A common salt in contct with atmoshere has pH is- Why?

Question

A)3.5 B)5 C)7 D)14

Answer 1

B.
atmosphere is slightly acidic because of CO2 (natural in all places) and SO2,NO2,SO3 (in some polluted places)

Answer 2

You mean a salt solution, right? Because if you had a block of NaCl, for instance, you might have a little bit of moisture absorbed from the air, but not much, and I don't know if it would be enough to even register a pH on a piece of litmus paper -- you've got to get it wet for it to detect anything. On a molecular level, you might get enough water in one region of the surface of the block of salt to dissolve a bit of CO2 from the air and form carbonic acid, which would obviously lower the pH a bit, and I suppose if you considered that region your solution, one molecule of CO2 dissolved in twenty molecules of H2O would be pretty strongly acidic, but it's hard to estimate how low the pH would go (and it would be silly to try to measure it)

In a salt solution, I would say that the pH should remain close to 7, maybe a little on the acidic side, but that would be more due to the absorption of CO2 into the solution from the surrounding air to form a weak carbonic acid solution. The salt itself (let's stick with NaCl) just dissociates into a positive and negative ion pair. Even if each one has a strong affinity and is able to separate water into hydroxide (OH-) and hydronium (H+ --> H3O+), they would be in equal proportion and form an equilibrium that still favors H2O. The only other reason you might get a lower pH is if you were using an electronic meter vs. litmus paper, because it is calibrated specifically to detect the hydronium ion (H3O+), and since there MIGHT be more floating around due to the salt, even though it's in equilibrium with hydroxide ions, the meter might detect more H3O+ around and say the solution is more acidic than it actually is. So my gut feeling is C)7, but you might get B) 5 because of the above factors. Depends on temperature, how much salt is in solution, and how you're measuring pH.

Answer 3

Answer is C) pH=7, since NaCl will not hidrolize with the water vapours in the atmosphere (NaCl does not hidrolize)