Calculating H3O ions in a drop of water at 25 °C

[ducmod]

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!

 

[Borek]

You do understand the difference between number of moles and number of ions?

 

[ducmod]

You do understand the difference between number of moles and number of ions?

Oh! What a shame ) Sorry. Yes. I have to multiply my moles 5 x 10^-12 by 6.022 x 10^23
Thank you!