1. Solving Acid and Base Equilibrium SCH4U0

2. Power of Hydrogen • In acidic and basic solutions, we gauge the level of acidity using the pH scale • pH = power of hydrogen • The pH scale is a logarithmic scale of hydronium concentration in a solution • Because it is a negative logarithm, low numbers represent high concentrations of hydronium

3. Power of Hydrogen Basic Low [ Acidic High • We can define a similar scale in terms of hydroxide concentration called pOH • The “p” means “negative logarithm of” • pOH is similar to pH, low pOH means high hydroxide concentration

4. pOH Scale • Both the pH and pOH scale are logarithmic, meaning that each unit represents a 10x difference from the previous unit • Eg: • A solution with pH 1 contains 10x more hydronium than one with pH 2 • A solution with pOH 1 contains 10x more hydroxide than one with pH 2

5. Autoionization of Water • The hydroxide and hydronium concentrations in water are linked together due to the autoionization of water • When either hydronium or hydroxide is added to water, the equilibrium shifts left, reducing the other concentration

6. Kw Equation • We can use the Kw equation to relate pH and pOH • Take the negative log of both sides

7. Solving pH and pOH • Lets use our knowledge of acid/base strength to determine the pH and pOH of certain systems • Eg: What is the pH, pOH, and hydroxide concentration in a 0.050M solution? • Nitric acid is a strong acid, so it dissociates 100%

8. Solving pH and pOH • Using this, we can easily calculate pH and pOH

9. Weak Acids/Bases • Solving the pH/pOH becomes a little more interesting when we consider weak acids and bases. • Eg: What is the pH, pOH, and hydroxide concentration in a 0.10 M ascorbic acid () solution? • What is the dissociation equation for this compound? • If we look up the Ka/Kb, ascorbic acid is a decent weak acid but a terrible base • To determine pH, pOH, and the hydroxide concentration we will need to determine the hydronium concentration by solving the EQ.

10. Sample Problem • Fill in the ICE chart

11. Sample Problem • To solve we select the most useful method • Try the assumption • If it doesn’t work, solve the quadratic equation The assumption is valid

12. Solving pH and pOH • Using this, we can easily calculate pH and pOH

13. Practice • Try the following problem yourself • Eg: What is the pH, pOH, and hydronium concentration in a 0.40 M hydrazine () solution? • What is the dissociation equation for this compound? • If we look up the Ka/Kb, hydrazine is a decent weak base but a terrible acid

14. Sample Problem • Fill in the ICE chart

15. Sample Problem • To solve we select the most useful method • Try the assumption • If it doesn’t work, solve the quadratic equation The assumption is valid

16. Solving pH and pOH • Using this, we can easily calculate pH and pOH