Experiment

Na2C2O4 is added to Pb(NO3)2.Precipitate forms (I think its PbC2O4). After the liquid above was decanted to another container. Dilute HNO3(aq) was added to it. The decanted cloudy solution cleared up a little but it was kinda cloudy still.

Im not sure how PbC2O4(s) <-->Pb^2+ + C2O4^2- equilibrium will react with dilute HNO3(aq).Can someone explain what's happening? What equilibrium is being disturbed?

It isn't clear from your description of HNO3 was added to the decantate or to the ppt. I assume to the ppt.

Pb(C2O4)(s) ==>Pb^2+(aq) + C2O4^2-(aq)
HNO3 dissolves the ppt because it forms H2C2O4 (oxalic acid).

It was added to the decantate.

I can't figure out why anything was added to the decantate; it contains only NaNO3 plus whatever small amount of PbC2O4 that was allowed to spill over. So adding HNO3 will dissolve any of the small particles of H2C2O4.

In this experiment, you added sodium oxalate (Na2C2O4) to lead nitrate (Pb(NO3)2), resulting in the formation of a precipitate, which you correctly identified as lead oxalate (PbC2O4). The equation for this reaction can be represented as follows:

Na2C2O4(aq) + Pb(NO3)2(aq) → PbC2O4(s) + 2NaNO3(aq)

As you mentioned, the liquid above the precipitate was decanted into another container. Now, when you added dilute nitric acid (HNO3(aq)) to this decanted solution, the cloudy solution cleared up a little but remained somewhat cloudy. Let's explore what is happening during this step.

When you add dilute nitric acid (HNO3(aq)) to the solution containing the lead oxalate precipitate, an acid-base reaction occurs. Nitric acid is a strong acid, which dissociates completely in water to release hydrogen ions (H+). The equation for this reaction is:

HNO3(aq) → H+(aq) + NO3^-(aq)

The hydrogen ions (H+) from the nitric acid react with the anions (C2O4^2-) produced by the dissolution of lead oxalate. The equation for this reaction can be represented as follows:

H+(aq) + C2O4^2-(aq) → H2C2O4(aq)

In this reaction, the hydrogen ions react with oxalate ions to form oxalic acid (H2C2O4). This reaction disturbs the equilibrium between the lead oxalate (PbC2O4) and the ions (Pb^2+ and C2O4^2-) in solution.

The disturbance of the equilibrium causes the lead oxalate precipitate to dissolve partially, resulting in the clearing up of the solution. However, some lead oxalate may still remain undissolved, which is why the solution remains somewhat cloudy.

It's also worth noting that the nitrate ions (NO3^-) from the nitric acid do not play a significant role in this reaction. They remain in solution as spectator ions.

In summary, the addition of dilute nitric acid to the solution disturbs the equilibrium between the lead oxalate precipitate and its ions. This disturbance causes the lead oxalate to partially dissolve, resulting in the clearing up of the solution. However, some lead oxalate may still remain undissolved, leading to a cloudy appearance.