Antacids: 2B This unit will introduce the chemistry needed to understand how antacids work  Section 2.4: Defining & Naming Acids & Bases  Section 2.5a Characteristics of Acids & Bases  Sections 2.5b pH calculations  Section 2.5c Acid-Base Titrations

Section 2.4 We need to know how acids behave when talking about ant-acids!

What is an Acid? – Arrhenius Definition A substance that produces hydrogen ions (H +1 ) when dissolved in water. H +1 immediately reacts with water to make the hydronium ion, H 3 O +1 H O H water H +1 H O H H

How do Acids produce Hydronium? H O H H - water acid Hydrogen cation with some anion

How do Acids produce Hydronium? H O H H - +1

How do Acids produce Hydronium? H O H H +1 - Hydronium ion Anion

How to Identify an Acid Look for a hydrogen ion, “H + ” as the first element in an aqueous covalent compound. H 2 SO 4 (aq) HCl (aq) H 2 CO 3 (aq) HNO 3 (aq)

These compounds have to :  Start with “H” (more than 1 “H” is OK, too).  Do not contain oxygen To name these compounds:  Use “hydro____ic acid”  Fill in the blank with the root of the anion’s name Naming Binary Acids: Non-Oxygen Acids

Example #1 HBr (aq)

Hydrogen cation Bromine It’s an acid No oxygen Use “hydro___ic” Hydrobromic acid

These compounds have:  Start with “H” (more than 1 “H” is OK, too).  Must contain oxygen To name these compounds:  Use “___ic acids” for “-ate” anions  Use “___ous acids” for “-ite” anions Naming Oxyacids: contain oxygen Do not use “hydro” with these…the word “acid” is how you know it begins with hydrogen, not “hydro-”

Examples: 1 st 2 rows in notes (1-4)

Example #5 HNO 2(aq)

Hydrogen cation nitrite ion It’s an acid “-ite” ion Use “___ous” acid HNO 2(aq) Nitrous acid

Example #6 HC 2 H 3 O 2(aq)

Hydrogen cation acetate ion It’s an acid “-ate” ion Use “___ic” HC 2 H 3 O 2(aq) acetic acid

Self Check Example: Write the name for the following acids HF H2SH2S H 3 PO 4

Answers Hydrofluoric acid Hydrosulfuric acid Phosphoric acid Example: Write the name for the following acids HF H 2 S H 3 PO 4

To write these formulas:  Write the cation, H +1  Write the anion symbol and charge  Balance the charges by adding the appropriate subscript to the hydrogen cation OR Criss Cross Method Writing the chemical formula for “Hydro-” acids

Example #4 Hydrobromic acid

Hydrogen cation Does not contain oxygen H +1 Br -1

Hydrobromic acid Hydrogen cation Does not contain oxygen H +1 Br -1 HBr H +1 Br = 0 The compound is neutral. Subscripts are not needed

To write these formulas:  Write the cation H +1  If it is an “-ic” acid, determine the polyatomic ion ending in “-ate”  If it is an “-ous” acid, determine the polyatomic ion ending in “-ite”  Add subscript to the hydrogen cation to balance charges OR use Criss Cross Method Writing chemical formulas for “Oxyacids”

Example #5 Carbonic acid

Hydrogen cation From the “___ate” anion H +1 CO 3 -2

Carbonic acid Hydrogen cation From the “___ate” anion H +1 CO 3 -2 H 2 CO 3 H + CO = -1 H + H + CO = 0

Example #6 Chlorous acid

chlorous acid Hydrogen cation From the “___ite” anion H +1 ClO 2 -1

Chlorous acid Hydrogen cation From the “___ite” anion H +1 ClO 2 -1 HClO 2 H + ClO = 0

Self Check Example: Write the formula for the following acids Phosphorous acid Hydroiodic acid

Phosphorous acid Hydroiodic acid Answers H 3 PO 3 HI Example: Write the formula for the following acids

