A salt is an ionic compound consisting of a cation other than H+ and an anion other than OH minus. Here, we’ll show you all about hydrolysis of ions in.

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Presentation transcript:

A salt is an ionic compound consisting of a cation other than H+ and an anion other than OH minus. Here, we’ll show you all about hydrolysis of ions in salts.

A salt can either be acidic (click) neutral, or (click) basic depending the on the hydrolysis of it ions. Acidic Basic NeutralSalts

We’re sometimes given the formula for a salt and asked to determine whether it is acidic, basic, or neutral when dissolved in water.

There is a step by step process we can use to determine whether a given salt is acidic, basic or neutral in aqueous solution. Process for Determining Whether a Salt is Acidic, Basic, or Neutral 1.Write a dissociation equation for the salt to find its cation and anion. 2.Eliminate any spectator ions. 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis. 4.If both ions undergo hydrolysis, use K a and K b values to determine which hydrolysis is predominant.

Step 1 is to write a dissociation equation for the salt in order to determine what its cation and anion are. Process for Determining Whether a Salt is Acidic, Basic, or Neutral 1.Write a dissociation equation for the salt to find its cation and anion. 2.Eliminate any spectator ions. 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis. 4.If both ions undergo hydrolysis, use K a and K b values to determine which hydrolysis is predominant.

Step 2 is to eliminate any spectator ions. Process for Determining Whether a Salt is Acidic, Basic, or Neutral 1.Write a dissociation equation for the salt to find its cation and anion. 2.Eliminate any spectator ions. 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis. 4.If both ions undergo hydrolysis, use K a and K b values to determine which hydrolysis is predominant.

Remember, spectator cations are the positive ions of Group 1, or alkali metals, and Group 2, or alkaline earth metals. 1 2 The Spectator Cations

So these ions are always neutral in aqueous solution. 1 2 The Spectator Cations Always Neutral in Aqueous Solution

The spectator anions are the top 5 ions on the right side of the acid table. They are perchlorate, iodide, bromide, chloride, and nitrate. The Spectator Anions

These ions do not react with water and are always neutral in aqueous solution. They do NOT react with water and are always NEUTRAL in aqueous solutions The Spectator Anions

We can list all the spectator cations and spectator anions in a single box and use this whenever we have to determine whether a salt is acidic, basic, or neutral. 1 2 Spectator Cations Spectator Anions The Spectator Ions It’s good to memorize these!

It is a good idea to memorize these in order to save time later. At this point you may want to pause the video, take a screen shot of this and print it. 1 2 Spectator Cations Spectator Anions The Spectator Ions It’s good to memorize these!

Once we have eliminated the spectator ions, the third step is to locate the remaining ion or ions on the acid table. If an ion is not a spectator ion, that means it must undergo either acid or base hydrolysis, or both. Process for Determining Whether a Salt is Acidic, Basic, or Neutral 1.Write a dissociation equation for the salt to find its cation and anion. 2.Eliminate any spectator ions. 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis. 4.If both ions undergo hydrolysis, use K a and K b values to determine which hydrolysis is predominant.

In Chemistry 12, these are the four cations that hydrolyze. They all undergo acid hydrolysis. Cations that Hydrolyze or Fe 3+ or Cr 3+ or Al 3+

Notice the three hydrated cations, iron(III), chromium(III), and aluminum can be depicted either in their hydrated (or hexaaquo) form, Cations that Hydrolyze or Fe 3+ or Cr 3+ or Al 3+

or in the form of simple ions with a 3+ charge. Cations that Hydrolyze or Fe 3+ or Cr 3+ or Al 3+

When you dissociate a salt, you’re likely to see these cations depicted in this simple form. Cations that Hydrolyze or Fe 3+ or Cr 3+ or Al 3+ or NH 4 +

Just keep in mind that if you need to write a hydrolysis equation for one of these three, you must (click) convert them to their hydrated form Cations that Hydrolyze or Fe 3+ or Cr 3+ or Al 3+ or NH 4 +

The other hydrolyzing cation, ammonium, always appears as NH4 plus or in compound formulas as NH4. Cations that Hydrolyze or Fe 3+ or Cr 3+ or Al 3+

Now for anions. Anions are on the right side of the acid table. We’ll start by looking at anions that undergo ONLY base hydrolysis. Anions that Undergo ONLY Base Hydrolysis

