Acids and Bases

Properties of Acids and Bases Tart or sour taste (think of lemons) DO NOT TASTE CHEMICALS! Corrosive to metals React with bases to form a salt and water On the pH scale: acids have a pH less than 7 Litmus paper = RED BASES Bitter taste (think of baking soda) DO NOT TASTE CHEMICALS! Corrosive to organic materials React with acids to form a salt and water On the pH scale: bases have a pH greater than 7 Litmus paper = BLUE Feel slippery Breaking Bad: https://www.youtube.com/watch?v=Q32LQYCO9AA Fight Club: http://www.flickclip.com/flicks/fightclub.html

Acids Arrhenius Definition: Break apart (dissociate) to yield hydrogen ions (H+) in water (aqueous) solutions HCl H+ + Cl- HNO3 H+ + NO3- H2SO4 H+ + HSO4 - H2O H2O H2O

Naming Acids HCl H2SO3 HNO3 chloride hydro-(stem)-ic acid Anion Ending Anion Example Acid Name Example -ide -ite -ate chloride hydro-(stem)-ic acid hydrochloric acid HCl sulfite (stem)-ous acid sulfurous acid H2SO3 nitrate (stem)-ic acid nitric acid HNO3

Naming Acids Name the following acids: H2CrO4 HF H2CO3 HClO2 CH3COOH Anion Ending Acid Name -ide hydro-(stem)-ic acid -ite (stem)-ous acid -ate (stem)-ic acid

Writing Formulas of Acids Write the formulas for the following acids: Phosphorous acid Anion Ending Acid Name -ide hydro-(stem)-ic acid -ite (stem)-ous acid -ate (stem)-ic acid

Bases Arrhenius Definition: Break apart (dissociate) to yield hydroxide ions (OH-) in water (aqueous) solutions NaOH Na+ + OH- KOH K+ + OH- H2O H2O

Naming Bases Cation name + hydroxide NaOH sodium hydroxide Ca(OH)2 calcium hydroxide NH4OH ammonium hydroxide Cation name + hydroxide

Naming Bases Name the following bases: Ba(OH)2 KOH Al(OH)3 Cation name + hydroxide

More Naming Practice H3PO4 Nitrous acid Mg(OH)2 Hydrobromic acid Name the following acids/bases or write their formula: H3PO4 Nitrous acid Mg(OH)2 Hydrobromic acid Lithium hydroxide H2S Anion Ending Acid Name -ide hydro-(stem)-ic acid -ite (stem)-ous acid -ate (stem)-ic acid

Even More Naming Practice! Identify whether the following are acids or bases. Then name them! Ba(OH)2 2. H2S 3. CH3COOH 4. Fe(OH)2 5. HClO2 Anion Ending Acid Name -ide hydro-(stem)-ic acid -ite (stem)-ous acid -ate (stem)-ic acid

The pH Scale https://www.youtube.com/watch?v=z0E-Qxis4IY

Remember the household products lab? You tested household chemicals with litmus paper and pH paper. Product Color pH Formula Acid/Base? 1. 2. … 9.

What happened to the pH paper? pH paper (aka Universal Indicator Paper) What color(s) do/does the paper turn for acids? What color(s) do/does the paper turn for bases? Reds and oranges Greens and Blues

What is the pH scale? pH: stands for “potential of hydrogen” represents the hydrogen ion (H+) concentration of a solution

The pH scale Acidic solution: pH < 7.0 Neutral solution: pH = 7.0 Basic solution: pH > 7.0 Neutral ACIDIC BASIC pH = Increasing acidity Increasing basicity

The pH Scale

The pH Scale

How can you tell the pH of a chemical? Use an indicator! Indicator paper (like pH paper) Liquid indicators (like phenolphthalein) pH meters

The pH range varies for different indicators Indicator: a chemical or solution that changes color at a certain pH The pH range varies for different indicators

LAB: Fruit and Vegetable Indicators Purpose: Many naturally colored compounds can behave as acid-base indicators. In this lab, you will be given a choice of several different fruits and vegetables. Your goal is to make indicators from these fruits and vegetables. Your goal today: - With your group, write a DETAILED procedure for how you will prepare your three fruit and vegetable indicator solutions. - Get approved by me before the end of the hour.

