Acids and Bases Agenda “ the acid test ”“ acid drop ”“ acid rain ” “ put the acid on...
Click here to load reader
-
Upload
hilda-greene -
Category
Documents
-
view
266 -
download
5
Transcript of Acids and Bases Agenda “ the acid test ”“ acid drop ”“ acid rain ” “ put the acid on...
Acids and Bases
Agenda • “the acid test” “acid drop” “acid rain”• “put the acid on” “do acid” “acid head”
• Day 71 – Strong and Weak Acids and Bases Intro• Lesson: • Handouts: 1. Acid/Base Handout • Text: 1. P.462-466, 470-474- Dissociation vs Ionization • Arrhenius and Bronsted-Lowry Definitions of Acids and
Bases • HW: 1. page 475 # 1,2-12•
Properties of acids and bases• Get 8 test tubes. Rinse all tubes well with water. Add acid
to four tubes, base to the other four.• Touch a drop of base to your finger. Record the feel in the
chart (on the next slide). Wash your hands with water. Repeat for acid.
• Use a stirring rod, add base to the litmus and pH papers (for pH paper use a colour key to find a number). Record results. Repeat for acid.
• Into the four base tubes add: a) two drops of phenolphthalein, b) 2 drops of bromothymol, c) a piece of Mg, d) a small scoop of baking soda. Record results. Repeat for acid.
• Clean up (wash tubes, pH/litmus paper in trash).
BubblesNRBaking sodaBubblesNRMagnesium*Yellow*BlueBromothymol
*Cloudy/ white*PinkPhenolphthalein
RedBlueLitmus (blue or red)114pH (# from the key)
Not slipperySlipperyFeel (choose slippery or not slippery)
SourBitterTasteHCl(aq)NaOH(aq)
Observations*Usually, but not always
6
1. Describe the solution in each of the following as: 1) acid 2) base or 3)neutral.
A. ___soda
B. ___soap
C. ___coffee
D. ___ wine
E. ___ water
F. ___ grapefruit
7
Describe each solution as: 1) acid 2) base or 3) neutral.A. _1_ soda
B. _2_ soapC. _1_ coffeeD. _1_ wineE. _3_ water
F. _1_ grapefruit
8
Identify each as characteristic of an A) acid or B) base
____ 1. Sour taste
____ 2. Produces OH- in aqueous solutions
____ 3. Chalky taste
____ 4. Is an electrolyte
____ 5. Produces H+ in aqueous solutions
9
Identify each as a characteristic of an A) acid or B) base
_A_ 1. Sour taste
_B_ 2. Produces OH- in aqueous solutions
_B_ 3. Chalky taste
A, B 4. Is an electrolyte
_A_ 5. Produces H+ in aqueous solutions
Properties of Acids• They taste sour (don’t try this at home).• They can conduct electricity.
– Can be strong or weak electrolytes in aqueous solution
• React with metals to form H2 gas.
• Change the color of indicators (for example: blue litmus turns to red).
• React with bases (metallic hydroxides) to form water and a salt.
Properties of Acids• They have a pH of less than 7 (more on this concept
of pH in a later lesson)
• They react with carbonates and bicarbonates to produce a salt, water, and carbon dioxide gas
• How do you know if a chemical is an acid?– It usually starts with Hydrogen.– HCl, H2SO4, HNO3, etc. (but not water!)
Acids Affect Indicators, by changing their color
Blue litmus paper turns red in contact with an acid (and red paper stays red).
Acids React with Active Metals
Acids react with active metals to form salts and hydrogen gas:
HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)
This is a single-replacement reaction
Acids React with Carbonates and Bicarbonates
HCl + NaHCO3
NaCl + H2O + CO2
Hydrochloric acid + sodium bicarbonate
salt + water + carbon dioxide
An old-time home remedy for relieving an upset stomach
Effects of Acid Rain on Marble(marble is calcium carbonate)
George Washington:BEFORE acid rain
George Washington:AFTER acid rain
Acids Neutralize Bases
HCl + NaOH → NaCl + H2O
-Neutralization reactions ALWAYS produce a salt (which is an ionic compound) and water.
