Mixing Acids and Bases

Acids and pH: 
A measure of the hydrogen ion concentration [H⁺], pH is calculated using the following formula: 

• pH = -log₁₀[H⁺]   

Hydrogen ion concentration [H⁺] can be calculated using the following formula:  

• [H⁺] = 10^-pH

Example One (pH):

Find the pH of a 0.2 M solution of HCl: 

• Write the balanced equation for the dissociation of the acid:
• HCL ==> H⁺(aq) + Cl^-(aq) 
• Use the equation to find the [H⁺]: 
• 0.2 M x (1/1) = 0.2 M of [H⁺] **HCl is a strong acid which fully dissociates** 
• Calculate pH: 
• pH = -log₁₀[H⁺]   
• pH = -log₁₀[0.2]  
• pH = 0.7 

Example Two (pH):

Find the pH of a 0.2 M solution of H₂SO₄: 

• Write the balanced equation for the dissociation of the acid:
• H₂SO₄ ==> 2H⁺(aq) + SO₄^2- (aq) 
• Use the equation to find the [H⁺]: 
• 0.2 M x (2) = 0.4 M of [H⁺] **H₂SO₄ is another strong acid which fully dissociates** 
• Calculate pH: 
• pH = -log₁₀[H⁺]   
• pH = -log₁₀[0.4]  
• pH = 0.4 

Example Three (pH):

Find the [H⁺]  of a nitric acid solution with a pH of 3.0: 

• Use the formula to find the [H⁺]: 
• pH = 3.0 
• [H⁺]  = 10^-pH 
• [H⁺]  = 10^-3.0 
• [H⁺]  = 0.001 M

• Check it: 
• pH = -log₁₀[H⁺]   
• pH = -log₁₀[0.001]  
• pH = 3.0 

Bases and pOH: 

A measure of the hydroxide ion concentration [OH^-], pOH is calculated using the following formula: 

• pOH = -log₁₀[OH^-]    

Hydroxide ion concentration [OH^-] can be calculated using the following formula:  

• [OH^-] = 10^-pOH 

Example One (pOH):

Find the pOH of a 0.1 M solution of NaOH: 

• Write the balanced equation for the dissociation of the base:
• NaOH ==> Na⁺(aq) + OH^-(aq) 
• Use the equation to find the [OH^-]: 
• 0.1 M x (1) = 0.1 M of [OH^-] **NaOH is a strong base which fully dissociates** 
• Calculate pH: 
• pH = -log₁₀[OH^-]   
• pH = -log₁₀[0.1]  
• pH = 1 

Example Two (pOH):

Find the pOH of a 0.1 M solution of Ba(OH)₂: 

• Write the balanced equation for the dissociation of the base:
• Ba(OH)₂ ==> 2OH^-(aq) + Ba²⁺ (aq) 
• Use the equation to find the [OH^-]: 
• 0.1 M x (2) = 0.2 M of [OH^-] **Ba(OH)₂ is another strong base which fully dissociates** 
• Calculate pH: 
• pH = -log₁₀[OH^-]   
• pH = -log₁₀[0.2]  
• pH = 0.7 

Example Three (pOH):

Find the [OH^-]  of a sodium hydroxide solution with a pOH of 1.0: 

• Use the formula to find the [OH^-]: 
• pH = 3.0 
• [OH^-]  = 10^-pOH 
• [OH^-]  = 10^-1.0 
• [OH^-]  = 0.1 M

• Check it: 
• pH = -log₁₀[OH^-]   
• pH = -log₁₀[0.1]  
• pH = 1.0   

Another formula to know from this unit that greatly simplifies things is:

• **pH and pOH = 14**

- Simon Sierra, George Spencer and Ben Suratos