Question

0.10 g of hydrogen chloride (HCl) is dissolved in water to make 2.5 L  of solution. What is the pH of the resulting hydrochloric acid solution? Express the pH numerically to two decimal places.

0.20 g of sodium hydroxide (NaOH) pellets are dissolved in water to make 6.5 L of solution. What is the pH of this solution? Express the pH numerically to two decimal places.

Answer 1

(a). Calculate the molar concentration of HCl as follows: Given mass 0.10 g Moles of HCl = -=0.002 74mol Molar mass 36.461 g/mol Concentration of HC1 = Moles Volume=0.00274molx 2.5L=0.00685M pH=-log[H] =- log (0.00685) = 12.16 (b). Calculate the molar concentration of NaOH as follows: Moles of NaOH = Given mass_ 0.20g -=0.005 mol Molar mass 40g/mol Concentration of HCI = Moles Volume=0.005 molx6.5L=0.0325M POH=- log[OH-] =-log(0.0325) =1.489 pH=14-POH =14-1.489 = 12.51