Hello! Here is a problem that looked easy for me, but my answer differs from the textbook's one. Please, help me to see my mistake. How many H3O ions are present in one drop (0.050 mL) of pure water at 25 °C? Here is how I solved it: There are 1.0 x 10^-7 in one liter. We have 0.000050 liters, hence 0.00005 x 1.0 x 10^-7 = 5 x 10^-12 The book gives 3 x 10^12 Thank you!