You Really Only Need to Know These Acids! Memorize them! Hydrochloric acid HCl Sulfuric acid H 2 SO 4 Carbonic acid H 2 CO 3 Nitric acid HNO 3 Acetic acid HC 2 H 3 O 2

What is a Base? – Arrhenius Definition A substance that produces hydroxide ions, OH -1 in water H 2 O NaOH (s)  Na +1 (aq) + OH -1 (aq) H O Hydroxide Ion H O H water O Na H +1

How to Identify a Base Look for an ionic compound that has a metal paired with the hydroxide ion, “OH - ” OR Look for the ammonia molecule NaOH Ca(OH) 2 NH 3 **Do not assume all compounds ending in OH are bases: CH 3 OH is not a base but an alcohol

Follow the rules for ionic compounds. The most common exception to this is ammonia, NH 3  NH 3 (ammonia) is a base even though it doesn’t contain “- OH” as the anion Naming & Writing Formulas for Metal Hydroxides

Example #7 NaOH

Sodium Hydroxide Sodium Hydroxide

Self Check Example: Write the formula or name for each Ca(OH) 2 KOH Copper (II) hydroxide Lithium hydroxide

Answers Calcium hydroxide Potassium hydroxide Cu(OH) 2 Mg(OH) 2 Example: Write the formula or name for each Ca(OH) 2 KOH Copper (II) hydroxide Magnesium hydroxide

Another of definition of an ACID: According to Bronsted-Lowry  An acid is a hydrogen (proton) donor  The substance that remains after the hydrogen has been donated is called the conjugate base Example: HCl + H 2 O  H 3 O + + Cl - acid conjugate base

Another definition of a BASE: According to Bronsted-Lowry  A base is a hydrogen (proton) acceptor  The substance that forms after the hydrogen has been accepted is called the conjugate aci Example: NH 3 + H 2 O  OH - + NH 4 + base conjugate acid

Bronsted-Lowry: The Big Picture

Conjugate Acid-Base Pairs ACIDS & BASES WILL ALWAYS BE ON THE REACTANT SIDE CONJUGATE ACIDS & BASES WILL ALWAYS BE ON THE PRODUCT SIDE Practice Problems: Label the acid & base on the left side of the reaction and the conjugate acid & conjugate base on the right side. a) HNO 3 + H 2 O  H 3 O + + NO 3 − ______ ______ ______ ______ b) HCO H 2 O  H 2 CO 3 + OH − _____ ______ ______ ______ acidbaseC.A.C.B. baseacid C.A.C.B.

Section 2.5a:Characteristics & pH We need to know how acids behave when talking about ant-acids!

Characteristics of Acids & Bases BasesAcids Produce H 3 O +1 (hydronium ion) in water Produce OH -1 (hydroxide ion) in water Tastes sour Tastes Bitter React with active metals to form hydrogen gas Feels slippery Both forms ions when dissolved: conducts electricity: They are called ELECTROLYTES Neutralizes a base to form salt and water Neutralizes an acid to form salt and water

Section 2.5

Strength versus Concentration

strong acid – ALL acid molecules separate (dissociate) into [H + ] ions in water; only ions present Examples: HCl, HNO 3, H 2 SO 4 weak acid – Most acid molecules stay together, only a FEW separate into [H + ] ions when in water; few ions present, mostly molecules Examples: HC 2 H 3 O 2 (vinegar), H 2 CO 3

Strong Acid Weak Acid

Strong versus Weak Acids Strong acid Most of the acid molecules have donated the H +1 to water How many hydronium ion – anion pairs can you find? How many intact acid molecules can you find? 3 1

Strong versus Weak Acids + - Weak acid Only a few of the acid molecules have donated the H +1 to water How many hydronium ion – anion pairs can you find? How many intact acid molecules can you find? 1 3

Strong Acids vs. Weak Acids

Concentrated versus Dilute solute solvent DILUTE (low concentration) Very little solute (what’s being dissolved) particles in solution CONCENTRATED (higher concentration) Lots of solute (what’s being dissolved) particles in solution

