PLEASE HELP 6.203g of Na2CO3.xh2o was dissolved in water and the solution made up of 1000cm3. If 25cm3 of this solution requires 20.5cm3 of 0.122moldm-3 hydrochloric acid for complete neutralisation, calculate the mass of the hydrated salt​

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)

the answer is c.the valence of the atoms combine .