-Of course, it takes the right proportion of acid and base to produce a neutral salt
Sulfuric Acid = H2SO4 Highest volume production of
any chemical in the U.S. (approximately 60 billion pounds/year)
Used in the production of paper
Used in production of fertilizers
Used in petroleum refining; auto batteries
Nitric Acid = HNO3 Used in the production of
fertilizers Used in the production of
explosives Nitric acid is a volatile acid –
its reactive components evaporate easily
Stains proteins yellow (including skin!)
Hydrochloric Acid = HCl Used in the “pickling” of
steel Used to purify magnesium
from sea water Part of gastric juice, it aids in
the digestion of proteins Sold commercially as
Muriatic acid
Phosphoric Acid = H3PO4 A flavoring agent in
sodas (adds “tart”) Used in the
manufacture of detergents
Used in the manufacture of fertilizers
Not a common laboratory reagent
Acetic Acid = HC2H3O2 (also
called Ethanoic Acid, CH3COOH)
Used in the manufacture of plastics
Used in making pharmaceuticals
Acetic acid is the acid that is present in household vinegar
Properties of Bases (metallic hydroxides)
• React with acids to form water and a salt.• Taste bitter.• Feel slippery (don’t try this either).• Can be strong or weak electrolytes in aqueous
solution• Change the color of indicators (red litmus turns
blue).
Examples of Bases(metallic hydroxides)
Sodium hydroxide, NaOH (lye for drain cleaner; soap)
Potassium hydroxide, KOH (alkaline batteries)
Magnesium hydroxide, Mg(OH)2 (Milk of Magnesia)
Calcium hydroxide, Ca(OH)2 (lime; masonry)
Bases Affect Indicators
Red litmus paper turns blue in contact with a base (and blue paper stays blue).
Phenolphthalein turns purple in a base.
Bases have a pH greater than 7
Bases Neutralize Acids
Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl.
2 HCl + Mg(OH)2
MgCl2 + 2 H2O
Magnesium salts can cause diarrhea (thus they are used as a laxative) and may also cause kidney stones.
Acid-Base TheoriesOBJECTIVES:Compare and contrast acids and bases as defined by the theories of:
a) Arrhenius, b) Brønsted-Lowry, and
c) Lewis.
Svante Arrhenius• He was a Swedish chemist (1859-1927), and a
Nobel prize winner in chemistry (1903)• One of the first chemists to explain the chemical
theory of the behavior of acids and bases
Svante Arrhenius (1859-1927)
1. Arrhenius Definition - 1887
• Acids produce hydrogen ions (H1+) in aqueous solution (HCl → H1+ + Cl1-)
• Bases produce hydroxide ions (OH1-) when dissolved in water.
(NaOH → Na1+ + OH1-)• Limited to aqueous solutions.• Only one kind of base (hydroxides)• NH3 (ammonia) could not be an Arrhenius base: no
OH1- produced.
Polyprotic Acids?
• Some compounds have more than one ionizable hydrogen to release
• HNO3 nitric acid - monoprotic
• H2SO4 sulfuric acid - diprotic - 2 H+
• H3PO4 phosphoric acid - triprotic - 3 H+
• Having more than one ionizable hydrogen does not mean stronger!
Acids• Not all compounds that have hydrogen are acids.
Water?
• Also, not all the hydrogen in an acid may be released as ions– only those that have very polar bonds are
ionizable - this is when the hydrogen is joined to a very electronegative element
Arrhenius examples...
• Consider HCl = it is an acid!• What about CH4 (methane)?• O (e.g. H2SO4) was originally thought to cause acidic
properties. Later, H was implicated, but it was still not clear why CH4 was neutral.
• CH3COOH (ethanoic acid, also called acetic acid) - it has 4 hydrogens just like methane does…?
