Which is used to convert between mass and moles of a substance?

About 3% of the water on earth is freshest. only about 40% of that freshwater is available for human use. why is so much freshwater unavailable for human use?

Which is the solubility product expression for caf2(s)?  [ca2+]/[f–]2  [ca2+][f2–]  [ca]+[f]2  [ca2+][f–]2

What information does a complete ionic equation give that the balanced equation doesn’t show?