effects on pH

Moderators: Chem_Mod, Chem_Admin

Katie Bart 1I
Posts: 104
Joined: Sat Aug 24, 2019 12:16 am

effects on pH

Postby Katie Bart 1I » Tue Jan 21, 2020 10:31 am

Why do conjugate bases/acids and group 1/2 cations not affect pH?

Posts: 106
Joined: Sat Sep 14, 2019 12:16 am
Been upvoted: 1 time

Re: effects on pH

Postby Veronica_Lubera_2A » Tue Jan 21, 2020 10:50 am

I think you're mentioning solubility rules so you don't include groups 1 and 2 in the reaction because they don't affect pH (totally dissolve in water and are present on both sides of the reaction so you can cancel them out). Example is NaOH and also salts like NaCl don't affect pH. Conjugate bases/acids though of relevant molecules will affect pH.

Kaylee Clarke 1G
Posts: 103
Joined: Fri Aug 30, 2019 12:15 am

Re: effects on pH

Postby Kaylee Clarke 1G » Tue Jan 21, 2020 11:44 am

Group 1/2 cations are considered spectator ions and therefore are insignificant.

Posts: 221
Joined: Fri Aug 09, 2019 12:16 am

Re: effects on pH

Postby Brian_Ho_2B » Tue Jan 21, 2020 12:41 pm

The general rule is that the stronger an acid/base is, the weaker its conjugate. The weaker an acid/base is, the stronger its conjugate. Group 1/2 cations (with the exception to Magnesium, but that's a topic for a more advanced chemistry class) do not affect pH because they are mostly stable and those ions are not strong enough to break the O-H bonds in water to act as a base. However, transition metal cations that are highly charged (eg. +3) are very polarizing and can affect pH.

Posts: 107
Joined: Sat Aug 17, 2019 12:15 am

Re: effects on pH

Postby pmokh14B » Tue Jan 21, 2020 12:54 pm

Because those conjugates are more stable than their respective acids/bases, so they stay in solution rather than reacting to form hydronium or hydroxide.

Jainam Shah 4I
Posts: 130
Joined: Fri Aug 30, 2019 12:16 am

Re: effects on pH

Postby Jainam Shah 4I » Wed Jan 22, 2020 1:19 am

Group 1 and group 2 cations are typically cations from a strong acid or base. For example the Na+ of NaOH and K+ from KOH. If you look at the reaction for both of these in the presence of water you would see that since these are strong bases they full disassociate. The cation thus has no point or ability to participate in a reverse reaction and is basically an extremely weak conjugate acid that cannot contribute to the pH. Like the others said it is also a spectator ion on both sides of the reaction so it doesn't change the concentration.

Posts: 102
Joined: Fri Aug 30, 2019 12:17 am

Re: effects on pH

Postby ThomasNguyen_Dis1H » Wed Jan 22, 2020 1:35 am

Conjugate acids or conjugate bases of strong acids are very weak. This is due to the fact that Kw=Ka*Kb. Since Kw is a constant, when one of the K increases the other must decrease. So take for example HCl, it will have a very high Ka value since it dissociates completely which means the Kb will be a very small value which represents the conjugate base of Cl-.

Ruth Glauber 1C
Posts: 100
Joined: Wed Sep 18, 2019 12:20 am

Re: effects on pH

Postby Ruth Glauber 1C » Wed Jan 22, 2020 3:09 pm

They're considered spectator ions and insignificant!

Return to “Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions”

Who is online

Users browsing this forum: No registered users and 1 guest