq)3(aq)+ Ca(NO+ Ca(NO33))2(2(aq)aq) KNOKNO3(aq) 3(aq) + CaCO+ CaCO3(s)3(s)

2K2K++ + CO + CO332-2- + Ca + Ca++++ + 2 NO + 2 NO33

--

CaCOCaCO3(s) 3(s) ++ KK++ + NO + NO33

--

Just ignore coefficients when cancelingJust ignore coefficients when canceling CaCa++ ++ + + COCO33

2-2- CaCOCaCO3(s) 3(s)

If it were unbalanced now you would If it were unbalanced now you would balance itbalance it

Tip to make sure your answer is right Make sure you have the same atoms on Make sure you have the same atoms on

each side of the equationeach side of the equation If your final answer is something likeIf your final answer is something like KK+ + + + COCO33

2-2- CaCOCaCO3(s)3(s)

It is wrong!!!It is wrong!!! Atoms don’t spontaneously change into Atoms don’t spontaneously change into

other atoms (without a nuclear reaction)other atoms (without a nuclear reaction)

Homework

NaNa33POPO4 (aq) 4 (aq) + Ba(NO+ Ba(NO33))2 (aq) 2 (aq)

NaNONaNO3 (aq) 3 (aq) + Ba+ Ba33(PO(PO44))2 (s) 2 (s)