Question

what is the concentration of hydrogen ion, H+, present in a water sample if 100. ml of the sample requires 7.2 ml of 2.5 x 10 -3 M NaOH to be neutralized

Answer 1

Answer: 1.8x10^-4 M H+

Explanation: The number of moles of NaOH added to the 100 ml soultion will be equal to the number of moles of H+ present in that solution.

Moles NaOH in 7.2 ml of 2.5x10^-3 M NaOH

(2.5x10^-3 M NaOH) is the same as 2.5x10^-3 moles NaOH/liter

(2.5x10^-3 moles NaOH/liter)*(7.2 ml)*(1 liter/1000ml) = 1.8x10^-4 moles NaOH used to titrate 100 ml of the acid. That means there was 1.8x10^-4 moles of H^+ in 100 ml.

Concentration of H^+ = (1.8x10^-4 moles H)/0.100 l) = 1.8x10^-4 M H+

(pH of 3.74)