4.6 – Associate the pH scale with the scale of the molar concentrations of H+ and OH– ions.

4.7 – Explain the molar concentration of H+ and OH- ions in pure water based on its pH value and molecular formula.

436pH VALUES

(molar concentrations of H+ and OH- ions)

ACIDS BASES

Contain greater number of H+ ions

than OH- ions(pH of 1-7)

Contain less H+ ions than OH- ions

(pH of 7-14)Neutral Solutions

Contain an equal number of H+ ions and OH- ions

(pH of 7 (water))

IMPORTANT INFORMATION:- Level of acidity and basicity is

based on the nature of the acid or base and its concentration

- pH is expressed as the positive value of an exponent in H+ ion concentration

[H+] x [OH-] = 1 x 10-14 mol/L

(FORMULA For H+ and OH- Ions)

This formula is used to find the concentrations of H+ ions and OH- ions in various solutions

pH is expressed as the positive value of an exponent in H+ ion concentration

H+ ions(concentration)

OH- ions(concentration))

pH

1. 0.1 mol/L of HCl 1.0 x 10-1 1.0 x 10-13mol/L 12. 0.001 mol/L of HCl 1.0 x 10-3 1.0 x 10-11mol/L 33. 0.1 mol/L of NaOH 1.0 x 10-13 1.0 x 10-1mol/L 13

The product of [H+] ions and [OH-] ions is always = 1.0 x10-14 mol/L

The Concentration of H+ ions for water is always = 1.0 x 10-7

- mol/L

pH is always the positive value of the exponent for the H+ ions

0.5 L

To find the pH we must know the concentration of the H+ ions. Use the formula to find this:

The hydroxide ion concentration (OH-) of a solution is 1 x 10-12. What is the pH of this solution?

[H+] x [OH-] = 1 x 10-14 mol/L[H+] X 1x10-12 = 1x10-14

[H+] = 1x10-2

Change into pH value

[H+] = 1x10-2 pH of 2

0.5 L

To find the pH we use the H+ ion concentration

The hydrogen ion concentration [H+] of a solution is 1 x 10-5. What is the pH of this solution?

EXAMPLE # 2EXAMPLE # 2

[H+] = 1x10-5

Change into pH value by taking the positive exponet of the H+ concentration

pH of 5

0.5 L

To find the pH we must find the molar concentration first.

Jason is asked to mix 1.825 grams of HCl with 5 L of water. What is the pH of his solution?

It is an acid so….

[H+] = 1x 10-2 pH of 2

nC=L

0.05C=5 L

n = grams molar mass

n = 1.825 36.5 g/mol

n = 0.05 moles

C= 0.01 mol/LMolar concentration is

For the H+ ions since this is

an acid!

Tricky

0.5 L

To find the pH we must find the molar concentration first.

Mindy is working in a lab and is asked to mix 10 grams of NaOH with 2.5 L of water. What is the pH of her solution?

Since it is a base, the OH- is….[OH-] = 1x 10-1

pH of 13

nC=L

0.25C=2.5 L

n = grams molar mass

n = 10 40 g/mol

n = 0.25 moles

C= 0.1 mol/LMolar concentration is

For the OH- ions since this is a

base!

Tricky

Therefore the H+ ions is [H+] = 1x 10-13

KEY POINTS The formula for concentration of

H+ and OH- ions is as follows:[H+] x [OH-] = 1 x 10-14 mol/L

The Concentration of H+ ions for water is always = 1.0 x 10-7- mol/L

pH is always the positive value of the exponent for the H+ ions

Worksheet #4 Study guide, Module 3, page 32 and

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