Water pulls itself apart!Water pulls itself apart!

= HH++ + OH + OH--

HH33OO++ + OH + OH--

OROR

Bond breaking

Since water pulls itself apart….Since water pulls itself apart….

HOHHOH(l) (l) <-------------> H<-------------> H+1+1 + OH + OH-1-1

We can write a KWe can write a Kspsp or K or Kww = [H = [H++][OH][OH--]]

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[H[H22O]O] Only one out of ten million water Only one out of ten million water

molecules dissolve, so….molecules dissolve, so….

This equals [1 x 10This equals [1 x 10-7-7M][1 x 10M][1 x 10-7-7M]M] ----------------------------------------------------------

[1][1]

Water has a KWater has a Kww = 1 x 10 = 1 x 10-14-14MM Once again, this means only one out of Once again, this means only one out of

every ten million water molecules breaks every ten million water molecules breaks apart!apart!

Most of water is just that…. Most of water is just that…. Undissociated, unbroken, whole, not Undissociated, unbroken, whole, not dissolved water!dissolved water!

This natural balance in a glass of water This natural balance in a glass of water can be upset by dissolving substances in can be upset by dissolving substances in a glass of water that have either Ha glass of water that have either H++ or OH or OH- -

in them - this will increase the Hin them - this will increase the H+ + or OHor OH-- to to an amount more than 1 x 10an amount more than 1 x 10-7-7M….M….

These substances are known as…………These substances are known as…………

ACIDS AND BASES!!!!!!!ACIDS AND BASES!!!!!!!

Acids are ionic substances that have Acids are ionic substances that have HH++ acting as the metal! acting as the metal!

Examples: HCl, H(NOExamples: HCl, H(NO33), H), H22(SO(SO44)) Bases are ionic substances that have Bases are ionic substances that have

OHOH-- acting as the non-metal! acting as the non-metal!

Examples: Na(OH), Ca(OH)Examples: Na(OH), Ca(OH)22, K(OH), K(OH)

What happens when these substances What happens when these substances dissolve in water?dissolve in water?

Acids, Like HCl, break apart Acids, Like HCl, break apart in water! in water!

HCl --------> HHCl --------> H+ + + Cl+ Cl--

HCl + HOH --------> HHCl + HOH --------> H33OO+ + + Cl+ Cl--

This causes the balance to be This causes the balance to be upset!upset!

No longer is there an equal amount No longer is there an equal amount of Hof H++ and OH and OH-- (1 x 10 (1 x 10-7-7M of each). M of each). Now there is more HNow there is more H++, or H, or H33OO++, and , and

this means you have an ACID!!!this means you have an ACID!!!

Bases, like NaOH, break apart Bases, like NaOH, break apart in water!in water!

NaOH --------> NaNaOH --------> Na+ + + OH+ OH--

This causes the balance to be This causes the balance to be upset!upset!

No longer is there an equal amount No longer is there an equal amount of Hof H++ and OH and OH-- (1 x 10 (1 x 10-7-7M of each). M of each). Now there is more OHNow there is more OH--, and this , and this means you have a BASE!!!means you have a BASE!!!

How do we determine if we How do we determine if we have an acid or a base???have an acid or a base???

If the HIf the H+ + concentration is higher in a concentration is higher in a solution than the OHsolution than the OH-- concentration, concentration, we have an ACID.we have an ACID.

If the OHIf the OH- - concentration is higher in a concentration is higher in a solution than the Hsolution than the H++ concentration, concentration, we have a BASE.we have a BASE.

What is the pH scale?What is the pH scale?

The pH scale is an easy way to The pH scale is an easy way to measure whether you have an acid measure whether you have an acid or a base…….or a base…….

It ranges from 1 to 14:It ranges from 1 to 14: Anything with a pH of 1 to 6 is an Anything with a pH of 1 to 6 is an

acid, anything with a pH of 8 to 14 is acid, anything with a pH of 8 to 14 is a base, and pH 7 is neutral, or water!a base, and pH 7 is neutral, or water!

H+1 concentration

pH = -log H+1

acidic basic

pH is a measure of……pH is a measure of……

The amount of HThe amount of H++ or acid that is or acid that is present in solution……present in solution……

We find pH by taking the - log of [HWe find pH by taking the - log of [H++] ] concentration:concentration:

pH = -log [H+]

pH = -log [H+]

How does that translate into How does that translate into pH????pH????

If a solution has a concentration of If a solution has a concentration of [H+] ions that = 1 x 10[H+] ions that = 1 x 10-2-2M, that is M, that is extremely high and the pH = 2 - this extremely high and the pH = 2 - this is an acid!!!is an acid!!!

If a solution has a concentration of If a solution has a concentration of [H[H++] ions that = 1 x 10] ions that = 1 x 10-11-11M, that is M, that is extremely low and the pH = 11- this is extremely low and the pH = 11- this is a base!a base!

Let’s go back and look at the Let’s go back and look at the KKw w for water….for water….

[H[H++][OH][OH--] = 1 x 10] = 1 x 10-14-14M……M…… ------------------------------

[H[H22O]O] Why is this….?Why is this….? This is a natural balance in the universe….This is a natural balance in the universe…. Water always balances itself….Water always balances itself…. If there is too much HIf there is too much H+1+1, then the H, then the H+1 +1 will react with any OHwill react with any OH-1-1

in the water to reform HOHin the water to reform HOH This will dramatically decrease the amount of OHThis will dramatically decrease the amount of OH-1-1 in the in the

waterwater The balance will always equal 1 x 10The balance will always equal 1 x 10-14 -14 though!though! So…….So…….

HOHHOH(l) (l) <-------------> H<-------------> H+1+1 + OH + OH-1-1

If [HIf [H++] is high, say at 1 x 10] is high, say at 1 x 10-2-2M, then the [OHM, then the [OH--] concentration is low, and would ] concentration is low, and would equal…..equal…..

[1 x 10[1 x 10-2-2M][ OHM][ OH--] = 1 x 10] = 1 x 10-14-14MM[OH[OH--] = 1 x 10] = 1 x 10-12-12MM

The pH of this solution would be:The pH of this solution would be:- - log [1 x 10- log [1 x 10-2-2M] = 2M] = 2

Why, again, would the [OHWhy, again, would the [OH--] be so low…?] be so low…? The reverse reaction is going to occur when you dump in so much [HThe reverse reaction is going to occur when you dump in so much [H++] into the ] into the

water…water…

HH+1+1 + OH + OH-1 -1 <-------------> HOH<-------------> HOH(l) (l)

And more water is going to be made…And more water is going to be made… Your [OHYour [OH--] concentration is going to go way down, and get used up!] concentration is going to go way down, and get used up! Because your [HBecause your [H++] concentration is so extremely high, because you added so ] concentration is so extremely high, because you added so

much extra, there is going to be tons of it left over, even though some of it got much extra, there is going to be tons of it left over, even though some of it got used up!used up!

The two together will still equal 1 x 10The two together will still equal 1 x 10-14-14 though! though!

[H[H++][OH][OH--] = [H] = [H++][OH][OH--] = [H] = [H++][OH][OH--] = 1 x 10] = 1 x 10-14-14M M

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[H[H22O] [1]O] [1]

•Why did the concentration of the water become 1?