Higher concentration of H+ means lower ph and lower ph means it's more acidic, right?

Question

than how come HCl is the known strongest acid when it has only 1 H?

Answer 1

higher concentration of H+ means lower ph and lower ph means it's more acidic, right?

Yes, right.

The pH scale is 1,2,3,4, 5,6,7,8,9,10,11,12,13,14

1-7 is acidic

7-14 is basic at 25 degrees C

the strongest acid is pH=1, the stronges base is pH=14

that is because pH= - log(H+)

asking like you asked is same if you asked how could be so cold when it is only - 3o degrees C

Answer 2

The definition of a strong acid is a substance that will dissociate in water to produce a high concentration of H+ ions. If you dissolve 1mol HCl in 1 litre of water, then the HCl will ionise:

HCl <=> H+  +  Cl-

Because HCl is a strong acid, it will ionise completely, giving 1mol H+ in the litre of water. We say [H+] =1.00

pH = -log [H+]

pH = -log 1

pH = 0

In contrast, NH4+  ion does not ionise to give any H+ ions. (NH4+ is an ion itself). Therefore it cannot be an acid.

You cannot count the H in the compound molecule or ion, to determine if the substance is an acid or not. It is the concentration of H+ ions that are produced that determines whether it is an acid and whether it is a strong acid or a weak acid.