Na and Cl's influence on pH
Moderators: Chem_Mod, Chem_Admin
Na and Cl's influence on pH
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?
-
- Posts: 185
- Joined: Wed Sep 30, 2020 9:44 pm
- Been upvoted: 5 times
Re: Na and Cl's influence on pH
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.
-
- Posts: 100
- Joined: Wed Sep 30, 2020 10:08 pm
Re: Na and Cl's influence on pH
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.
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.
-
- Posts: 101
- Joined: Wed Sep 30, 2020 9:52 pm
Re: Na and Cl's influence on pH
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-
-
- Posts: 102
- Joined: Wed Sep 30, 2020 9:35 pm
Re: Na and Cl's influence on pH
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.
-
- Posts: 101
- Joined: Fri Sep 24, 2021 5:01 am
Re: Na and Cl's influence on pH
Na+ can't influence the pH of a solution since it's from group 1 on the periodic table. Cl- can also not affect pH because it has a full valence shell, making it not interact with other atoms.
-
- Posts: 102
- Joined: Fri Sep 24, 2021 5:12 am
Re: Na and Cl's influence on pH
Na is the conjugate of a strong base NaOH and Cl is the conjugate of a strong acid HCl, therefore when it forms NaCl, it becomes neutral.
-
- Posts: 104
- Joined: Fri Sep 24, 2021 7:08 am
Re: Na and Cl's influence on pH
NaCl is neutral and does not affect pH because Na and Cl are conjugates of strong acids and bases. When they come together, they are neutral.
-
- Posts: 103
- Joined: Fri Sep 24, 2021 7:06 am
Re: Na and Cl's influence on pH
You have to focus on if they are very weak conjugate bases or acids (which are from strong bases or acids). As for Na+, it is a weak conjugate acid of a strong base NaOH, and Cl- is a weak conjugate base of a strong acid HCl. Therefore, when they are in an aqueous solution, they are not accepting H+, nor donating H+ to the H20 molecules, and not affecting the pH either.
-
- Posts: 100
- Joined: Fri Sep 24, 2021 6:52 am
- Been upvoted: 1 time
Re: Na and Cl's influence on pH
You first take NaCl, look at Na+ and Cl- separately, and determine their respective conjugate acid/base. The conjugate base of Na+ is NaOH and the conjugate acid of Cl- is HCl. Since they are both strong, we can conclude that their subsequent acid/base of Na+ and Cl- will be weak, and therefore will not affect the pH.
-
- Posts: 107
- Joined: Fri Sep 24, 2021 5:12 am
Re: Na and Cl's influence on pH
I think they won’t affect pH because Na+ is in group now and Cl- is the conjugate base of a strong acid.
Return to “Calculating the pH of Salt Solutions”
Who is online
Users browsing this forum: No registered users and 3 guests