[Sasha]

I m also having trouble with another problem....
" A liter of sample water contains 1 mmol of calcium ions and 1.5 mmol of hydrogen carbonate ions.
how many mmol of CaCO3 will precipitate is this water is boiled for 15 min? and how many mmol of Calcium ions will remain in solution after the water has been boiled? "

Is it correct to divide the mmol of HCO3- by 2 to obtain the mmol of calcium ions. Then obtain CaCO3 mmol which is equal to the mmol of calcium ions?

and for the 2nd question.... subtract the mmol of Ca2+ (obtained in part1) from the original 1 mmol of Ca2+?

thanking you in advance 

[Borek]

Start with balanced reaction equations.