Complete and balance the following molecular equations/write balanced ionic equation/write net ionic equation?

Question

Pb(NO3)2 (aq) + Na3PO4 (aq)

and

HCl (aq) + Sr(OH)2 (aq)

Answer 1

You have Pb2+ and PO4 3-; so the insoluble lead phosphate is Pb3(PO4)2 (make sure you understand why this is).

If this is one of your products, that will tell you how many Pb(NO3)2 (aq) and Na3PO4 (aq) you need it in your reagents for balance.  You can then see what is left over in solution.

Then write out that the same equation, but replace every salt in the solution by its ions; e.g. Na3PO4(aq) becomes 3Na+(aq) + PO4 3-(aq). That is your balanced ionic equation.

Finally, cross out all the ions (such as, in this case, Na+) which are present in the same numbers on both sides of the equation.  These are what are called spectator ions, and at the ionic level were not really involved in the reaction.

Second example: strong acid and strong base.  You need equal numbers of H+(aq) and OH- (aq), and they react to make H2O (l for liquid).  

Hope this helps. Over to you

Answer 2

3Pb(NO3)2 (aq)+2 Na3PO4 (aq)>> Pb3(PO4)2 (s) + 6 NaNO3 (aq)

3 Pb2+ + 6 NO3- + 6 Na+ + 2 PO43- >> Pb3(PO4)2 + 6 Na+ + 6 NO3-

cancel any duplications to get the net ionic :

3 Pb2+ + 2 PO43- >> Pb3(PO4)2

2 HCl (aq)+ Sr(OH)2 (aq)>> SrCl2 (aq)+ 2 H2O (l)

2 H+ + 2 Cl- + Sr2+ + 2 OH- >> Sr2+  + 2Cl- + 2 H2O

2H+ + 2 OH- >> 2 H2O