E Balancing Chemical Equations

Sample Problem E Aluminum sulfate and calcium hydroxide are used in a water-purification process. When added to water, they dissolve and react to produce two insoluble products, aluminum hydroxide and calcium sulfate. These products settle out, taking suspended solid impurities with them. Write a balanced chemical equation for the reaction. 

Each of the reactants and products is an ionic compound. Recall that the formulas of ionic compounds are determined by the charges of the ions composing each compound. The formula reaction is thus written as follows. 

There is one Ca atom on each side of the equation, so the calcium atoms are aheady balanced. There are two A1 atoms on the left and one A1 atom on the right. Placing the coefficient 2 in fi-ont of Al(OH)3 produces the same number of A1 atoms on each side of the equation. 

checldng SO4 ions shows that there are three 504 ions on the left side of the equation and only one on the right side. Placing the coefBcient 3 before CaS04 gives an equal number of SO ions on each side. 

There are now three Ca atoms on the right, however. By placing the coefficient 3 in fi-ont of Ca(OH)2, we once again have an equal number of Ca atoms on each side. This last step also gives six OH ions on both sides of the equation. 

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