Arrhenius’ theory Limitation
Using Arrhenius’ theory the following would be incorrectly classified as neutral1. Compounds of hydrogen polyatomic ions (NaHCO3(aq))
2.Oxides of metals and non metals (CaO(aq) and CO2(g))
3.Bases other than hydroxides (NH3(aq) and Na2CO3(aq))
4.Acids that do not contain hydrogen (Al(NO3)3(aq))
Revised Arrhenius theory
Ionization
+Cl HH
HO
+H
HH O Cl+
Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H3O+ (hydronium) ions in solution.
The revised Arrhenius theory involves two key ideas not considered by Arrhenius1. Collisions with water molecules2. The nature of hydrogen ions
Agenda
• Day 72 – Conjugate Acids and Bases• Lesson: PPT• Handouts: 1. Acid/Base Handout. 2 Conjugate
Acid& Base Worksheet• Text: 1. [page 386-388 old text
photocopy!]• HW: 1. [P.389 # 18, 19 page 392 # 8, 9, 11 old
text photocopy!]
2. Brønsted-Lowry - 1923• A broader definition than Arrhenius• Acid is hydrogen-ion donor (H+ or proton);
base is hydrogen-ion acceptor.• Acids and bases always come in pairs.• HCl is an acid.
– When it dissolves in water, it gives it’s proton to water.
HCl(g) + H2O(l) ↔ H3O+(aq) + Cl-(aq)
• Water is a base; makes hydronium ion.
Johannes Brønsted Thomas Lowry (1879-1947) (1874-1936) Denmark England
Brønsted-Lowry Theory of Acids & BasesConjugate Acid-Base Pairs
General Equation
Why Ammonia is a Base
Ammonia can be explained as a base by using Brønsted-Lowry:
NH3(aq) + H2O(l) ↔ NH41+(aq) + OH1-
(aq)
Ammonia is the hydrogen ion acceptor (base), andwater is the hydrogen ion donor (acid).
This causes the OH1- concentration to be greater thanin pure water, and the ammonia solution is basic
Acids and bases come in pairs• A “conjugate base” is the remainder of the
original acid, after it donates it’s hydrogen ion
• A “conjugate acid” is the particle formed when the original base gains a hydrogen ion.
• Thus, a conjugate acid-base pair is related by the loss or gain of a single hydrogen ion.
• Chemical Indicators? They are weak acids or bases that have a different color from their original acid and base
Acids and bases come in pairs• General equation is:
HA(aq) + H2O(l) ↔ H3O+(aq) + A-
(aq)
• Acid + Base ↔ Conjugate acid + Conjugate base
• NH3 + H2O ↔ NH41+ + OH1-
base acid c.a. c.b.• HCl + H2O ↔ H3O1+ + Cl1-
acid base c.a. c.b.• Amphoteric – a substance that can act as
both an acid and base- as water shows
When life goes either wayamphoteric (amphiprotic) substances
HCO3-
H2CO3 CO3-2
+ H+ - H+
Acting like a base
Acting like an acid
accepts H+ donates H+
Brønsted-Lowry Theory of Acids & Bases
Brønsted-Lowry Theory of Acids & BasesNotice that water is both an acid & a base = amphoteric
Reversible reaction
Organic Acids (those with carbon)Organic acids all contain the carboxyl group, (-COOH), sometimes several of them. CH3COOH – of the 4 hydrogen, only 1 ionizable
The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.
