Ok so i have this question to figure out. What is the pH of a solution having an H2CO3 concentration of 10-7 mol l-1? Now here is the info i've been given to learn about pH in my lecture notes. That pH is the negative log to base 10 of the concentration of hydrogen ions in a solution. It says that for pure water pH=-log10[H+ (aq)] For pure water [H+] = 10-7 mol l-1 Therefore pH of pure water is -log10 10-7=7 Two questions... a) Why does H+ = 10-7 mol l-1 in pure water? What is it about H20 that actually tells me that? How do you work out the concentration of H+ in H20 b) why do you have an H+ in water when its H20? when I think about water it is balanced by 2H to an O so why are there ions? Or is it saying that the amount of H+ in water is 10-7 mol -1 as an overall figure ? Its just that i thought that the anions in O balanced the cations in H perfectly so why am I being told about the amount of H+ in water? Is this why water has a pH of 7 and is neutral pH? As you can see I am quite confused. How would I be able to work out the concentration of H+ ions in a solution of H2CO3 10-7 mol l-1? I don't really understand the concept and have been quite confused by any online material I have come across. Links to any simple explanations would be appreciated as well as any comments.