That’s these ions here. Anions that Undergo ONLY Base Hydrolysis

Excluding the spectator ions on the top right of the table, these are all the ions on the right with a negative charge, whose formulas do NOT start with “H”. Anions that Undergo ONLY Base Hydrolysis

Amphiprotic anions are the negative ions on the right side, whose formulas start with an “H” Amphiprotic Anions Undergo BOTH Acid and Base Hydrolysis

Amphiprotic anions undergo BOTH acid and base hydrolysis. What we have to do with these is determine which hydrolysis is predominant. How to do that is shown on the video “Hydrolysis of Amphiprotic Anions” Amphiprotic Anions Undergo BOTH Acid and Base Hydrolysis

Here are the amphiprotic anions. Notice their formulas all start with “H” and they all have negative charges. Amphiprotic Anions Undergo BOTH Acid and Base Hydrolysis

The fourth step of our process comes into play in cases where both the cation and anion of the salt hydrolyze. Process for Determining Whether a Salt is Acidic, Basic, or Neutral

If both cation and anion hydrolyze, we compare the value of the Ka for the cation to the value of Kb for the anion in order to decide which hydrolysis is predominant. We’ll go through an example of this later. Process for Determining Whether a Salt is Acidic, Basic, or Neutral 1.Write a dissociation equation for the salt to find its cation and anion. 2.Eliminate any spectator ions. 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis. 4.If both ions undergo hydrolysis, use K a and K b values to determine which hydrolysis is predominant.

Now we’ll go through a few examples working with salts.

We’re asked to determine whether the salt calcium nitrite, with the formula Ca NO2 two, is acidic, basic, or neutral when dissolved in water. Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral?

The first step in our process is to write the dissociation equation for the salt. Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? Process for Determining Whether a Salt is Acidic, Basic, or Neutral 1.Write a dissociation equation for the salt to find its cation and anion.

We start with the formula Ca (NO2) 2. Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 1.Write a dissociation equation for the salt to find its cation and anion.

It dissociates into a calcium ion, Ca 2 plus, Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 1.Write a dissociation equation for the salt to find its cation and anion.

And two nitrite, or NO2 minus ions. Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 1.Write a dissociation equation for the salt to find its cation and anion.

The second step in the process is to eliminate any spectator ions. Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 2.Eliminate any spectator ions.

Because it’s a member of group 2, the calcium ion is a spectator ion, so it can be (click) eliminated. Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 2.Eliminate any spectator ions.

Now that we have eliminated the spectator ion, the next step is to locate the remaining ion, nitrite, on the table. Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis.

The nitrite ion is on the right side of the acid table, in the weak base section. It does not start with an “H”, so it is not amphiprotic. It undergoes only base hydrolysis. Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis.

Therefore, we can say that NO2 minus is basic. (pause) Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis. basic

Because Ca2+ is a neutral spectator and (click) NO2 minus is basic Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis. basic A neutral spectator

We can say that the salt Ca(NO2)2, or calcium nitrite, is basic. So we’ve now answered this question. Is the salt calcium nitrite, Ca(NO 2 ) 2, acidic, basic, or neutral? 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis. A neutral spectator The salt Ca(NO 2 ) 2 is BASIC basic

We’re asked to determine whether the salt potassium iodide, with the formula KI, is acidic, basic, or neutral when dissolved in water. Is the salt potassium iodide, KI, acidic, basic, or neutral?

We start by writing the dissociation equation for KI Is the salt potassium iodide, KI, acidic, basic, or neutral?

Its KI gives K+ plus I minus. Now we eliminate spectator ions Is the salt potassium iodide, KI, acidic, basic, or neutral?

K+ is in group 1, (click) so it is a neutral spectator which can be eliminated. Is the salt potassium iodide, KI, acidic, basic, or neutral?

And I minus is one of the top 5 ions on the right side of the acid table, (click) so it is also a neutral spectator, which can be eliminated. Is the salt potassium iodide, KI, acidic, basic, or neutral?

