Chemicals in Solution - Background Example
You are given three vials containing solutions of lead nitrate, nitric acid and lithium carbonate. In order to systematically examine the reactions of these solutions with each other we could set up a data table like the one below.
|
| Pb(NO3)2
| HNO3
| Li2CO3
|
| Pb(NO3)2
| a
| b
| c
|
| HNO3
| d
| e
| f
|
| Li2CO3
| g
| h
| i
|
The letter "b" would be replaced with the observations you made when HNO3 and Pb(NO3)2 were mixed. The letter "c" would be replaced with the observations you made when Li2CO3 and Pb(NO3)2 were mixed, and so on. When the experiment is performed we collect the following data:
|
| Pb(NO3)2
| HNO3
| Li2CO3
|
| Pb(NO3)2
| -
| no reaction
| white precipitate
|
| HNO3
| no reaction
| -
| bubbles
|
| Li2CO3
| white precipitate
| bubbles
| -
|
Using our knowledge of chemistry, we should be able to explain these observations. The white precipitate (ppt) is the result of a double displacement reaction which forms an insoluble product (insoluble products can be identified using a table of solubility rules).
Pb(NO3)2 + Li2CO3 
PbCO3(solid) + 2 LiNO3
The bubbles are the result of a double displacement reaction in which an unstable product is formed. This unstable product then decomposes to form a gas.
2 HNO3 + Li2CO3 H2CO3(unstable) + 2 LiNO3
H2CO3 H2O + CO2(gas)
Further suppose that you are now given some unknowns.
