Consider the following equilibrium:
CaCO3(s)<->Ca 2+(aq) + CO3 2-(aq)
Which of the following reagents, when added to the equilibrium system, would cause more CaCO3 to dissolve?
a)KNO3(s), can't be this, NO3 is soluble with all negative ions
b)CaCO3(s), adding more CaCO3 won't cause it to dissolve more
c)H2C2O4(s)
d)Na2CO3(s)
The answer is not d because it will make more CaCO3(s)? So the answer is c.
c is the correct answer. H2C2O4 is oxalic acid and although it is a weak acid (both k1 and k2 are small) it does increase the H^+ concn in the solution and that will dissolve more CaCO3 just as any acid will. Technically, KNO3 will make it more soluble also because it will increase the ionic strength of the solution; however, I doubt that you have talked about that yet and I wouldn't pick that over c anyway. But if you will take more chemistry, file that somewhere in the back of your brain and remember it down the road.
Thanks! I'll keep that in mind.
Yes, you are correct. Adding Na2CO3(s) would cause more CaCO3 to precipitate, not dissolve. Therefore, the correct answer is c) H2C2O4(s).
To determine which of the given reagents would cause more CaCO3 to dissolve in the equilibrium system, we need to consider the Le Chatelier's principle. This principle states that if a stress is applied to a system at equilibrium, the system will respond in a way that reduces the effect of that stress.
In this case, we want to find a reagent that will cause more CaCO3 to dissolve. This means that we need to shift the equilibrium to the right, favoring the formation of Ca2+(aq) and CO3 2-(aq) ions.
Let's analyze the options:
a) KNO3(s): The addition of KNO3 would provide NO3- ions, which are soluble and do not interact with CaCO3 to promote dissolution. Therefore, it will not cause more CaCO3 to dissolve.
b) CaCO3(s): Adding more CaCO3 to the system will not cause the existing CaCO3 to dissolve more. It will simply increase the solid concentration, without affecting the dissolution equilibrium.
c) H2C2O4(s): The addition of H2C2O4 (oxalic acid) would provide C2O4 2- ions. These ions can react with Ca2+ to form a sparingly soluble CaC2O4 precipitate. This reaction removes Ca2+ ions from the solution, shifting the equilibrium to the right and increasing the dissolution of CaCO3. Therefore, this reagent would cause more CaCO3 to dissolve.
d) Na2CO3(s): Adding Na2CO3 would provide CO3 2- ions. These ions can react with Ca2+ to form a precipitate of CaCO3, which would decrease the amount of dissolved CaCO3. So, this reagent would not cause more CaCO3 to dissolve.
Based on this analysis, the correct answer is c) H2C2O4(s). By adding oxalic acid to the equilibrium system, it provides C2O4 2- ions that can react with Ca2+ ions to form a precipitate, thus causing more CaCO3 to dissolve.