(due to being bonded to the highly electronegative Oxygen)
Conjugate Acid-Base Pairs
Conjugate Acid- Base Pairs
In other words: When a proton is gained by a Bronsted-Lowry base, the product formed is referred to as the base’s conjugate acid
Conjugate Acid Conjugate BaseH2O (l)
H2O (l)
NH4+
(aq)
HCO3-
OH-(aq)
H3O+(aq)
NH3 (aq)
H2CO3
CO3-2
HCO3-
Practice problemsIdentify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs:
acid base conjugate acidconjugate baseHC2H3O2(aq) + H2O(l) C2H3O2
–(aq) + H3O+(aq)
conjugate acid-base pairs
acidbase conjugate acidconjugate baseOH
–(aq) + HCO3–(aq) CO3
2–(aq) + H2O(l)
conjugate acid-base pairs
acid base conjugate acidconjugate baseHF(aq) + SO3
2–(aq) F–(aq) + HSO3–(aq)
conjugate acid-base pairs
acidbase conjugate acidconjugate baseCO3
2–(aq) + HC2H3O2(aq) C2H3O2–(aq) + HCO3
–(aq)
conjugate acid-base pairs
acid base conjugate acidconjugate baseH3PO4(aq) + OCl
–(aq) H2PO4–(aq) + HOCl(aq)
conjugate acid-base pairs
Answers: question 18(a)
(b)
(c)
acid base conjugate baseconjugate acidHCO3
–(aq) + S2–(aq) HS–(aq) + CO32–(aq)
conjugate acid-base pairs
baseacid conjugate acidconjugate baseH2CO3(aq) + OH
–(aq) HCO3–(aq) + H2O(l)
conjugate acid-base pairs
acid base conjugate acidconjugate baseH3O+(aq) + HSO3
–(aq) H2O(l) + H2SO3(aq)
conjugate acid-base pairs
8a)
8b)
11a)
base acid conjugate baseconjugate acidOH
–(aq) + HSO3–(aq) H2O(l) + SO3
2–(aq)
conjugate acid-base pairs
11b)
What is the conjugate base of the following substances?
a. H2O ________________ b. NH4
+________________ c. HNO2_______________ d. HC2H3O2_________________ What is the conjugate acid of the following
substances?a. HCO3
-__________________ b. H2O____________ c. HPO4
2-____________ d. NH3___________
Strengths of Acids and Bases
• OBJECTIVES:– Define strong acids and weak acids.
StrengthOBJECTIVES: Define strong acids and weak acids.
•Acids and Bases are classified according to the degree to which they ionize in water:
– Strong are completely ionized in aqueous solution; this means they ionize 100 %
– Weak ionize only slightly in aqueous solution
Strength is very different from Concentration
Strength• Strong – means it forms many ions when dissolved
(100 % ionization)
• Mg(OH)2 is a strong base- it falls completely apart (nearly 100% when dissolved). – But, not much dissolves- so it is not
concentrated
HA
Let’s examine the behavior of an acid, HA, in aqueous solution.
What happens to the HA molecules in solution?
HA
H+
A-
Strong Acid
100% dissociation of HA
Would the solution be conductive?
Strong Acid Dissociation (makes 100 % ions)
HA
H+
A-
Weak Acid
Partial dissociation of HA
Would the solution be conductive?
HA
H+
A-
Weak Acid
HA H+ + A-
At any one time, only a fraction of
the molecules are dissociated.
Weak Acid Dissociation(only partially ionizes)
1. Binary or hydrohalic acids – HCl, HBr, and HI “hydro____ic acid” are strong acids. Other binary acids are weak acids (HF and H2S). Although the H-F bond is very polar, the bond is so strong (due to the small F atom) that the acid does not completely ionize.
Strength of ACIDS
2. Oxyacids – contain a polyatomic ion a. strong acids (contain 2 or more oxygen per
hydrogen)HNO3 – nitric from nitrate
H2SO4 - sulfuric from sulfate
HClO4 - perchloric from perchlorate
b. weak acids (acids with l less oxygen than the “ic” ending
HNO2 – nitrous from nitrite
H3PO3 - phosphorous from phosphite
H2SO3 - sulfurous from sulfite
HClO2 - chlorous from chlorite
c. weaker acids (acids with “hypo ous” have less oxygen than the “ous” ending
HNO - hyponitrous H3PO2 - hypophosphorus
HClO - hypochorous
d. Organic acids – have carboxyl group -COOH - usually weak acids
HC2H3O2 - acetic acid
C7H5COOH - benzoic acid
Strength of Bases
Strong Bases: metal hydroxides of Group I and II metals (except Be) that are soluble in water and dissociate (separates into ions) completely in dilute aqueous solutions
Weak Bases: a molecular substance that ionizes only slightly in water to produce an alkaline (basic) solution (ex. NH3)
What is a strong Base?
