Acid/Base Definitions pH and pOH calculations

Evaluation/Assessment: Objective: Today I will be able to: Define acid and bases based on the Arrhenius and Bronsted-Lowry definitions Calculate the pH and the pOH for a compound Evaluation/Assessment: Informal assessment – listening to student responses to questions. Listening to group interactions as the students complete the practice problems Formal assessment – analyzing student responses to the pH practice and the naming acids activity Common Core Connection Build Strong Content Knowledge Make sense of problem and persevere in solving them Reason abstractly and quantitatively Construct viable arguments and critique the reasoning of others

Lesson Sequence Evaluate: Warm-Up Evaluate: Review HW Explain: Acids and Bases Notes Elaborate: Conjugate Acid/Base Practice Explain: pH, pOH Elaborate: pH Scale Practice Evaluate: Exit Ticket

Warm - Up Name the following acids and bases HBr H2SO4 NaOH H2CO3 NH3

Objective Today I will be able to: Define acid and bases based on the Arrhenius and Bronsted-Lowry definitions Calculate the pH and the pOH for a compound

Homework Finish the pH, pOH practice

Agenda Warm-Up Acids and Bases Notes Conjugate Acid/ Base Practice pH, pOH notes pH Scale Practice Exit Ticket

ACID/BASE DEFINITIONS

3 ways to define acids and bases Arrhenius Theory Bronstead-Lowry Theory Lewis Theory – we will come back to the Lewis Definition later

What is an acid? Arrhenius Theory (Definition 1) Substance that when dissolved in water, will yield H+ ions Example HCl(aq)  H+(aq) + Cl-(aq)

What is an acid? Bronsted-Lowry Theory (Definition 2) An acid is a substance that can donate a proton Example: HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq) H3O+ = Hydronium ion

Strong Acids vs. Weak Acids Ionize almost 100% in water (react to completion) Do not ionize completely, achieve an equilibrium

Examples Strong Acids Weak Acids HCl – hydrochloric acid HBr - hydrobromic acid HI - hydroionic acid H2SO4 – sulfuric acid HNO3 - nitric acid HClO3 – chloric acid Weak Acids HF – hydrofluoric acid CH3COOH – acetic acid HCN - hydrocyanic acid

What is a base? Arrhenius Theory (Definition 1) Substance that yields hydroxide ions (OH-) as the only negative ions in an aqueous solution Example NaOH(s)  Na+(aq) + OH-(aq)

What is a base? Bronsted-Lowry (Definition 2) Any substance that can combine with or accept a proton (H+) Can be substances besides hydroxides NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)

Strong vs. Weak Bases Ionize close to 100% Reach equilibrium Examples NaOH - sodium hydroxide KOH – potassium hydroxide LiOH – lithium hydroxide Reach equilibrium Examples Most bases that are not considered strong, NH3 (ammonia)

BRONSTEAD-LOWRY CONJUGATE ACID/BASE PRACTICE You have 15 minutes to complete the practice problems

How can we measure the strength of an acid?

pH Scale A one unit change in pH represents a ten fold change in the H3O+ concentration pH = - log [H3O+] Water that falls near a coal burning power plant has a [H3O+] = 6.23 x 10-4 M. What is the pH? pH = 3.2 (acidic)

pH Scale You can also calculate [H3O+] when given a pH [H3O+] = 10-pH Human blood has a pH of 7.3. Calculate the [H3O+] [H3O+] = 10-7.3 [H3O+] = 5.01 x 10-8 M

pH Scale Figuring out the pH of a base is a little different – use pOH pH + pOH = 14 -log [OH] = pOH What is the pH of a NaOH solution that has a [OH] of 0.025 M? -log [0.025] = 1.6 = pOH 14 - 1.6 = 12.4 = pH

Disclaimer Acid-Base strength is the not the same as concentration Strength – the amount of ionization or breaking apart that a particular acid or base undergoes Concentration – amount of acid or base that you initially have You can have a concentrated solution of weak acid, or a dilute solution of a strong acid, or a concentrated solution of a strong acid, etc…

PH SCALE PRACTICE Complete the practice at your desk. Problems not completed in class will become your homework

Exit Ticket Name the following bases NaOH NH3 LiOH KOH