Hal is mixing bug spray for his roses. he has one gallon with a mixture of 90% water and 10% chemical. however, he needs a mixture that is 96.5% water. how much water should be added to the mixture to make it 96.5% water?

Overall material and component balances are important concepts to be able to answer the question above. Let x be the amount of water in gallons that should be added to his available mixture. From both balances, the equation below is obtained. 
 
                        (1)(0.90) + (x)(1) = (1 + x)(0.965)

The equation above shows the balance for water. Solving for x gives an answer of x = 1.857.

Therefore, Hal should add approximately 1.857 gallons of pure water.