Indicator Lab Instructions: Many naturally colored compounds can behave as acid-base indicators. In this lab, you will be given a choice of several different fruits and vegetables. Your goal is to make indicators from these fruits and vegetables. On lined notebook paper, you must do the following: Write a purpose. Provide a complete set of instructions for making the indicator solution from the raw materials and testing the solution. (The indicator is usually in the skin of the fruit or veggie. You will have to boil the fruit or veggie in a small amount of water to extract the indicator). Create a data table listing your results for 3 indicator solutions (see below). Answer the analysis questions. Available Materials: solutions with various pH, carrots, blueberries, red cabbage, red grapes, red onions, tea leaves, 100mL beaker, deionized water, pipettes, well plates, scoopula

DEMO Why do chemistry teachers like to teach about hydroxides?

Calculating pH and pOH

Acids Recall that acids dissociate in water and give off H+ ions HCl H+1 + Cl-1 H2O

[H+] = the hydrogen ion concentration IN MOLARITY pH What is an easy way of representing the concentration of hydrogen ions in a solution? pH (“potential of hydrogen”): a way of expressing the hydrogen ion concentration pH = - log [H+] [H+] = the hydrogen ion concentration IN MOLARITY

Calculating pH [H+] pH 1 1 x 10-3 M 2 1 x 10-5 M 3 1 x 10-7 M 4 Calculate the pH values using the equation pH = - log [H+]. Do you notice a pattern? 3.0 5.0 7.0 9.0 12.0 As the pH value increases, the H+ concentration decreases

The pH Scale As the pH value increases, the H+ concentration decreases As the pH value decreases, the H+ concentration increases

Calculating pH Example pH = - log [H+] What is the pH of a HCl solution in which [H+] = 3.9 x 10-4 M?

[H+] = the hydrogen ion concentration IN MOLARITY Calculating [H+] How do we calculate the hydrogen ion concentration, [H+], if we know the pH? [H+] = 10-pH pH = - log [H+] [H+] = the hydrogen ion concentration IN MOLARITY

Calculating [H+] Example [H+] = 10-pH What is the [H+] of a solution if the pH = 10.8?

Bases Recall that bases dissociate in water and give off OH-1 ions NaOH Na+1 + OH-1 H2O

[OH-] = the hydroxide ion concentration IN MOLARITY pOH Just like with pH… pOH (“potential of hydroxide”): a way of expressing the hydroxide ion concentration (the OH-) pOH = - log [OH-] [OH-] = the hydroxide ion concentration IN MOLARITY Just like with [H+]: [OH-] = 10-pOH The only way to go between H and OH: pH + pOH = 14

Example #1 What is the pOH of a solution if the [OH-] = 3.5 x 10-9 M?

Example #2 What is the pH of a solution if the [OH-] = 0.00059 M?

Example #3 What is the hydrogen ion concentration of a solution if the pOH is equal to 11.2?

Acid-Base Neutralization Reactions

Neutralization Reactions Remember double replacement reactions? HCl + NaOH → ____ + ____ To write balanced reaction: 1. Circle any polyatomic ions 2. Label charges 3. Write products – make charges cancel! 4. Balance using coefficients

Neutralization Reactions Remember double replacement reactions? HCl + NaOH → ____ + ____ HCl + NaOH → NaCl + HOH All neutralization reactions will have this format… Acid + Base  Salt + water (H2O)

Neutralization Reactions Practice #1 Name the acid and the base: HCl + Ca(OH)2  hydrochloric acid calcium hydroxide Complete and balance the neutralization reaction: HCl + Ca(OH)2  _____ + _____ 2HCl + Ca(OH)2  CaCl2 + 2H2O Remember: 1. Circle any polyatomic ions 2. Label charges 3. Write products – make charges cancel! 4. Balance using coefficients