A base that is completely dissociated in water (highly soluble).
NaOH(s) Na+ + OH-
Strong Bases:
Group 1A metal hydroxides(LiOH, NaOH, KOH,RbOH, CsOH)
Heavy Group 2A metal hydroxides[Ca(OH)2, Sr(OH)2, andBa(OH)2]
For the following identify the acid and the base as strong or weak .
a. Al(OH)3 + HCl
b. Ba(OH)2 + HC2H3O2
c. KOH + H2SO4
d. NH3 + H2O
Weak base Strong acid
Weak acid
Strong acid
Strong base
Strong base
Weak base Weak acid
Strength vs. Concentration• The words concentrated and dilute tell how much
of an acid or base is dissolved in solution - refers to the number of moles of acid or base in a given volume
• The words strong and weak refer to the extent of ionization of an acid or base
• Is a concentrated, weak acid possible?
3. Lewis Acids and Bases• Gilbert Lewis focused on the donation or
acceptance of a pair of electrons during a reaction• Lewis Acid - electron pair acceptor• Lewis Base - electron pair donor• Most general of all 3 definitions; acids don’t even
need hydrogen!
Gilbert Lewis (1875-1946)
Gilbert Lewis (1875-1946)
Summary: Definitions
• Acids – produce H+
• Bases - produce OH-
• Acids – donate H+
• Bases – accept H+
• Acids – accept e- pair• Bases – donate e- pair
Arrehenius
Bronsted-Lowry
Lewis
only in water
any solvent
used in organic chemistry,wider range of substances
Acids BasesArrhenius Acid: donates (or
produces) hydronium ions (H3O+) in water or hydrogen ions (H+) in water
Bronsted-Lowry Acid: donates a proton (H+) in water, H3O+ has an extra H+, if it donated it to another molecule it would be H2O (page 467)
HNO3 + H2O H+ + NO3-
HNO3 + H2O H3O+ + NO3-
HCl + H2O H+ + Cl-
HCl + H2O H3O+ + Cl-
Arrhenius Base: donates (or produces) hydroxide ions (OH-) in water
Bronsted – Lowry Base: accepts a proton in water, OH- needs an extra H+ if it accepts one from another molecule it would be H2O (page 468)
KOH + H2O K+ + OH-
NH3 + H2O NH4+ + OH-
Hydrogen Ions and AcidityOBJECTIVES:•Describe how [H1+] and [OH1-] are related in an aqueous solution.•Classify a solution as neutral, acidic, or basic given the hydrogen-ion or hydroxide-ion concentration. •Convert hydrogen-ion concentrations into pH values and hydroxide-ion concentrations into pOH values.• Describe the purpose of an acid-base indicator.
Agenda
• Day 73 – pH Calculations • Lesson: PPT• Handouts: 1. pH Handout, 2. pH Calculations
Worksheet• Text: 1. [page 368-374 old text
photocopy!]• HW: 1. [page # 371 # 2, 3, 4, 6 old text
photocopy!]
Hydrogen Ions from Water• Water ionizes, and forms ions:
H2O + H2O↔ H3O1+ + OH1-
• Called the “self ionization” of water• Occurs to a very small extent:
[H3O1+ ] = [OH1-] = 1 x 10-7 M
• Since they are equal, a neutral solution results from water
Kw = [H3O1+ ] x [OH1-] = 1 x 10-14 M2
• Kw is called the “ion product constant” for water
Water Equilibrium
H2O + H2O H3O+ + OH-
Does pure water conduct electrical current?
[H3O+][OH-] = 10-14
For pure water: [H3O+] = [OH-] = 10-7M
This is neutrality and at 25oC is a pH = 7.
Water is a very, very, very weak electrolyte.