Combinations of Concentration & Strength Dilute Concentrated A lot of acid/base added & all split into ions Not much acid/base added, but all of what’s there slits into ions A lot of acid/base added, but little splits into ions Not much acid/base added and very little splits into ions Strong Weak

Bases follow the same pattern as acids A common misconception is acids are dangerous but bases are not!  Vinegar is an acid we eat…some of them are safe!  Sodium hydroxide is a very caustic base…not all of them are less harmful than acids!  The stronger and acid or base is & the more concentrated it is), the more dangerous it is for you! Bases Strength & Concentration

Acids and Bases are Electrolytes Acids and bases break apart into ions when dissolved in water Free-floating ions in water conduct electricity Acids & Bases are ELECTROLYTES Strong acids and bases are strong electrolytes - They produce lots of ions Weak acids and bases are weak electrolytes -they don’t produce lots of ions

The pH scale to measure the acidity of a sample The Power of the Hydrogen: pH Acids have a pH that are less than 7.0 Bases have pH values that are more than 7.0 Neutral is considered a pH of 7.0

Indicators change color based on pH  Liquid indicators – phenolphthalein or bromothymol blue Bromothymol Blue: Acid: turns Yellow Base: turns blue Phenolphthalein: Acid: stays clear Base: turns pink pH meters or pH probes  Electronically determine pH and give a read-out Ways to measure pH Acid Base

Indicators change color based on pH  Paper with a liquid indicator on it (pH paper or Litmus paper) pH paper turns a color which matches to a pH number LITMUS PAPER (Mnemomic: See board!) Blue Litmus stays blue in a base but turns pink in an acid Red Litmus stays red in an acid but turns blue in a base Ways to Measure pH

Practice Questions 1. Which of the following is an Arrhenius Acid? a. CuOHb. NH 3 c. HC 2 H 3 O 2 d. CaS 2. Which of the following substances has a bitter taste and slippery feel? a. CH 3 OHb. NH 3 c. HC 2 H 3 O 2 d. K 2 S

Practice Questions 3. Which of the following has a pH of 4? a. NaOHb. SO2 c. baking sodad. H 2 SO 4 4. Which of the following substances will cause red litmus to turn blue? a. NaClb. KOH c. H 3 PO4d. H 2 CO 3

Practice Questions 5. Which of the following will neutralize an acid? a. NaOHb. CH 4 c. CaF 2 d. HNO 2 6. Which of the following substances will increase the number of hydroxide ions in solution? a. Fe 2 O 3 b. H 2 SO 4 c. NH 3 d. H 2 CO 3

Calculating pH pH scale – Logarithmic scale of the acidity of a solution The pH scale uses base “10” pH has no units [ ] = concentration in Molarity The formula for calculating pH The formula for calculating hydronium ion concentration

The “-” in the pH equation Because pH is the negative log of concentration of hydronium, as concentration increases, the pH goes down. The lowest pH is the highest concentration of hydronium ion

What does a “log” scale really mean? pH x more acidic 100x more acidic 1000x more acidic Level of acidity increases Every change of 1 in pH shows a change of 10x in concentration of hydronium

Example The pH of a solution changes from a pH of 5 to a pH of 3. a.Did it increase or decrease in hydrogen ion concentration? b.By what factor did it change?

Example 2 :Calculating pH Example: Find the pH if the concentration of [H 3 O +1 ] is 1.0x M

An example of calculating pH pH = 8.00 Example: Find the pH if the concentration of [H 3 O +1 ] is 1.0 x M

Example 3; Calculating hydronium concentration ( [H 3 O +1 ]) Example: Find the [H 3 O +1 ] if the pH is 5.0

An example of calculating hydronium H 3 O +1 = 1 x M Example: Find the [H 3 O +1 ] if the pH is 5.0

Auto-ionization of Water Water molecules collide spontaneously and will split into ions. This is called auto- ionization H 2 O + H 2 O  H 3 O +1 + OH -1 At 25°C the following is true: [H 3 O +1 ] × [OH -1 ] = 1.0 × M 2

