Asample containing 0.213g cl- is dissolved in 50.0ml of water how many moles of cl- are in the solution?

There are 0.006 moles of Cl- in the solution.

Explanation:

To solve this problem you should think in te concept of molar mass, the molar mass of Cl- is 35.45 grs/mol (it has the same mass as Cl, because electrons doesn´t contribute with significant mass). So,

35.45 grs 1 mol Cl-

0.213 grs   x = 0.006 moles Cl-

There are 0.006 moles of Cl- in the solution.

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.