Acids and Bases

Characteristics of Acids  Sour taste (aqueous solutions)  Change the color of indicators  pH paper: reds and oranges  Litmus paper: red  Clear in phenolphthalein  Bromthymol blue - yellow  Phenol red-yellow  Some react with active metals and release hydrogen gas  Acids react with bases to form salts (neutralization reactions)  Acids conduct electricity.  pH 1-7  Strong and weak acids

Uses of Acids  Acetic Acid (CH 3 COOH)= Vinegar  Citric Acid (C 6 H 8 O 7 ) = lemons, limes, & oranges. It is in many sour candies such as lemonhead & sour patch.  Ascorbic acid (C 6 H 8 O 6 ) (= Vitamin C which your body needs to function.  Sulfuric acid (H 2 SO 4 ) is used in the production of fertilizers, steel, paints, and plastics.  Acetylsalicylic acid ((C 9 H 8 O 4 )-aspirin  HCl- used in our stomach to digest food.

Characteristics of Bases  Taste bitter (aqueous solutions)  Change the colors of indicators  pH paper –green and blue  Litmus paper blue  Phenolphthalein-pink  Bromthymol blue-blue  Phenol red-pink  Dilute aqueous solutions feel slippery  Bases react with acids to form salts (neutralization reactions)  Bases conduct electricity.  pH 8-14

Uses of bases  Bases give soaps, ammonia, and many other cleaning products some of their useful properties.  The OH- ions interact strongly with certain substances, such as dirt and grease.  Chalk and oven cleaner are examples of familiar products that contain bases.  Your blood is a slightly basic solution (7.4)

Common Acids  Fruit Juices  Sulfuric acid  Used in petroleum refineries and the manufacture of fertilizer. Dehydrates water from compounds.  Nitric acid  Stains proteins yellow, used in explosives.  Phosphoric acid  Used in the manufacture of fertilizer and animal feed.  Hydrochloric acid  Removes impurities from metal, digests food in stomach  Acetic acid  Used to make vinegar and as a fungicide.  Carbonic acid  Found in the blood as a buffer (maintains pH)

Common Bases  Milk of Magnesia  Neutralize acid in the stomach and maintain pH  Blood  Transports oxygen and nutrients  Drain Cleaner  Loosen debris and dissolve substances  Bleach  Cleaner  Ammonia  Cleaner  *Using ammonia and bleach together releases toxic fumes!

3 Types of Acids and Bases Arrhenius Model  Acids-contain H and donate and H + to solution.  Bases-contain OH and donate OH - to solution.  Examples  Acids: HF, HI, HCl, H 2 O, HBr, H 2 SO 4, H 3 PO 4  Bases: NaOH, Ca(OH) 2, KOH, H 2 O Bronsted- Lowry  Acids- compounds that donate a proton (H+)  Bases-compounds that accept a proton (H+)  Examples  Acids: HCl, HF, HI  Bases: NH 3, H 2 O Lewis: bases donate electron pair (NH 3 ) and acids accept electron pairs (don’t need to have hydrogen!

Misc.  Acidic solutions  Solutions with more H+ than OH-  Basic solutions  Solutions with more OH- than H+  Conjugate acid  The species that results when a base accepts a proton  Conjugate base  The species that results when an acid loses a proton.  Amphoteric  A substance that acts as both an acid or a base (water).

Conjugate Acid/Base Pairs  Acid + Base  Conjugate Acid + Conjugate Base  H 2 SO 4 + H 2 O  H 3 O + + HSO 4 -  H 3 PO 4 + H 2 O  H 3 O + + H 2 PO 4 -  Write the acid….+ water  H 3 O + + conjugate base

Strong Vs. Weak  Strong  The entire sample of Strong acids and bases completely dissociate when dissolved. Ex. Hydrobromic, hydrochloric, nitric….  Weak  Weak acids and bases do not completely dissociate when dissolved. Some of the sample is still together as an entire compound. (hydrosulfuric, hypochlorous, carbonic….  *We will be working with strong acids and bases in problem sets.

Ionization Constant-to what degree will a substance produce ions in water? Ka  [products]/[reactants]  DO NOT WRITE LIQUIDS!  The smaller the number the WEAKER the acid. Kb  [products]/[reactants]  DO NOT WRITE LIQUIDS!  The smaller the number the WEAKER the base.

pH Scale  0-14 Based on a Scale of 10  A change from pH 3 to 2 means 10X more H 3 O +  A change from pH 3 to 1 means 100x more H 3 O +  “power of Hydrogen”  [H 3 O + ] of 10 0 to  Acids 0-7  Neutral 7  Bases 7-14  pH = - log [H 3 O + ]  pOH = - log [OH-]

Ionization of Water  [H 3 O + ]= hydronium ions  [OH-] = hydroxide ions  H 2 O(l) + H 2 O(l)  H 3 O + + OH -  Water ionizes, therefore it has a pH  pH = - log [H 3 O + ]  At 25 ○ C [H 3 O + ] = 1.0 x M  At 25 ○ C [OH-] = 1.0 x M  [H 3 O + ][OH-] = 1.0 x M

Reactions with Acids and Bases  A reaction between an acid and a base is called neutralization. An acid-base mixture is not as acidic or basic as the individual starting solutions.

