Anions are negative ions and some of them undergo hydrolysis when they are mixed with water. Here, we’ll examine these more closely.

We will start by getting familiar with the anions that do NOT hydrolyze. Anions that do NOT hydrolyze

Anions that do NOT hydrolyze, or undergo hydrolysis, are the top 5 ions on the right side of the acid table. Anions that do NOT hydrolyze The top 5 ions on the right side of the acid table

Remember, these are all strong acids. Anions that do NOT hydrolyze These are all strong acids

So these ions are the conjugate bases of strong acids. Anions that do NOT hydrolyze They are the conjugate bases of strong acids

Even though these are on the base side of the table, (click) they are too weak to remove protons from any species, including water. Anions that do NOT hydrolyze Too weak to remove protons

The single arrows, pointing only to the right remind us that these reactions can only go in the forward direction. Anions that do NOT hydrolyze These reactions can ONLY go forward

For example, HClO4 will readily lose a proton to form ClO4 minus Anions that do NOT hydrolyze HClO 4 will readily lose a proton to form ClO 4 –

But ClO4 minus CANNOT gain a proton to form HClO4. A reaction with a single arrow on this table will not go in the opposite direction of the arrow. Anions that do NOT hydrolyze ClO 4 – cannot gain a proton to form HClO 4

So these 5 anions have no acid-base reactions These anions have no acid-base reactions

They do NOT react with water and are always NEUTRAL in aqueous solutions

Therefore, they are called spectator ions. They do NOT react with water and are always NEUTRAL in aqueous solutions They are called Spectator Ions

At this point your may ask, Why isn’t HSO4 minus a spectator ion? Why isn’t HSO 4 – a spectator ion?

After all, it’s conjugate acid, H2SO4, is a strong acid Why isn’t HSO 4 – a spectator ion? Strong Acids

It’s because HSO4 minus also appears in this location on the left side of the table. That means it can act as a weak acid. So it is NOT a spectator ion.

So the spectator ions are ClO4 minus, I minus, Br minus, Cl minus, and NO3 minus. It would be useful to memorize these, or at least remember they are the top 5 ions on the right side of the acid table. spectator anions

Now that we’ve seen which anions do not hydrolyze, we’ll now look at the anions that (click) do hydrolyze, or undergo hydrolysis. Anions that Do hydrolyze

In this video, we’ll deal only with anions that are not amphiprotic. In other words, their formulas do not begin with an “H”. They are shown here. We’ll deal with hydrolysis of amphiprotic anions in another video Anions that Hydrolyze

All these anions act as weak bases in water. Act as weak bases in water Anions that Hydrolyze

Which means they all accept a proton from a water molecule. Act as weak bases in water Accept a proton from water Anions that Hydrolyze

Here we’ll show one of these hydrolyzing anions, carbonate, CO3 2 minus (click) and a water molecule – O C O O – H H O

These two species will (click) collide with each other – O C O O – H H O

H This hydrogen atom will donate one of its shared electrons to the oxygen atom in the water molecule (click) and it will change to an H+ ion, or proton. – O C O O – H O H+H+

H+H+ Because this oxygen atom has gained an electron, it will (click) acquire a negative charge – O C O O – H O –

This proton (click) is now transferred to the carbonate ion as the water changes to an OH minus, or hydroxide ion. – O C O – H O – H+H+ O

An electron from this oxygen will move toward the proton, so this (click) negative charge disappears as the proton changes into a hydrogen atom O C O – H O – H+H+ – HO

H We now have the bicarbonate ion, HCO3 minus O C O – H O – O

These ions now move away from each other. HO C O – O H O –

Now, we can write the equation for the hydrolysis of the carbonate ion, It’s (click) CO3 2 minus ++  Hydrolysis of CO 3 2–

Plus H2O ++  Hydrolysis of CO 3 2–

Gives HCO3 minus ++  Hydrolysis of CO 3 2–

Plus OH minus ++  Hydrolysis of CO 3 2–

Basically, this is just (click) a proton transfer from a water molecule to the carbonate ion, ++  Hydrolysis of CO 3 2– H+H+

Forming a bicarbonate ion, HCO3 minus ++  Hydrolysis of CO 3 2– H+H+

And a hydroxide ion, OH minus ++  Hydrolysis of CO 3 2– H+H+

Looking on the right side of the acid table, we can find a few other non-amphiprotic anions that we can write hydrolysis equations for. Hydrolysis of Some Anions A few anions that are not amphiprotic

None of these are able to donate a proton to water. They act only as bases, not acids. Hydrolysis of Some Anions None of these can donate a proton

So all of these can undergo base hydrolysis Hydrolysis of Some Anions All of these undergo base hydrolysis

We’ll now write hydrolysis equations for these (click) starting with the nitrite ion, NO2 minus Hydrolysis of Some Anions

We write down NO2 minus Hydrolysis of Some Anions

Because its hydrolysis, we add water. Hydrolysis of Some Anions

NO2 minus is a weak base, so it takes a proton from water, Hydrolysis of Some Anions weak base

Forming its conjugate acid, HNO2, Hydrolysis of Some Anions

And a hydroxide ion. Hydrolysis of Some Anions

Next, we’ll do the hydrolysis equation for F minus, Hydrolysis of Some Anions

Being a weak base, F minus Hydrolysis of Some Anions

Reacts with water by taking a proton from it, Hydrolysis of Some Anions

Producing its conjugate acid, HF, Hydrolysis of Some Anions

And a hydroxide ion. Hydrolysis of Some Anions

Now, we’ll write an equation for the hydrolysis of the benzoate ion, C6H5COO minus Hydrolysis of Some Anions

We’ll start by writing C6H5COO minus Hydrolysis of Some Anions

Being a weak base, this also reacts with water and takes a proton from it. Hydrolysis of Some Anions

Forming its conjugate acid, C6H5COOH Hydrolysis of Some Anions

And a hydroxide ion. Hydrolysis of Some Anions

Now we’ll do the oxalate ion, C2O4 2 minus Hydrolysis of Some Anions

C2O4 2 minus Hydrolysis of Some Anions

reacts with water, removing just one proton from it. In equations for hydrolysis reactions, we always remove only one proton at a time. Hydrolysis of Some Anions

the oxalate ion gains a proton to form the binoxalate or hydrogen oxalate ion, HC2O4 minus Hydrolysis of Some Anions

and water loses a proton to form a hydroxide ion. Hydrolysis of Some Anions

the last equation we’ll do is the hydrolysis equation for the acetate or ethanoate ion, CH3COO minus Hydrolysis of Some Anions

CH3COO minus Hydrolysis of Some Anions

Hydrolyzes by removing a proton from water, Hydrolysis of Some Anions

To form its conjugate acid, CH3COOH Hydrolysis of Some Anions

And a hydroxide ion Hydrolysis of Some Anions

The anions here all undergo base hydrolysis, producing hydroxide ions. The formation of hydroxide ions in a solution, tends to make the solution more basic. Hydrolysis of Some Anions The anions here all undergo base hydrolysis, producing hydroxide ions.

So now, we’ve looked at some anions that DO hydrolyze Anions that Hydrolyze

And we must remember the anions which do NOT hydrolyze, these 5 spectator ions on the top right of the acid table. spectator anions