# does increasing the concentration of HCl increase ph? (1 Viewer)

#### girlworld_club

##### Member
i was just thinking this in term of water, say i had 100ml then added another 1000ml then the ph would still be neutral. However, according to the formula ph should change. can someone clear this up. thanks

#### Riproot

##### #MedLyf
HCl is not neutral...

So adding more (moles of) HCl into the same volume of water would decrease the pH, because HCl has a low pH.

#### Riproot

##### #MedLyf
E.g. If you have a HCl/H2O solution with 0.010 moles of HCl and 1.0L of water the concentration would be:
c = n/v
c = 0.010 moles/1.0L
c = 0.010 moles/L

since, doing HSC Chem, we can assume HCl dissociates completely, we can say
[H+] = 0.010 M
so,
pH = -log[H+]
pH = -log[0.01]
pH = 10

Therefore, adding more HCl to this, let's say 0.10 moles, would increase the concentration.

n = 0.010 moles + 0.10 moles
n = 0.11 moles

Therefore,
c = n/v
c = 0.11 moles/1.0L
c = 0.11 moles/L

since, doing HSC Chem, we can assume HCl dissociates completely, we can say
[H+] = 0.11 M
so,
pH = -log[H+]
pH = -log[0.11]
pH = 0.95860731484...
pH = 0.96 (2 significant figures)

#### someth1ng

##### Retired Nov '14
i was just thinking this in term of water, say i had 100ml then added another 1000ml then the ph would still be neutral. However, according to the formula ph should change. can someone clear this up. thanks
Doesn't even make sense. pH of HCl solution won't be neutral.

#### girlworld_club

##### Member
^ i meant *say i had 100ml of water (oops)

#### someth1ng

##### Retired Nov '14
The formula says the pH would change...

pH=-log[H+]

[X] means concentration of X.

#### bedpotato

##### Member
When you add water to water (I'm assuming this is what you're trying to say), it self ionises.
H2O + H2O --> H3O+ + OH-

In water, pH = pOH

If water is neutral i.e. a pH of 7, then [H+] = 10^-7
Now pOH.
pOH = 14 - pH = 7
so [OH-] = 10^-7

[H+] = [OH-]

Even if you add more water, [H+] will always equal [OH-], so the pH will remain the same.

Idk how to explain...

• Parvee

#### AnimeX

##### Member
If you increase the concentration of HCl the pH will decrease (more acidic), not increase.