Hydrogen Ion Concentration Values If the hydrogen ion concentration is greater than hydroxide ion, the solution is ACIDIC with a pH < 7 – [H+] > [OH-] or – [H+] > 1.0 x M If the hydrogen ion concentration is less than hydroxide ion, the solution is BASIC with a pH > 7 – [H+] < [OH-] or – [H+] < 1.0 x M If the hydrogen ion concentration is equal to hydroxide ion, the solution is NEUTRAL with a pH = 7 – [H+] = [OH-] = 1.0 x M

Calculating pOH [ ] = concentration in Molarity The formula for calculating pOH The formula for calculating hydroxide ion concentration To relate pH and pOH

Let’s Practice #1 Example: Find the pOH if the concentration of [OH -1 ] is 1.0 × M

Let’s Practice #1 pOH = 5.00 Example: Find the pOH if the concentration of [OH -1 ] is 1.0 × M

Let’s Practice # 2 Example: Find the pOH if the pH is 4.

Let’s Practice #2 Example: Find the pOH if the pH is 4. pOH= 10

Let’s Practice #3 Example: Find the [OH -1 ] if the [H+] is 1.0 x10 -9 M

Let’s Practice #3: 2 ways to do this… 1 st way Example: Find the [OH -1 ] if the [H+] is 1.0 x10 -9 [OH-] = 1.0 x10 -5 M

Let’s Practice #3: 2 ways to do this… 2 nd way Example: Find the [OH -1 ] if the [H+] is 1.0 x10 -9 [OH-] = 1.0 x10 -5 M pH = 9.00 pOH = 14 pOH = 5.00

Let’s Practice #4 Example: What is the pH if the concentration of [OH- ] = 1.0 x M

Let’s Practice #4 pOH = 7 Example: What is the pH if the concentration of [OH-] = 1.0 x pH = 7

Section Section 2.5B Acid- Base Titrations

Titrations—Using Stoichiometry Titration – A technique where the addition of a known volume of a known concentration solution to a known volume of unknown concentration solution to determine the concentration. Use a buret to titrate unknown concentration of solutions.

Titrations—Using Stoichiometry The titrant is the known concentration in the buret and the analyte is the unknown concentration in the flask. Formula: n a M a V a = n b M b V b n a = number of H + in the acid formula n b = number of OH - in the base formula M a = molarity of acid M b = molarity of base V= volume

End Point vs. Equivalence Point Equivalence Point (or Stoichiometric Point) – When there are no reactants left over—they have all been reacted and the solution contains only products -the point where the acid and the base are equal in equal moles moles acid = moles base

Importance of Indicators Always select an indicator that has a pH value close to that of the pH of the equivalence point of the titration. Indicators – Paper or liquid that change color based on pH level. End Point: point at which the indicator in the solution changes color It signals the equivalence point and the stop of the titration

Titration Process

Titration Problem #1 How many liters of 0.10 M NaOH is needed to react with L of 0.25 M HCl?

Titration Problem #2 What is the molarity of a Ca(OH) 2 solution if 30.0 ml of the solution is neutralized by 20.0 ml of a 0.50 M solution of HCl?

Titration Problem #3 What volume of 2.0M solution of NH 4 OH is needed to neutralize 50.0 ml of a 0.50M solution of H 2 SO 4 ?

Titration Curves Shows the changes of pH during a titration Identifies the pH of the equivalence point Strong Base - Strong Acid Weak Base - Strong Acid Strong Base - Weak AcidWeak Base - Weak Acid

Titration curve for Titrating a strong acid with a strong base pH is always = 7 The titration curve graph shows the pH of the equivalence point. Take the vertical region and cut the length in half and then look to what pH value aligns to that point.

Titration curve for Titrating a strong base with an strong acid pH is always = 7

Titration curve for Titrating a weak acid with an strong base pH is >7