Neutralization reactions make SALTS

Types of Salts  Acidic  Strong Acid + Weak Base  Turn litmus paper red  Basic  Weak Acid + Strong Base  Turn litmus paper blue  Neutral  Strong Acid + Strong Base  Turn red litmus red, and blue litmus blue

[H 3 O + ][OH-] = 1.0 x M  Acidic solutions [H 3 O + ] > [OH-]  A pH of 4 means that [H 3 O + ] = 1.0 x (more)  This means the [OH-] = 1.0 x (less)  Basic solutions [H 3 O + ] < [OH-]  A pH of 10 means that [H 3 O + ] = 1.0 x (less)  This means the [OH-] = 1.0 x (more)

Formulas to Remember  [H 3 O + ][OH-] = 1.0 x M  pH = - log [H 3 O + ]  [H 3 O + ] = antilog (-pH)  Also written as [H 3 O + ] = 10 -ph

Calculating pH from [H 3 O + ]  What is the pH of a 1.0 x M NaOH solution?  NaOH  Na + + OH -  1.0 x M NaOH = 1.0 x M OH-  [H 3 O + ]= 1.0 x M = 1.0 x M 1.0 x M  pH = - log [ 1.0 x ]  pH = 11  Conversely then, the pOH = 3

Calculating Concentrations from pH and pOH  pH = -log [H 3 O + ]  Log [H 3 O + ] = -pH  [H 3 O + ] = antilog (-pH)  [H 3 O + ] = 10 -pH  Determine the [H 3 O + ] of an aqueous solution that has a pH of 4.0.  [H 3 O + ] = which is the same as 1 x M

Calculating [H 3 O + ] from [OH-]  NaOH  Na + + OH -  Strong Base= completely dissociates  If this is a 1.0 x M solution then…  1.0 x mol NaOH x 1 mol OH- = 1.0 x mol OH  L solution 1 mol NaOH L solution  Because [H 3 O + ][OH-] = 1.0 x M [H 3 O + ]= 1.0 x M = 1.0 x M 1.0 x M

Calculating [OH - ] from [H 3 O + ]  HCl  H + + Cl -  Strong Acid= completely dissociates  If this is a 2.0 x M solution then…  2.0 x mol HCl x 1 mol H+ = 2.0 x mol H  L solution 1 mol HCl L solution  Because [H 3 O + ][OH-] = 1.0 x M  [OH - ]= 1.0 x M = 5.0 x M 2.0 x M

Comparisons Neutral[H 3 O + ] = [OH-] pH = pOH [H 3 O + ] = [OH-]= 1.0 x pH = pOH = 7 Acidic[H 3 O + ] > [OH-] pH<pOH [H 3 O + ] > 1.0 x [OH-] < 1.0 x pH< 7 pOH>7 Basic[H 3 O + ] < [OH-] pH>pOH [H 3 O + ] < 1.0 x [OH-] > 1.0 x pH>7 pOH<7

Titration:  A laboratory method for determining the concentration of an unknown acid or base using a neutralization reaction.  A standard solution,(a solution of known concentration), is used.

Equivalence Point  The point at which there are stoichiometrically equivalent amounts of acid and base.  [H+] = [OH-]

Buret Valve

Titration Acid with Phenolphthalein End-Point

Indicators  Indicators are chosen, such that they change colors at the range of the pH of interest.  The solution itself at the end-point may be:  Basic, if the reaction involves a strong base and a weak acid.  Neutral, if the reaction involves a strong acid and a strong base.  Acidic, if the reaction involves a strong acid and a weak base.

Methods of Solving Titration Problems: a) using stoichiometry b) using the titration formula aM a V a =bM b V b.

What is the concentration of HCl if 30.0 mL of 0.10 M NaOH neutralizes 50.0mL HCl? NaOH + HCl  H 2 O + NaCl Hint: Use aM a V a =bM b V b M a = How many moles of HCl were used? Hint: #moles= M a V a, but convert the volume to L( 50mL=0.05L).

A 20.0 mL solution of Sr(OH) 2 is neutralized after 25.0 mL of standard 0.05 M HCl is added. What is the concentration of Sr(OH) 2 ? 2 HCl + Sr(OH) 2  2 H 2 O + SrCl 2

 How many mL of 0.20 M H 3 PO 4 are needed to neutralize 55.0 mL of a 0.10 M solution of NaOH?

 What volume of 0.20M Ca(OH) 2 will neutralize 45.0 mL of a 1M solution of HClO 3 ? 