does adding solid NaCl increase the pH of a acidic solution?

last SG · 2011-10-29T21:46:21+00:00

No. Solid NaCl is neutral and its ions, Na+ and Cl- have no effect on the pH of a solution.Acidity/basicity is determined by the concentration of H+ and OH-...

SgStudentStressed SG

i thought like if the volume increase the conc of H+ ions decrease so pH increase? why wont the pH increaee?

StudentQns SG

okok so r these principles right

1) pH will only increase when the substance added into the acidic solution is in aqueous form ( NaCl (aq)) or in liquid form (H2O)

2) pH will NOT increase when the substance added into the acidic solution is a solid (NaCl (s)) despite it being a neutral salt.

Hence, solid stuff doesnt do anything only liquid or aqeuous stuff?

thanks so much n y did my 3 posts get deleted i checked the rules n didnt break any except the salts one (so sorry but cos it was like not updated)

UltimaOnline SG

okok so r these principles right

1) pH will only increase when the substance added into the acidic solution is in aqueous form ( NaCl (aq)) or in liquid form (H2O)

2) pH will NOT increase when the substance added into the acidic solution is a solid (NaCl (s)) despite it being a neutral salt.

Hence, solid stuff doesnt do anything only liquid or aqeuous stuff?

Yes.

StudentQns SG

um but why does it work like that? to aid my understanding, when calculating pH is it comparing the hyrogen ions against the hyroxide ions only or if there are Na+ or Cl- ions present it is also compared with? is its only the hydroxide ions then my understanding is: adding solid NaCl will not increase the OH- in the solution thus the conc of H+ ions dont change hence the pH does not increase.

Darkness_hacker99 SG

At O level, you will only need to know it's the H+ and OH- ions that determines the acidity or alkalinity of a solution. Since solid NaCl doesn't have any H+ ions or OH- ions, pH remains the same.

When it goes higher up at A level above, you will learn about physical and other conditions that affect pH at an indepth level.

frekiwang SG

There are many types of concentrations in science.

The concentration you are referring to is no. of moles of H+ / total volume (or total mass). However, PH is not determined by this type of concentration.

PH is determined by the no. of moles of H+ ions / total no. of moles of H+ and OH- ions. Suppose you added a certain amount of vegetable oil to the solution, obviously the volume and the mass increase at the same time, but do you think it is logical to deduce the PH value will increase?

UltimaOnline SG

There are many types of concentrations in science.

The concentration you are referring to is no. of moles of H+ / total volume (or total mass). However, PH is not determined by this type of concentration.

Because the vegetable oil and the aqueous solution are immiscible, the volume of the aqueous solution does not change, and therefore pH of each of the two solutions (oil solution and aqueous solution) remain unchanged upon adding them together (since they're immiscible and thus remain in separate layers).

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