Achieve #6, week 2

[Tianna Nguyen 1I]

"Classify these salts as acidic, basic, or neutral: KCl, LiClO₄, K³PO₄, NH₄ClO₄, NaF."
How do I identify an acidic/basic/neutral salt?

[Lauren Woodward 1I]

Typically, if you see the cation of a strong base (ie group 1/2 metal) paired with a weak acid, the salt is basic. If there is an anion of a strong acid (ie Cl-, Br-,I-) paired with a weak base, the salt is acidic. If the cation of a strong base is paired with an anion of a strong acid, the salt is neutral. The cations and anions of strong bases and acids are spectator ions, so they don't exactly contribute to the pH, but the weak acids and bases they get paired with as the salts pull H+ and OH- from the water respectively. Pulling H+ increases pH (makes more basic) and pulling OH- decreases pH (makes more acidic).

[Shania Garrison Discussion 3E]

One great tip for these is that if the anion or cation comes from a strong acid or strong base, then it will act as a spectator ion and will not affect the pH. If it comes from a weak acid or weak base, the it will affect the pH.

This idea comes from the fact that salts are produced in acid base reactions (which from salt and water).

[Rio Gagnon 1G]

Split the salt into its cation and anion. If it comes from a strong acid or base, then its conjugate is weak, so it does not affect the pH. However, if it comes from a weak acid, the conjugate base is strong, so the salt is basic, as is the case for Na2S. The same is true for a weak base, which has a strong conjugate acid, making the salt acidic, which is true for NH4ClO4.

[Jocelyn Chin 1K]

Hi! I like to split the compound into a cation and anion. If the cation is something you would see in a strong base like Na+, and the anion is from a weak acid like F-, then the salt is basic. This is because NaF + H2O --> NaOH+ HF. The NaOH will dissociate completely and you will be left with Na+, OH-, and HF in the solution, and since there's a lot of OH, the solution will become basic. If you have a weak base cation and strong acid anion, things will be opposite, and you will have an acidic solution. If both ions are strong base and strong acid, the solution will be neutral. If both ions are from a weak base and weak acid, the solution will be really close to neutral.

[Diego Salgues 2K]

Hi! I like to split the compound into a cation and anion. If the cation is something you would see in a strong base like Na+, and the anion is from a weak acid like F-, then the salt is basic. This is because NaF + H2O --> NaOH+ HF. The NaOH will dissociate completely and you will be left with Na+, OH-, and HF in the solution, and since there's a lot of OH, the solution will become basic. If you have a weak base cation and strong acid anion, things will be opposite, and you will have an acidic solution. If both ions are strong base and strong acid, the solution will be neutral. If both ions are from a weak base and weak acid, the solution will be really close to neutral.

How do we know NaOH will dissociate?

[Jocelyn Chin 1K]

Hi! I like to split the compound into a cation and anion. If the cation is something you would see in a strong base like Na+, and the anion is from a weak acid like F-, then the salt is basic. This is because NaF + H2O --> NaOH+ HF. The NaOH will dissociate completely and you will be left with Na+, OH-, and HF in the solution, and since there's a lot of OH, the solution will become basic. If you have a weak base cation and strong acid anion, things will be opposite, and you will have an acidic solution. If both ions are strong base and strong acid, the solution will be neutral. If both ions are from a weak base and weak acid, the solution will be really close to neutral.

How do we know NaOH will dissociate?

NaOH is a strong base, and all strong bases/acids dissociate completely! You just have to memorize all the strong bases and acids.

[Ishant Goel 2D]

"Classify these salts as acidic, basic, or neutral: KCl, LiClO₄, K³PO₄, NH₄ClO₄, NaF."
How do I identify an acidic/basic/neutral salt?

This is basically how I identified each one. In the book, the process is the first look at the anion of the compound and identify if it is the conjugate base of a weak acid. If the anion is neither acidic or basic, then you look at the cation. You have to check whether the cation is one of those small highly charged acidic metal ions or the conjugate acid of a weak base. If the cation turns out to be one of these two choices and the anion turns out to be the conjugate base of a weak acid, then you have to consider both equilibria but we haven't been given any examples like that here. For example lets look at KCl. The anion Cl- is the conjugate base of a strong acid and rule is that if it is the conjugate base of a strong acid, it's basically neutral in solution. The cation is K+, which is a part of Group 1 and Group 2 metals. The rule is that the metals that belong in these groups are neutral in solution so KCl is neutral in solution. One more example we can consider is NaF. The anion F- is the conjugate base of a weak acid, meaning that it will produce a basic solution. Na+ as a cation is neutral in solution, as it belongs to Group 1. Therefore, this solution with NaF will be basic.

[Harshitha_Pandian_3F]

Specifically for neutral salts, they are either made from a strong base or a strong acid meaning that in water they barely disassociate. This means that they barely have any effect on the pH of the substance.

[Nithya Madhu 2L]

Hey,
For these questions consider the following:
If you have a strong base cation and strong acid anion, it will be neutral.
If you have a strong base cation and weak acid anion, it will be a base since the weak acid can't neutralize the strong base.
If you have a weak base cation and a strong acid anion, it will be an acid since the weak base can't neutralize the strong acid.

For example:
- KCl, contain a strong base cation (K) and the anion of a strong acid (Cl), so it is neutral
- NH4Br contains a weak base cation (NH4) and a strong acid anion (Br), so it is an acid
Hope that helps!