anions are negative ions and some of them undergo hydrolysis when they are mixed with water. here,...

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

Hydrolysis of

Anions

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.


The top 5 ions on the right side of the acid

table

Remember, these are all strong acids.


These are all strong acids

So these ions are the conjugate bases of strong acids.


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.


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.


These reactions can ONLY go forward

For example, HClO4 will readily lose a proton to form ClO4 minus


HClO4 will readily lose a proton to form ClO4

–

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.


ClO4– cannot gain a

proton to form HClO4

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

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 solutionsThey are called

Spectator Ions

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

Why isn’t HSO4– a spectator ion?

After all, it’s conjugate acid, H2SO4, is a strong acid

Why isn’t HSO4– 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


Which means they all accept a proton from a water molecule.

Act as weak

bases in water

Accept a proton

from water


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

–O

CO

O

–

23CO

H

HO

2H O

These two species will (click) collide with each other

–O

CO

O

–

23CO

H

HO

2H 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

CO

O

–

23CO

HO

2H O

H+

H+

Because this oxygen atom has gained an electron, it will (click) acquire a negative charge

–O

CO

O

–

23CO

HO

2H O

–

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

–O

CO–

23CO

HO

2H O

–H+O

OH

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

OCO–

23CO

HO–H+

–HO

3HCOOH

H

We now have the bicarbonate ion, HCO3 minus

OCO–

HO–O

3HCOOH

These ions now move away from each other.

HOCO–

O

3HCO

HO–

OH

Now, we can write the equation for the hydrolysis of the carbonate ion, It’s (click) CO3 2 minus

23 2 3CO H O HCO OH

+ +

Hydrolysis of CO32–

Plus H2O

23 2 3CO H O HCO OH

+ +


Gives HCO3 minus

23 2 3CO H O HCO OH

+ +


Plus OH minus

23 2 3CO H O HCO OH

+ +


Basically, this is just (click) a proton transfer from a water molecule to the carbonate ion,

23 2 3CO H O HCO OH

+ +


H+

Forming a bicarbonate ion, HCO3 minus

23 2 3CO H O HCO OH

+ +


H+

And a hydroxide ion, OH minus

23 2 3CO H O HCO OH

+ +


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.

2 2 2NO H O HNO OH

Hydrolysis of Some Anions

2F H O HF OH

6 5 2 6 5C H COO H O C H COOH OH 2

2 4 2 2 4C O H O HC O OH

3 2 3CH COO H O CH COOH OH

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.

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


None of these can donate a

proton

So all of these can undergo base hydrolysis

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


All of these undergo base

hydrolysis

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

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


We write down NO2 minus

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


Because its hydrolysis, we add water.

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


NO2 minus is a weak base, so it takes a proton from water,

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


weak base

Forming its conjugate acid, HNO2,

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


And a hydroxide ion.

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


Next, we’ll do the hydrolysis equation for F minus,

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


Being a weak base, F minus

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


Reacts with water by taking a proton from it,

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


Producing its conjugate acid, HF,

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH



2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


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

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


We’ll start by writing C6H5COO minus

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


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

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


Forming its conjugate acid, C6H5COOH

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH



2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


Now we’ll do the oxalate ion, C2O4 2 minus

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


C2O4 2 minus

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


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

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


the oxalate ion gains a proton to form the binoxalate or hydrogen oxalate ion, HC2O4 minus

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


and water loses a proton to form a hydroxide ion.

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


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

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


CH3COO minus

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


Hydrolyzes by removing a proton from water,

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


To form its conjugate acid, CH3COOH

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


And a hydroxide ion

2 2 2NO H O HNO OH


2F H O HF OH


2 4 2 2 4C O H O HC O OH


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.

2 2 2NO H O HN OHO


2F H O HF OH


2 4 2 2 4C O HO OH HC O


The anions here all undergo base hydrolysis, producing

hydroxide ions.

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

anions are negative ions and some of them undergo hydrolysis when they are mixed with water. here,...

Documents

water anions

spectator anions

video anions

hydrolyzing anions

spectator ions

weak acid

acid table

weak bases