How are (H3O+) and (OH-) related?
water
Lone Hydrogen ions do not exist by themselves in solution. H+ is always bound to a water molecule to form a hydronium ion
Ion Product Constant• H2O ↔ H3O1+ + OH1-
• Kw is constant in every aqueous solution:
[H3O+] x [OH-] = 1 x 10-14 M2
• If [H3O+] > 10-7 then [OH-] < 10-7
• If [H3O+] < 10-7 then [OH-] > 10-7
• If we know one, other can be determined• If [H3O+] > 10-7 , it is acidic and [OH-] < 10-7
• If [H3O+] < 10-7 , it is basic and [OH-] > 10-7
– Basic solutions also called “alkaline”
The pH concept – from 0 to 14
• pH = pouvoir hydrogene (Fr.) “hydrogen power”• definition: pH = -log[H3O+]
• in neutral pH = -log(1 x 10-7) = 7• in acidic solution [H3O+] > 10-7
• pH < -log(10-7)– pH < 7 (from 0 to 7 is the acid range)– in base, pH > 7 (7 to 14 is base range)
pH Scale [ ] brackets mean concentration or Molarity
The pH scale indicates the hydronium ionconcentration, [H3O+] or molarity, of a solution. (Inother words how many H3O+ ions are in a solution. Ifthere are a lot we assume it is an acid, if there are veryfew it is a base.)
pH
2 3 4 5 6 7 8 9 10 11 12
neutral @ 25oC(H+) = (OH-)
distilled water
acidic(H+) > (OH-)
basic or alkaline(H+) < (OH-)
natural waters pH = 6.5 - 8.5
normal rain (CO2)pH = 5.3 – 5.7
acid rain (NOx, SOx)pH of 4.2 - 4.4 in
0-14 scale for the chemists
fish populationsdrop off pH < 6 and to zero pH < 5
pH Scale
• A change of 1 pH unit represents a tenfold change in the acidity of the solution.
• For example, if one solution has a pH of 1 and a second solution has a pH of 2, the first solution is not twice as acidic as the second—it is ten times more acidic.
Calculating pOH
• pOH = -log [OH-] • [H+] x [OH-] = 1 x 10-14 M2
• pH + pOH = 14• Thus, a solution with a pOH less than 7 is basic; with
a pOH greater than 7 is an acid• Not greatly used like pH is.
pH and Significant Figures
• For pH calculations, the hydrogen ion concentration is usually expressed in scientific notation
• [H1+] = 0.0010 M = 1.0 x 10-3 M, and 0.0010 has 2 significant figures
• the pH = 3.00, with the two numbers to the right of the decimal corresponding to the two significant figures
Example Problems:1. What is the pH of a 0.001M NaOH solution?
1st step: Write a dissociation equation for NaOHNaOH Na + + OH- 0.001mol 0.001molHydroxide will be produced and the [OH-] = 0.001M
2nd step: pOH = -log [0.001] pOH = 3.0 pH = 14.0-3.0 = 11.0
PRACTICE PROBLEM1. What is the molar concentration of hydronium ion in
a solution of pH 8.25?2. What is the pH of a solution that has a molar
concentration of hydronium ion of 9.15 x 10-5M?3. What is the pOH of a solution that has a molar
concentration of hydronium ion of 8.55 x 10-10 M?4. What is the molar concentration of hydronium ion in
a solution of pH 2.45?5. What is the pH of a solution that has a molar
concentration of hydronium ion of 3.75 x 10-9 M?6. What is the pOH of a solution that has a molar
concentration of hydronium ion of 4.99 x 10-4 M?
5.623 x 10-9 M
pH = 4.0
pOH = 4.9
2. What is the pH of a 3.4X10-5M H2SO4 solution?
3. What is the pH of a solution if the pOH = 5?
4. What is the pH of a 10 liter KOH solution if 5.611 grams of KOH were used to prepare the solution?
5. What is the pOH of a 1.1X10-5M HNO3 solution?
6. If the pH of a KOH solution is 10.75, what is the molar concentration of the solution? What is the pOH? What is the [H+]?
