[Knighteres]

If not, how can i find the [H+] or [OH-] concentration of a solution with only the molar concentration (M)? i always thought it was the same thing, but today i was doing homework and the [H+] concentration i got from molar concentration looked a bit odd to me, and their phs were very low, but i didnt care until one of the phs i got from that was negative, and i think that is not possible.

if it was JUST a problem of that specific ph, how can i find the [H+] concentration of a strong acid solution in water knowing the density (g/ml) and the m/m % ?? thanks

[Babcock_Hall]

If the [H⁺] is 10 M, what would you calculate the pH to be?

[Knighteres]

If the [H⁺] is 10 M, what would you calculate the pH to be?

   -log[10] right? so -1? is this good? can a ph be -0.95? is a HCl solution on 35% m/m with density 0.95... please some insight?

[Babcock_Hall]

Yes, your calculation of -1 for the pH looks fine, and there is no reason why pH cannot be a negative number.  However, your density of 0.95 does not look correct.  The density of hydrochloric acid at this concentration is greater than one.