Acids and Bases

Acids and Bases

By Mihir Paranjape

Acids

Acids release H⁺ (protons) in solutions.

HCl > H⁺ + Cl^-​

• Sour Taste

• Electrolytes: Can conduct electricity.

• React with Metals

• Turn Blue litmus Red

• Have pH <7​

Bases

Bases release OH^- in solutions.

NaOH > Na⁺ + OH^-​

• Bitter Taste

• Electrolytes: Can conduct electricity.

• Soapy Touch​

• React with Acids

• Turn Red litmus Blue

• Have pH >7​

pH

pH = -log [H⁺]

• pH is also called the power of Hydrogen.

• [H⁺] = concentration of H⁺ in M (moles/L)​

• It is a number between 0 and 14

• Low pH means more [H⁺] - stronger acid.

• Higher pH means lower [H⁺] - weaker acid.

• Acids have pH 0-7​

pH

pH = -log [H⁺]

​Calculate pH of a 0.001 M HCl solution?

We know that HCl splits into H+ and Cl- ions.

HCl is a strong acid and therefore [H+] =[HCl] = 0.001 M

​

pH = -log (0.001) = -(-3) = 3​

pH

pH = -log [H⁺]

​Calculate pH of if [H+] = 2.31 x 10^-5 M

​

pH = -log (2.31 x 10^-5) = -(-4.64) = 4.64​

Multiple Choice

If a solution has a [H⁺] of 9.3x10^-11, what is the pH?

• 10.0

• 4.0

• 3.5

• 8.2

pOH

pOH = -log [OH^-]

• pOH is also called the power of OH.

• [OH^-] = concentration of OH^- in M (moles/L)​​

• It is a number between 0 and 14

• Low pOH means more [OH^-] - stronger base.

• Higher pH means lower [OH^-] - weaker base.

• Bases have pH 7-14

Multiple Choice

If the [OH-] of a solution is 2.7 x 10^-4 mol/L the pOH of the solution is

• 10.44
• 3.56
• 1.00
• -4.43

pH + pOH = 14

• You can calculate one from the other using this equation.

​

E.g. Calclate the pOH if pH = 4.64

​pH + pOH = 14

4.64 + pOH = 14​

pOH = 14-4.64 = 9.36​

pH + pOH = 14

• You can calculate one from the other using this equation.

​

E.g. Calclate the pH if [OH^-] = 5.67 x 10^-6 M

Since OH- is given, we can calculate pOH = -log( 5.67 x 10^-6 )

pOH = 5.25​

pH + pOH = 14​

pOH = 14-5.25 = 8.75​

Multiple Choice

A  pH and a pOH will add up to:

• 0
• 7
• 14
• 1.0 x 10^-14

Multiple Choice

if the [H+] of a solution is 8.4 x 10^-3 mol/L the pOH of the solution will be

• 2.08
• 11.92
• 1.02
• 12.98

Multiple Choice

If the pH of a solution is 5.6 the pOH is

• 6.5
• 12.4
• 8.4
• 5.6

[H⁺] = 10 ^-pH

If you know the pH, you can calculate the [H⁺] concentration in M.

​

E.g. Calculate the [H⁺] if pH is 3.4?

​[H⁺]​ = 10 ^-3.4​ = 0.000398 M or 3.98 x 10^-4 M

​

Calculate ​the [H⁺] if pOH is 3.4?

First calculate the pH = 14 - 3.4 = 10.6

Next ​[H⁺]​ = 10 ^-10.6​ = 2.51 x 10^-11 M

[OH^-] = 10 ^-pOH

If you know the pOH, you can calculate the [OH^-] concentration in M.

​

E.g. Calculate the [OH^-] if pOH is 8.9?

​[OH^-]​ = 10 ^-8.9​ = 1.26 x 10 ^-5 M

​

Calculate ​the [OH^-] if pH is 2.3?

First calculate the pOH = 14 - 2.3 = 11.7

Next ​[OH^-]​ = 10 ^-11.7​ = 2 x 10^-12 M

Multiple Choice

The pH of a solution is 8.43. What is the [H⁺]concentration?

• 3.7 x 10 ^-9

• 1.0 x 10^-8.43

• 2.7 x 10^-6

• 1.0 x 10^-14

Multiple Choice

If a solution has a pOH of 3.7 the [OH-] of the solution is

• 5.0 x 10^-11

• 2.0 x 10^-4

• 10.3

• 14

Multiple Choice

Oranges have a [H⁺] of 1.7 x 10^-2 M. Their pOH is

• 1.77

• 12.23

• 10.91

• 3.09

Multiple Choice

What is the [H+] if the pH is 4.0?

• 1.0 x 10^-10 M

• 1.0 x 10^-14 M

• 1.0 x 10^-4 M

• 1.0 x 10^-7 M

Titration Curves

If you start with an Acid, you will start with a low pH.

If you now add a Base to this, the Base will react with the acid thereby reducing the [H+] and increase pH slowly.

This will happen till the solution reaches a pH of 7 at which point it is neither an acid or a base, this is called the end point or equivalence point.

The Graph of pH vs volume added is called a Titration curve.​

Multiple Choice

What is the end point or equivalence point of this Titration?

• 10 mL

• 20 mL

• 30 mL

• 40 mL

Multiple Choice

What is the volume of NaOH added at the end point of this titration?

• 20

• 40

• 60

• 80

Multiple Choice

How much HCl has to be added to the base to complete the titration?

• 10

• 40

• 50

• 60