Question

____ moles of Ba was added and _____ moles of precipitate of BaCO3 was recovered. The mole ratio of cation to precipitate is _____.
how do i do this?

Answer 1

Because of where it sits on the Periodic Table, barium will lose 2 electrons to become stable and "look like" xenon. This creates the +2 ion that all Group 2 metals form (that's why it's periodic). The carbonate ion has a -2 charge (one of those ions you probably just have to memorize). This creates a 1:1 ratio in the formula BaCO3 in order to make a neutral compound. Since 1 atom of barium will form 1ion of barium, and 1 ion of barium will form 1 ionic crystal of BaCO3, then the mole ratio of barium atoms to barium carbonate is also 1:1, so your final answer is the ratio 1:1.