Arrhenius and CALCULATIONSDecember log10108, 2.009 * 103

Objective: SWBAT calculate pH and pOH using known

concentrations

Catalyst: Which is a stronger acid, one with a pH of 5

or one with a pH of 3? Which is a stronger base, one with a pH of

11 or one with a pH of 14? Which is a stronger acid, one with a pH of 9

or one with a pH of 10?

Agenda

Catalyst What’s a pirate’s favorite model of acid

and bases? ARR-Henius!

Now, calc it out, calc it out, calc it out. Reference sheet!

Practice Exit Question

Arrhenius Model for Acids and Bases Key Point #1:

Arrhenius said: Acids will dissociate (separate) to produce hydrogen ions Bases will dissociate (separate) to produce hydroxide ions

An Arrhenius acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in aqueous solution

HCl H+ + Cl- A Arrhenius base is a substance that contains

hydrogen and ionizes to produce hydroxide ions in aqueous solution

NaOH Na+ + OH-

This is called DISSOCIATION!

Practiccce…. Are these Arrhenius acids or bases? HCl Mg(OH)2

H2SO4 Ca(OH)2

HNO3

NaOH H2CO3

NH4OH

Concentration!

Now, we talked yesterday about how pH measures how STRONG or WEAK an acid or a base is.

What do you think would make an acid STRONGER? More H+ or less H+

What do you think would happen to the pH? IT WOULD DECREASE!

Concentration!

Now, we talked yesterday about how pH measures how STRONG or WEAK an acid or a base is.

What do you think would make an base STRONGER? More OH- or less OH-

What do you think would happen to the pH? IT WOULD INCREASE!

How do we measure how much of something there is? CONCENTRATION!

In chemistry terms, we call this MOLARITY.

Key Point #2: Concentration is measured in molarity and is used to calculate pH and pOH.

WHAAAAT THE HEEEECKK? What’s pOH????!??!???! Just like pH- which measures the

Hydrogen ions, pOH measures the hydroxide ions.

pOH is just used less commonly… With pOH…

Acids > 7 Bases < 7

Ready to calculate?

Your equations are on the blue sheet, but you need to know when to use the right ones…

Let’s practice this skill first.

How do you pick equations?

Find the equation where the thing that you are looking for is BY ITSELF and the thing that you have is in the equation!

What is the pH of a solution with 3.2 * 10-3 M [H+]?

What is the [OH-] of a solution with a pOH of 12?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Let’s practice

Logarithims are functions that deal with exponents. Unfortunately, we do not

have time to deal with all the funness of logs- Algebra 2 will though!

What is the [H+] of a solution that has a pH of 7?

[H+] = 10-pH

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Let’s practice

What is the [H+] of a solution that has a pH of 9?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Your turn

What is the [OH-] of a solution with a pOH of 12?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Let’s practice

What’s the pOH of a solution with pH of 3?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Let’s practice

What’s the pH of a solution with a pOH of 6?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Your turn

What’s the pH of a solution that has 4.1 * 10-3 M [H+]?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Your turn

What’s the pH of a solution that has 1.0 * 10-5 M [H+]?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Your turn

What’s the pOH of a solution that has 3.4 * 10-3 M [OH-]?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Your turn

What’s the pOH of a solution that has 1.7 * 10-4 M [OH-]?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Tricksters…

What’s the pOH of a solution that has an [H+] of 1.3 * 10-3 M?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

Tricksters…

What’s the pH of a solution that has an [OH-] of 2.2 * 10-6 M?

EQUATIONS!

pH= -log [H+]

[H+] = 10-pH

pOH= -log [OH-]

[OH-]= 10-pOH

pH+pOH=14

This is your time to shine…

Figure out those last problems!

Exit Question

If a solution has a [H+] of .01, what is the pH of that solution?

What is the pOH of that solution?