Concept Attainment P H

Arrhenius Theory of Acids and Bases ,[object Object],[object Object],[object Object],[object Object],[object Object],HCl (g) H + (aq) + Clˉ (aq) H 2 O NaOH (s) Na + (aq) + OHˉ (aq) H 2 O H + (aq) + OHˉ (aq) H 2 O (l)

Br ø nsted Lowry Acid/Base Theory NaOH(s) + H 2 O(l) Na + (aq) + OHˉ(aq) HBr(g) + H 2 O(l) H 3 O + (aq) + Brˉ(aq) ,[object Object],[object Object],H 3 O + (aq) + OHˉ (aq) 2 H 2 O (l)

Br ø nsted Lowry Acid/Base Theory ,[object Object],[object Object],[object Object],[object Object],[object Object],NH 3 + H 2 O NH 4 + + OHˉ conjugate acid conjugate base acid base NH 3 + H 2 O NH 4 + + OHˉ base acid NH 4 + + OHˉ NH 3 + H 2 O base acid

Review Question ,[object Object],Question: For each of the following chemical equations, identify the acids and bases in both the forward and reverse reactions. i) HClO 2 + H 2 O ClO 2 ˉ + H 3 O + ii) OClˉ + H 2 O HOCl + OHˉ iii) NH 3 + H 2 PO 4 ˉ NH 4 + + HPO 4 2 ˉ conjugate acid conjugate base acid base conjugate acid conjugate base acid base conjugate acid conjugate base acid base

Last two things ,[object Object],[object Object]

Concentration is measured in M ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

What happens when the concentration gets really small? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Let’s apply this concentration & scientific notation stuff to Acids/Bases ,[object Object],[object Object],[object Object],[object Object]

Let’s apply this concentration & scientific notation stuff to Acids/Bases ,[object Object],[object Object],[object Object],[object Object],[object Object]

Now, let’s use the scientific notation… ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Regardless of the acid’s identity, the concentrations of H + ions rank as follows:

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],So, we might as well just write…

Now, for the NEW idea: pH ,[object Object]

Part 1: Define a logarithm ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Part 2: How do we change the log result into a positive number? Multiply the log by -1 to change it to positive ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

It’s LOG!!!! ,[object Object],[object Object],[object Object],[object Object]

Part 3: pH ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

So, what is pH ? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Find the pH of each of the following ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],pH 6 14 2 12 3 13

What did you notice about the pH scale compared to concentration? The smaller the pH the higher the concentration of the [H + ]

Let’s try our using pH to rank acid strength

The following are ranked from LEAST to GREATEST [H + ] ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],The smaller the pH the higher the concentration of the [H + ]

Why use pH? ,[object Object],[object Object],[object Object]

The pH scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14

The Acid Concentration Scale When [H + ] = 1 x 10 to the… -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14

Let’s see if the pH concept makes sense to you ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

pOH: the flip-side of pH ,[object Object],[object Object],[object Object]

The pOH scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14

The Base Concentration Scale When [OH - ] = 1 x 10 to the… -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14

Find the pOH of each of the following ,[object Object],[object Object],[object Object],[object Object],pOH 6 14 2

What’s the relationship between pH and pOH? ,[object Object]

pH and pOH ,[object Object],pH = -log[H 3 O + ] pOH = -log[OH - ] [H 3 O + ][OH - ]= 1.0x10 -14 pH + pOH = 14

Sample Question ,[object Object],HBr + H 2 O H 3 O + + Brˉ For our purposes H 3 O + and H + can be considered equivalent terms pH = -log [H + ] pH = -log (0.1) pH = 1.0 Since pH + pOH = 14 1.0 + pOH = 14 pOH = 13

Another Sample Question ,[object Object],KOH is a strong base and will fully dissociate; [OHˉ] = 0.10M Method # 2 Calculate pOH pOH = -log [OH ˉ ] pOH = -log (0.1) pOH = 1.0 pH + pOH = 14 pH + 1 = 14 pH = 13 Calculate pH

Why pH/pOH?? Autoprotolysis of Water H 2 O + H 2 O H 3 O + + OH - base acid c. acid c. base K c = [H 2 O][H 2 O] [H 3 O + ][OH - ] K W = K c [H 2 O][H 2 O] = = 1.0x10 -14 [H 3 O + ][OH - ] K W = = 1.0x10 -14 [H 3 O + ][OH - ]

Concept Attainment P H

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Concept Attainment P H