Neutralization Reactions Practice #2 Name the acid and the base: H2SO4 + NaOH  sulfuric acid sodium hydroxide Complete and balance the neutralization reaction: H2SO4 + NaOH  _____ + _____ H2SO4 + 2NaOH  Na2SO4 + 2H2O Remember: 1. Circle any polyatomic ions 2. Label charges 3. Write products – make charges cancel! 4. Balance using coefficients

Neutralization Reactions Practice #3 Name the acid and the base: H2SO3 + NH4OH  sulfurous acid ammonium hydroxide Complete and balance the neutralization reaction: H2SO3 + NH4OH  _____ + _____ H2SO3 + 2NH4OH  (NH4)2SO3 + 2H2O Remember: 1. Circle any polyatomic ions 2. Label charges 3. Write products – make charges cancel! 4. Balance using coefficients

Neutralization Practice

Neutralization Reactions Practice #4 Name the acid and the base: H3PO4 + LiOH  phosphoric acid lithium hydroxide Complete and balance the neutralization reaction: H3PO4 + LiOH  _____ + _____ H3PO4 + 3LiOH  Li3PO4 + 3H2O Remember: 1. Circle any polyatomic ions 2. Label charges 3. Write products – make charges cancel! 4. Balance using coefficients

Acid-Base Titrations

Titrations Titration: adding a known amount of solution of known concentration to a solution with an unknown concentration Goal: To determine the unknown concentration of a solution

Titrations Endpoint: the point of neutralization in a titration How do we know we reached the endpoint in a titration? We use an indicator and look for a color change! http://www.youtube.com/watch?v=g8jdCWC10vQ

To solve this problem, we need to use the box method! Titration Example A 2.5 L solution of H2SO4 is completely neutralized by 0.5 L of 1.0 M NaOH. What is the concentration of the H2SO4 solution? In buret: 1.0 M NaOH To solve this problem, we need to use the box method! In Erlenmeyer flask: ? M H2SO4

A 2. 5 L solution of H2SO4 is completely neutralized by 0. 5 L of 1 A 2.5 L solution of H2SO4 is completely neutralized by 0.5 L of 1.0 M NaOH. What is the concentration of the H2SO4 solution? Step 1: Write the balanced neutralization equation. H2SO4 + 2 NaOH  Na2SO4 + 2 H2O

H2SO4 + 2 NaOH  Na2SO4 + 2 H2O 0.25 mol 0.5 mol 0.10 M 1.0 M 2.5 L A 2.5 L solution of H2SO4 is completely neutralized by 0.5 L of 1.0 M NaOH. What is the concentration of the H2SO4 solution? Step 2: Draw the box, fill in known information, and calculate missing information. H2SO4 + 2 NaOH  Na2SO4 + 2 H2O x 1/2 Multiply by molar ratio Moles (mol) Molarity (M) Liters (L) 0.25 mol 0.5 mol 0.10 M 1.0 M Moving up = multiply 2.5 L 0.5 L Moving down = divide

Titration Practice - #1 on WS 30 mL of 0.10 M NaOH is used to completely neutralize 25.0 mL of HCl. Determine the concentration of the acid. Moles (mol) Molarity (M) Liters (L)

HCl Titration Lab – Analysis Questions Work with your partner to complete questions 3-5 on your lab…

Titration Practice #1 A 1.5 L solution of HCl is completely neutralized by 2.0 L of 0.5 M Al(OH)3. What is the concentration of the HCl solution? Moles (mol) Molarity (M) Liters (L)

Titration Practice #2 A 25 mL solution of H2SO4 is completely neutralized by 6.5 mL of 1.0 M NaOH. What is the concentration of the H2SO4 solution? Moles (mol) Molarity (M) Liters (L)