(7-8) What are the concentrations of the and the LiOH?
The key to solving problems of this sort is to keep track of the moles used. The number of moles in 30 mL of LiOH exactly neutralizes the number of moles in 50 mL of . The number of moles in 26.8 mL of LiOH exactly neutralizes the number of moles of after some of the acid has been neutralized by KOH. These relationships allow for two simultaneous equations in two unknowns, which can then be solved to give the original concentrations.
First, it is necessary to find the number of moles of acid neutralized by the potassium hydroxide. One mole of KOH exactly neutralizes one mole of . Therefore, the number of moles neutralized by the potassium hydroxide is
Then let x be the molarity of the perchloric acid and y be the molarity of the lithium hydroxide. The volume of the liquid multiplied by the molarity gives the number of moles present in the liquid. Since the number of moles of perchloric
