Na and Cl's influence on pH

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Isaac Wen
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Na and Cl's influence on pH

Postby Isaac Wen » Thu Dec 10, 2020 11:14 pm

Hi! In one of the lectures, Dr. Lavelle mentioned that Na+ and Cl- do not affect the pH of the solution they're in. Why is that? And if there's a rule that explains this phenomenon, can the same thing be applied to all Group 1 and Group 17 elements?

Kailani_Dial_2K
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Re: Na and Cl's influence on pH

Postby Kailani_Dial_2K » Thu Dec 10, 2020 11:21 pm

Na+ is a conjugate acid of a strong base. Since it is from a strong base it is therefore a weak acid which means that it is unlikely that it will repick-up the OH- that it gave to water. Cl- is a conjugate base of the strong acid HCl. Since it is from a strong acid it is therefore, a weak base. This means that it is umlikley to pick up an H again. Therefore, Cl- and Na+ do not interact with the water molecules, so they don't increase the hydroxide or hydronium ions and therefore do not affect pH. This can be applied to any conjugate acid/base that comes from a strong acid/ base.

Eliot Kagan 2G
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Re: Na and Cl's influence on pH

Postby Eliot Kagan 2G » Fri Dec 11, 2020 9:18 pm

Rather than not interacting, Na+ isn't strong enough to make the water molecules lose a hydrogen like Fe, Cr, Al, Cu, and Ni.
A general rule to follow is that the cations in groups 1 and 2 aren't strong enough to affect the pH.

For anions, the really strong anions create a more basic solution because they take an H+ from the surrounding water and create OH-.
If you want more info, I recommend checking out the 12/7 lecture.

Kamille Kibria 2A
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Re: Na and Cl's influence on pH

Postby Kamille Kibria 2A » Sat Dec 12, 2020 9:02 pm

i did not understand this either but the rule i follow that helped me out a lot is that if the element is associated with a strong acid or strong base, it will not affect the pH of the solution. Cl is associate w strong acid HCl and Na is associated w strong base NaOH. this is because if you were to dissolve either Cl or Na (separate) in H20, it will not increase the concentration of H3o+ or OH-

Justin Nguyen 3E
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Joined: Wed Sep 30, 2020 9:35 pm

Re: Na and Cl's influence on pH

Postby Justin Nguyen 3E » Sat Jan 16, 2021 10:19 pm

What helped me understand the effect of Na+ and Cl- on pH was that because both atoms possess filled valence shells, they don't have an inclination to take or give protons/electrons, thus not affecting pH.


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