The pH of a strong acid cannot be greater than 7. If the acid concentration [H3O+] is less than 1.0X10-7, the water becomes the important source of [H3O+] or [H+] and the pH is 7.00. Just remember to check if you answer is reasonable!
7. What is the pH of a 2.5X10-10M HCl solution? 8. What is the pH of a 1.0X10-11M HNO3 solution?
What is acid rain?
CO2 (g) + H2O H2CO3 H+ + HCO3-
Dissolved carbon dioxide lowers the pH
Atmospheric pollutants from combustion
NO, NO2 + H2O … HNO3
SO2, SO3 + H2O … H2SO4
bothstrong acids
pH < 5.3
105
Db107
Bh
Behavior of oxides in water– Group Abasic amphoteric acidic
3A 4A 5A 6A 7A
1A
2A
8A
Group B
basic: Na2O + H2O 2NaOH (O-2 + H2O 2OH-)
acidic: CO2 + H2O H2CO3
Measuring pH• Why measure pH?
Everyday solutions we use - everything from swimming pools, soil conditions for plants, medical diagnosis, soaps and shampoos, etc.
• Sometimes we can use indicators, other times we might need a pH meter
pH in the Digestive System
• Mouth-pH around 7. Saliva contains amylase, an enzyme which begins to break carbohydrates into sugars.
• Stomach- pH around 2. Proteins are broken down into amino acids by the enzyme pepsin.
• Small intestine-pH around 8. Most digestion ends. Small molecules move to bloodstream toward cells that use them
mouth
esophagus
stomach
small intestine
large intestine
Digestive system
pH
1 2 3 4 5 6 8 9 10 11
The biological view in the human body
gastric juice
urinesalivacerebrospinal fluid
bloodpancreatic juice
bileacidic basic/alkaline
7
How to measure pH with wide-range paper
1. Moisten the pH indicator paper strip with a few drops of solution, by using a stirring rod.
2.Compare the color to the chart on the vial – then read the pH value.
Some of the many pH
Indicators and theirpH range
Acid-Base Indicators• Although useful, there are limitations to indicators:
– usually given for a certain temperature (25 oC), thus may change at different temperatures
– what if the solution already has a color, like paint?
– the ability of the human eye to distinguish colors is limited
Acid-Base Indicators• A pH meter may give more definitive results
– some are large, others portable– works by measuring the voltage between two
electrodes; typically accurate to within 0.01 pH unit of the true pH
– Instruments need to be calibrated
Neutralization Reactions
• OBJECTIVES:– Define the products of an acid-base reaction.– Explain how acid-base titration is used to
calculate the concentration of an acid or a base.
– Explain the concept of equivalence in neutralization reactions.
Agenda
• Day 74 – Acid & Base Titration - Stoichiometry/pH Calculations
• Lesson: PPT• Handouts: 1. Titration Handout 2. Titration
Problems Worksheet • Text: 1. P. 476- 484 -Titration• HW: 1. P. 485 # 1-13
Acid-Base Reactions• Acid + Base → Water + Salt• Properties related to every day:
– antacids depend on neutralization– farmers adjust the soil pH– formation of cave stalactites– human body kidney stones from insoluble salts
Acid – Base reactions
• Each salt listed in this table can be formed by the reaction between an acid and a base.
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:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
H2SO4(aq) + 2KOH(aq) → K2SO4(aq) + 2 H2O(l)
According to the Bronsted-Lowry theory, in a neutralization reaction a proton is transferred form the strongest acid to the strongest base
Acid – Base Reactions
• 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.
Titration- Stoichiometry• Titration is the process of adding a known amount
of solution of known concentration to determine the concentration of another solution
• Remember? - a balanced equation is a mole ratio
• The equivalence point is when the moles of hydronium ions is equal to the moles of hydroxide ions (= neutralized!)
