Question 3.3.2: Balance equations. Balance the chemical equation for the neu......
Balance equations.
Balance the chemical equation for the neutralization of phosphoric acid by calcium hydroxide to form calcium phosphate and water. The unbalanced equation is
H_{3}PO_{4} + Ca(OH)_{2} → Ca_{3}(PO_{4})_{2} + H_{2}O.
You are asked to balance a chemical equation.
You are given an unbalanced equation.
Notice that both hydrogen and oxygen appear in more than one compound in the reactants. Begin by balancing the other elements, phosphorus and calcium, before balancing hydrogen and oxygen.
H_{3}PO_{4} + Ca(OH)_{2} → Ca_{3}(PO_{4})_{2} + H_{2}O.
\, 5 H 2 H
\, 1 P 2 P
\, 6 O 9 O
\, 1 Ca 3 Ca
Balance phosphorus. Change the coefficient in front of H_{3}PO_{4} from 1 to 2 and note the change in H and O.
2 H_{3}PO_{4} + Ca(OH)_{2} → Ca_{3}(PO_{4})_{2} + H_{2}O.
\, 8 H 2 H
\, 2 P 2 P
\, 10 O 9 O
\, 1 Ca 3 Ca
Balance calcium. Change the coefficient in front of Ca(OH)_{2} from 1 to 3 and note the change in H and O.
2H_{3}PO_{4} + 3Ca(OH)_{2} → Ca_{3}(PO_{4})_{2} + H_{2}O.
\, 12 H 2 H
\, 2 P 2 P
\, 14 O 9 O
\, 3 Ca 3 Ca
Balance hydrogen and oxygen. Changing the coefficient in front of H_{2}O from 1 to 6 (each increase in the H_{2}O coefficient adds two H atoms) balances both hydrogen and oxygen.
2 H_{3}PO_{4} + 3 Ca(OH)_{2} → Ca_{3}(PO_{4})_{2} + 6 H_{2}O
\, 12 H 12 H
\, 2 P 2 P
\, 14 O 14 O
\, 3 Ca 3 Ca
The equation is balanced.
Is your answer reasonable? When balancing equations, it is a good idea to check the atom balance for all elements in the equation when you are finished. In this case, there are equal numbers of elements in both reactants and products, so the equation is balanced.