Ch. 18/19

Properties of Acids þ Formulas begin with “H” (HCl) þ React with metals to produce hydrogen gas þ Turns blue litmus paper to red þ “Blue to Red A-CID” þ Conduct electricity in water –Electrolytes þ React with bases to form a salt and water þ Taste sour þ pH is less than 7

Common Acids Sulfuric AcidH 2 SO 4 Nitric AcidHNO 3 Phosphoric AcidH 3 PO 4 Hydrochloric AcidHCl Acetic AcidCH 3 COOH Carbonic Acid H 2 CO 3 Battery acid Used to make fertilizers and explosives Food flavoring Stomach & pool acid In Vinegar Carbonated water

Some Properties of Bases  Formulas end in OH -  Turns red litmus paper to blue “Basic Blue”  Are electrolytes  React with acids to form salts and water  Feel soapy, slippery  pH greater than 7  Taste bitter, chalky

Some Common Bases NaOHsodium hydroxide lye KOHpotassium hydroxide liquid soap Ba(OH) 2 barium hydroxidestabilizer for plastics Mg(OH) 2 magnesium hydroxide Milk of magnesia Al(OH) 3 aluminum hydroxide Maalox (antacid) Al(OH) 3 aluminum hydroxide Maalox (antacid)

Self-Ionization of Water As you know, water molecules are very polar, they constantly move, & collide with each other. Sometimes, when they hit, H + ’s are transferred from one molecule to another forming hydroxide ions (-OH -) & hydronium ions (H 3 O + ) H 2 O + H 2 O  H 3 O + + OH -

Self-Ionization of Water

In pure water: [H 3 O + ] = 1 x M and [OH - ] = 1 x M K w = [H 3 O + ][OH - ] K w = (1 x M)(1 x M) = 1 x M 2 K w = ion product constant for water If [H 3 O + ] > then [OH - ] < If [H 3 O + ] If we know one, we can determine the other. Ex. If [H 3 O + ] = what’s the [OH - ] ? K w = [H 3 O + ][OH - ] so … [OH - ] = K w / [H 3 O + ] [OH - ] = 1 x M 2 = 1 x (1 x M) Inverse Proportion!

VERY HANDY TIP!!! *if the 1st factor is a 1, just subtract the exponent from -14 ! - 14 – - 4 = - 10 So, [OH - ] = Ex. If [OH - ] = what’s the [H 3 O + ] ? Ans Ex. If [H 3 O + ] = what’s the [OH - ] ? Ans

If we add something to water to make the [H+] > (and [OH-] < ) The Solution is Acidic If [H+] ) The Solution is Basic Ex. If [OH - ] = M, what’s the [H 3 O + ] ? Is it acidic, basic, or neutral? Ans. [H 3 O + ] = 1 x M Basic Scientists don’t like working with sci. notation any more than you do, so…

Soren Sorensen ( ) pH Scale

The pH Scale Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic Each pH unit is 10 times as large as the previous one A change of 2 pH units means 100 times more basic or acidic x10x pH scale ranges from pH 7 is neutral; pH >7 is Basic pH < 7 is Acidic

Calculating pH & pOH pH = -log [H 3 O + ] Relationship between pH and pOH pH + pOH = 14 Finding [H 3 O + ], [OH - ] from pH, pOH [H 3 O + ] = 10 -pH [OH - ] = 10 -pOH pOH = -log [OH-]

Calculating pH pH = -log [H 3 O + ] Ex. If [H 3 O + ] = 1 x M pH = -log (1 x ) pH = -((log 1) + (log )) pH = - (0 + -5) pH = 5 BIG HINT!!! If the first factor is a one, the pH is just the positive exponent! So… what is the pH of a solution with a [H 3 O + ] = 1 x QUICK!!!! That’s Right! 6 is it acidic, basic, or neutral? acidic

What if the first exponent isn’t a one?! Ans: 4.2 You will need the log button on your calculator! Q: What is the pH if [H + ]= 6.3 x 10 –5 ? pH = – log [H + ] = - log (6.3 x 10 –5 ) What if you’re given pH & asked to find [H 3 O + ]? Ex. What is the [H 3 O + ] of a solution with a pH of 9? If the pH is a whole number, just use it as the negative exponent! So… [H 3 O + ] = 1 x M

What if you’re given a pH that is not a whole number! - pH 2 nd log 10 x (antilog) Ex. Determine the hydronium ion concentration of a solution with a pH of 4.6. *You can check your answer by working backwards. pH = - log [H + ] pH = - log [2.51x10 -5 M] pH = 4.6 *if it was 1 x the pH would be 5 – so, is it reasonable ? or 10 -pH = [H+] = 2.51 x M

Q: What is the [H+] if pH = 7.4? [H+] = 10 –pH mol/L [H+] = 10 –7.4 mol/L 3.98 x 10 –8 M

pH Calculations pH pOH [H 3 O + ] [OH - ] pH + pOH = 14 pH = -log[H 3 O + ] [H 3 O + ] = 10 -pH pOH = -log[OH - ] [OH - ] = 10 -pOH [H 3 O + ] [OH - ] = 1 x10 -14

pH Scale

ACID – BASE THEORIES There are 3 main acid-base theories. We will look at the two earliest ones! (In chronological order) More recent theories do not negate earlier ones – they just expand on them so they include more substances!

