Chem 106 LB
November 15th, 2012
Summary – Precipitating in Central Park
Warm-Up Exercise 1
We have 3 equations: complete chemical equation, complete ionic equation and net ionic equation. The difference between them is that a complete ionic equation shows all the ions that are floating around in the reaction mixture. The Net ionic equation only shows the ions that are participating in the reaction. The spectator ions are left out.
For reaction (II)
Pb (NO3)2 + 2KI -> PbI2+2KNO3
Lead nitrate is soluble, so it gets written as ions. The same goes for potassium iodide and potassium nitrate.
Complete Ionic equation:
2 K+1 + I-1 + Pb2+ + NO32- -> PbI2 + 2K+1 + NO3-1
Net Ionic Equation:
Pb+2 + 2 I-1 -> PbI2
Warm-Up Exercise 2
In this lab you will mix 25 mL of 0.05M lead nitrate with 1.4 mL of 0.025M sodium carbonate. After the reaction occurs, you will filter the solution to remove the precipitate. You will then test the remaining solution for excess lead ion and for excess carbonate ion…
Imagine that you mix the two volumes and then freeze frame the reaction so the it does not proceed:
1. Identify all the ionic species present in the solution before the reaction takes place.
2. Compute the molarity and the number of moles of each ionic species present before the reaction takes place.
After reaction goes to completion:
3. Identify all the ionic species present in solution
4. Compute the molarity and the number of moles of each ionic species present.
5. Clearly predict the results of the experiment by determing which reactant is limiting and which is in excess.
Pb(NO3)2(aq) + Na2CO3(aq) --> PbCO3(s) + 2NaNO3(aq)
1)Before Pb+2(aq) + NO3(aq)- + Na+(aq) + CO3-2(aq)
25 ml of 0.05 mole Pb(NO3)2/1000ml = 0.00125 moles Pb(NO3)2(aq)
Pb(NO3)2(aq) --> Pb+2(aq) + 2NO3-(aq)
0.00250 moles of NO3-(aq)
and 0.00125 moles of Pb+2(aq)
1.4 ml * 0.025 mole Na2CO3/1000ml = 0.000035 moles Na2CO3(aq)...