BELLWORK- Label pairs

Identify the conjugate acid-base pairs

a. H2S + H2O HS- + H3O+

b. HClO4 + H2O ClO4- + H3O+

c. NH3 + H2O NH4+ + OH-

d. H2O + HNO3 NO3- + H3O+

The pH scale measures the hydrogen ion concentration[H+]

of a solution.

A pH of 7 is neutral

A pH less than 7 is acidic (litmus is red)

A pH greater than 7 is basic (litmus is blue)

The pH scale ranges from below zero (very acidic) to above14 (very basic)

The pH scale is not linear.The pH scale is logarithmic.

pH = -log[H+] [H+] = 1.0 x 10-2 pH = 2 very acidic[H+] = 1.0 x 10-3 pH = 3 acidic

A solution with pH of 2 contains 10 times as much H+ as a solution with pH of 3.

Calculate pHpH = -log [H+]

[H+] = 1.0 x 10-7M

[H+] = 5.0 x 10-5M

Calculate pHpH = -log [H+]

[H+] = 1.0 x 10-7M pH= -(exponent) =7

[H+] = 5.0 x 10-5M

Calculate pHpH = -log [H+]

[H+] = 1.0 x 10-7M pH= -(exponent) =7

[H+] = 5.0 x 10-5M pH is between 4&5

Calculate pHpH = -log [H+]

[H+] = 1.0 x 10-7M pH= -(exponent) =7

[H+] = 5.0 x 10-5M pH is between 4&5

to CHECK with calculator1.Enter concentration in calculator

2.Press log key

3.Change sign to positive

OR in the reverse order depending on your calculator!

Calculate [H+] given pH

pH = 7.0

pH= 8.5

Calculate [H+] given pH

pH = 7.0 [H+]= 1x10-7

pH= 8.5

Calculate [H+] given pH

pH = 7.0 [H+]= 1x10-7

pH= 8.5 [H+]= 3.2x10-9

Calculate [H+] given pH

pH = 7.0 [H+]= 1x10-7

pH= 8.5 [H+]= 3.2x10-9

1. Enter pH value in calculator

2. Press the +/- key

3. Press the 10x key

OR in the reverse order depending on your calculator!

From pH0 to pH14 the H+ concentration decreases 100,000,000,000,000 times!!

Relationship between [H+] and [OH-]

[H3O+][OH-] = 1.0 x 10-14

ALWAYS!!

Relationship between [H+] and [OH-]

[H3O+][OH-] = 1.0 x 10-14

ALWAYS!!

If [H+] = 1.0 x 10-5 then,

[OH-] = 1.0x10-14/ 1.0x10-5 = 1 x 10-9

SUBTRACT THE EXPONENTS!

Relationship between [H+] and [OH-]

[H3O+][OH-] = 1.0 x 10-14

If [H+] = 5.0 x 10-4 then,

[OH-] = 1.0x10-14/ 5.0x10-4 = 2 x 10-11

Acidic = more H+ Basic = more OH-

pOH = -log[OH-]

pH + pOH = 14

Always!!

Relationship between pH and pOH

pH pOH

[H+] [OH-]

pH + pOH = 14

[H+][OH-]=1x10-14

pH = -log[H+]

pOH = -log[OH-]

pH pOH

[H+] [OH-]

pH + pOH = 14

[H+][OH-]=1x10-14

[H+] =10-pH

[OH-]=10-pOH

Calculate pH pOH

What is the pH of a solution with pOH = 13?

Is the solution acidic or basic?

What is the pOH of a solution with pH = 8?

Is the solution acidic or basic?

What are the concentrations of H+ and OH-?