Svante Arrhenius Arrhenius Acids - produce hydrogen ions in aqueous solution. HCl H + + Cl - Arrhenius Bases - produce hydroxide ions when dissolved in water. KOH K + + OH -

Polyprotic Acids Some compounds have more than 1 ionizable hydrogen. HNO 3 nitric acid - monoprotic - 1 H + H 2 SO 4 sulfuric acid - diprotic - 2 H + H 3 PO 4 phosphoric acid - triprotic – 3 H +

Bronsted-Lowry Acids & Bases A B-L Acid is a proton (H + ) donor A B-L Base is a proton (H + ) acceptor. These acids and bases always come in pairs in an entire equation! Ex. HCl(g) + H 2 O(l) H 3 O + + Cl - acid base

NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) Identify the acid & the base in this equation 1.Find the “look-a-likes” & connect them 2. Decide what happens to each reactant (Lose an H? Gain an H?) Acid Base 3. Do the same for the products. These are labeled the “conjugates” base acid conjugate baseconjugate acid

What do you notice about water in the two examples we just did? that’s right! In the first, it acted like a base, and in the second it acted like an acid! (How fickle!) Water is Amphoteric –it can act as either an acid or a base depending on what you put it with!

Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: acidbase conjugate acidconjugate base HC 2 H 3 O 2 (aq) + H 2 O (l)  C 2 H 3 O 2 – (aq) + H 3 O + (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base OH – (aq) + HCO 3 – (aq)  CO 3 2– (aq) + H 2 O (l) conjugate acid-base pairs

acidbase conjugate acidconjugate base HF (aq) + SO 3 2– (aq)  F – (aq) + HSO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base CO 3 2– (aq) + HC 2 H 3 O 2 (aq)  C 2 H 3 O 2 – (aq) + HCO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base H 3 PO 4 (aq) + OCl – (aq)  H 2 PO 4 – (aq) + HOCl (aq) conjugate acid-base pairs (a) (b) (c)

Acid-Base Reactions Neutralization Reaction - a reaction in which an acid and a base react in an aqueous solution to produce a salt and water: Acid + Base Water + Salt HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) H 2 SO 4(aq) + 2KOH (aq) K 2 SO 4(aq) + 2 H 2 O (l)

Question: Write the chemical reaction when lithium hydroxide is mixed with carbonic acid. Step 1: write out the reactants LiOH (aq) + H 2 CO 3 (aq)  Step 2: determine products -H 2 O and Li +1 (CO 3 ) -2 LiOH (aq) + H 2 CO 3 (aq)  Li 2 CO 3 (aq) + H 2 O (l) Step 3: balance the equation 2LiOH (aq) + H 2 CO 3 (aq)  Li 2 CO 3 (aq) + 2H 2 O (l) lithium hydroxide + carbonic acid  lithium carbonate + water Writing neutralization equations NaOH + HCl  H 2 O + NaCl Ca(OH) 2 + H 2 SO 4  2H 2 O + CaSO 4

Strengths of Acids & Bases (strong does not mean concentrated!) Strong acids and bases completely ionize in solution (about 99%) Ex. Strong acids: HCl, H 2 SO 4, HNO 3 Weak acids and bases don’t completely ionize. (about 1%) Ex. Weak base: NH 3 (NH 4 OH)

Representation of the behavior of acids of different strengths in aqueous solution.

Marieb, Fig 26.11

Salt Hydrolysis We saw that a salt, for example NaCl, is formed in a neutralization reaction. the anion of the salt comes from the acid Cl - from HCl and the cation comes from the base Na + from NaOH some salt solutions are neutral; some are acidic or basic Salt hydrolysis- salt reacts with water to produce an acidic or basic solution

Salt Hydrolysis To see if the resulting salt is acidic or basic, check the “parent” acid and base that formed it: 1. NaCl HCl + NaOH 2. (NH 4 ) 2 SO 4 H 2 SO 4 + NH 4 OH 3. KC 2 H 3 O 2 HC 2 H 3 O 2 + KOH

Hydrolyzing salts usually made from: strong acid + weak base = slightly acidic weak acid + strong base = slightly basic (Whose the dominant parent?!!) strong acid + strong base = neutral NaCl OH H

Titration is the process of adding a known amount of solution of known concentration to determine the concentration of another solution

The concentration of acid (or base) in solution can be determined by performing a neutralization reaction An indicator is used to show when neutralization has occurred Often use phenolphthalein- colorless in neutral and acid; turns pink in base

#1. A measured volume of an acid of unknown concentration is added to a flask #2. Several drops of indicator added #3. A base of known concentration is slowly added, until the indicator changes color; measure the volume

The solution of known concentration is called the standard solution added by using a buret Continue adding until the indicator changes color called the “end point” of the titration

TitrationTitration 1. Add solution from the buret. 2. Reagent (base) reacts with compound (acid) in solution in the flask. 3.Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base) This is called NEUTRALIZATION. This is called NEUTRALIZATION. Simulation

Setup for titrating an acid with a base

pH testing There are several ways to test pHThere are several ways to test pH Blue litmus paper (red = acid)Blue litmus paper (red = acid) Red litmus paper (blue = basic)Red litmus paper (blue = basic) pH paper (multi-colored)pH paper (multi-colored) pH meter (7 is neutral, 7 base)pH meter (7 is neutral, 7 base) Universal indicator (multi-colored)Universal indicator (multi-colored) Indicators like phenolphthaleinIndicators like phenolphthalein Natural indicators like red cabbage, radishesNatural indicators like red cabbage, radishes

Paper testing Paper tests like litmus paper and pH paperPaper tests like litmus paper and pH paper Put a stirring rod into the solution and stir.Put a stirring rod into the solution and stir. Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paperTake the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper Read anRead an d record the color change. Note what the color indicates.d record the color change. Note what the color indicates. You should only use a small portion of the paper. You can use one piece of paper for several tests.You should only use a small portion of the paper. You can use one piece of paper for several tests.