13.
balance the equation.
ca(no3)2 + na2co, → caco3 + na no3

Ca(NO3)2 + Na2CO3 -> CaCO3 + 2NaNO3

Explanation:

As Calcium ion (Ca) has a valency of +2, it requires an anion with equivalent valency of -2. Nitrate ion (NO3) has a valency of -1 so it needs 2 molecules of it to satisfy the Calcium's +2 valency.

Carbonate (CO3) has -2 valency, so it replaces the 2 NO3 molecules by 1 of itself and bonds to Ca.

Sodium (Na) has +1 valency, so it is satisfied by 1 molecule of NO3 but there are 2 molecules of both Na and NO3. Therefore, we attach the stoichiometric coefficient of 2 to NaNO3.

explanation:

two years ago, when picking flowers in the mountains back of yosemite valley, i found a book. it was blotted and storm-beaten; all of its outer pages were mealy and crumbly. the paper seemed to dissolve like the snow beneath which it had been buried, however; many of the inner pages were well preserved. and although all were more or less stained and torn, whole chapters were easily readable. this is the condition of the great open book of yosemite glaciers today; its granite pages have been torn and blurred by the same storms that wasted the castaway book.

two years ago, when picking flowers in the mountains back of yosemite valley; i found a book. it was blotted and storm-beaten, all of its outer pages were mealy and crumbly. the paper seemed to dissolve like the snow beneath which it had been buried, however, many of the inner pages were well preserved. and although all were more or less stained and torn; whole chapters were easily readable. this is the condition of the great open book of yosemite glaciers today, its granite pages have been torn and blurred by the same storms that wasted the castaway book.