Consider the following system at equilibrium.

CaCO3(s) mc032-1.jpg Ca2+(aq) + CO32–(aq)

The addition of which compound will cause a shift in equilibrium because of a common ion effect?

CCl4

CO2

CuSO4

Na2CO3

2 answers

Na2CO3 => 2(Na^+) + 1(CO3^-2)

The CO3^-2 is the common ion and addition of more CO3^-2 will overload the PRODUCT side causing the equilibrium to shift left to remove the excess and re-establish a new equilibrium.
yup