So both the cation and the anion of this salt are neutral spectator ions, Is the salt potassium iodide, KI, acidic, basic, or neutral? A neutral spectator

Therefore the salt, KI, is neutral. Is the salt potassium iodide, KI, acidic, basic, or neutral? A neutral spectator The salt KI is NEUTRAL

Here’s another example. We’re asked to determine whether the salt chromium(III) nitrate, with the formula Cr(NO3)3, is acidic, basic, or neutral when dissolved in water. Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral?

We’ll start by writing the dissociation equation for Cr(NO3)3 Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral?

We get the cation Cr 3+ or chromium(III) and (click) the anion NO3 minus, nitrate. Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral?

Cr 3+ is not in group 1 or 2 on the periodic table, so it is not a spectator cation Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral?

But the anion NO3 minus is one of the top 5 neutral spectator ions on the right side of the table, (click) so it can be eliminated. Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral?

Going back to Cr 3+, Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral?

Cr 3+, or chromium(III), is one of the acidic cations. Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral?

So we can say that Cr 3+ is acidic. Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral? acidic

Because Cr 3+ is acidic, (click) and NO3 minus is a neutral spectator, Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral? A neutral spectator acidic

We can say the salt Cr(NO3)3 is acidic Is the salt chromium(III) nitrate, Cr(NO 3 ) 3, acidic, basic, or neutral? acidic A neutral spectator The salt Cr(NO 3 ) 3 is ACIDIC

Here’s one more example. We’re asked to determine whether the salt ammonium oxalate, with the formula (NH 4 ) 2 C 2 O 4, is acidic, basic, or neutral when dissolved in water. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

We start by writing the dissociation equation for (NH 4 ) 2 C 2 O 4. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

So we have the cation NH 4 +, and (click) the anion C 2 O 4 2 minus Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

The cation NH 4 +, is one of the 4 acidic cations on the left side of the acid table. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

So we can say that NH4 + is acidic. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral? acidic

The anion C2O4 2 minus is found on the right side of the acid table, in the weak base section. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

So we can say that C2O4 2 minus is basic. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral? acidicbasic

We see that neither the cation nor the anion of this salt are spectators. They both hydrolyze. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral? acidicbasic Neither of these are spectator ions

Remember, if both cation and anion hydrolyze, we compare the value of the Ka for the cation to the value of Kb for the anion in order to decide which hydrolysis is predominant. Process for Determining Whether a Salt is Acidic, Basic, or Neutral 1.Write a dissociation equation for the salt to find its cation and anion. 2.Eliminate any spectator ions. 3.Locate the remaining ions on the acid table and decide whether they undergo acid or base hydrolysis. 4.If both ions undergo hydrolysis, use K a and K b values to determine which hydrolysis is predominant.

So we compare the Ka of NH4 + with the Kb of C2O4 2 minus Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

Here, we’ll start by finding the value of Kb for the oxalate ion, C2O4 2 minus. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

We locate the ion C2O4 2minus on the right side of the acid table. This is the row we will work with to find its Kb Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

Remember the Kb of a species is Kw divided by the Ka of its conjugate acid. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

The conjugate acid of C 2 O 4 2 minus is HC 2 O 4 minus Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

The value of Kw is 1 × 10 –14. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

And the value of Ka for HC2O4 minus is 6.4 × 10 –5. This appears in the acid table on the right end of the row for hydrogen oxalate, or HC2O4 minus. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

So the value of Kb is 1 × 10 –14 divided by 6.4 × 10 –5, Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

Which comes out to 1.6 × 10 –10. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

So we can summarize by saying that the value of Kb for C 2 O 4 2 minus is 1.6 × 10 –10. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

Now, we’ll find the value of Ka for the cation, NH 4 plus Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

The value of Ka for NH4 plus can be found directly on the right side of the row for NH4 plus. (click) It is 5.6 × 10 –10. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

We see that Ka for the cation is 5.6 × 10 –10 and (click) Kb for the anion is 1.6 × 10 –10, Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

So the value of Ka for the cation is greater than the value of Kb for the anion. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral?

Therefore, the salt (NH 4 ) 2 C 2 O 4 is acidic. And we’ve now answered this question. Is the salt ammonium oxalate, (NH 4 ) 2 C 2 O 4, acidic, basic, or neutral? The salt (NH 4 ) 2 C 2 O 4 is ACIDIC

So, in summary, by knowing how ions hydrolyze,

we can find out whether any given salt is acidic, basic, or neutral when dissolved in water