Titration• 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 we use phenolphthalein- because it is
colorless in neutral and acid; turns pink in base
Steps - Neutralization reaction#1. A measured volume of 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.
Neutralization• The solution of known concentration is called the
standard solution– added by using a burette– Figure 1, page 476
• Continue adding until the indicator changes color– called the “end point” of the titration– Go over Sample Problem1 and 2 , page 482
Question: Write the chemical reaction when lithium hydroxide is mixed with carbonic acid.
Step 1: write out the reactantsLiOH(aq) + H2CO3(aq)
Step 2: determine products … H2O and Li1(CO3)2
LiOH(aq) + H2CO3(aq) Li2CO3(aq) + H2O(l) Step 3: balance the equation
2LiOH(aq) + H2CO3(aq) Li2CO3(aq) + 2H2O(l) lithium hydroxide + carbonic acid lithium carbonate + water
Writing neutralization equationsWriting neutralization equationsWhen acids and bases are mixed, a salt forms
NaOH + HCl H2O + NaCl base + acid water + saltCa(OH)2 + H2SO4 2H2O + CaSO4
a) iron(II) hydroxide + phosphoric acidb) Ba(OH)2(aq) + HCl(aq)c) calcium hydroxide + nitric acidd) Al(OH)3(aq) + H2SO4(aq)e) ammonium hydroxide + hydrosulfuric acidf) KOH(aq) + HClO2(aq)
Assignment
Write balanced chemical equations for these neutralization reactions. Under each compound give the correct IUPAC name.
a) 3Fe(OH)2(aq) + 2H3PO4(aq) Fe3(PO4)2(aq) + 6H2O(l) iron(II) hydroxide + phosphoric acid iron (II) phosphate
b) Ba(OH)2(aq) + 2HCl(aq) BaCl2 (aq) + 2H2O(l) barium hydroxide + hydrochloric acid barium chloride
c) Ca(OH)2(aq) + 2HNO3(aq) Ca(NO3)2(aq) + 2H2O(l) calcium hydroxide + nitric acid calcium nitrate
d) 2Al(OH)3(aq) + 3H2SO4(aq) Al2(SO4)3(aq) + 6H2O(l) aluminum hydroxide + sulfuric acid aluminum sulfate
e) 2NH4OH(aq) + H2S(aq) (NH4)2S(aq) + 2H2O(l) ammonium hydroxide+ hydrosulfuric acid ammonium sulfide
f) KOH(aq) + HClO2(aq) KClO2(aq) + H2O(l) potassium hydroxide + chlorous acid potassium chlorite
TITRATION- MAVA = MBVB
Sample Problem: Suppose 75.00 mL of hydrochloric acid was required toneutralize 22.50 mL of 0.52 M NaOH. What is themolarity ( concentration) of the acid?
Mb = 0.773 mol/L
HCl + NaOH H2O + NaClMa Va = Mb Vb rearranges to Ma = Mb Vb / Va
so Ma = (0.52 M) (22.50 mL) / (75.00 mL) = 0.16 M
Now you try:2.If 37.12 mL of 0.843 M HNO3 neutralized 40.50 mL of KOH, what is the molarity of the base?
TITRATION- Sample Problem: If 37.12 mL of 0.543 M LiOH neutralized40.50 mL of H2SO4, what is the molarity of the acid?
2 LiOH + H2SO4 Li2SO4 + 2 H2O
1. First calculate the moles of base:0.03712 L LiOH (0.543 mol/1 L) = 0.0202 mol LiOH2. Next calculate the moles of acid:0.0202 mol LiOH (1 mol H2SO4 / 2 mol LiOH)= 0.0101 mol
H2SO4
3. Last calculate the Molarity: Ma = n/V = 0.010 mol H2SO4 / 0.4050 L = 0.248 M
Now you try it: If 20.42 mL of Ba(OH)2 solution was used to titrate29.26 mL of 0.430 M HCl, what is the molarity of the bariumhydroxide solution?
Mb = 0.308 mol/L
Titration problems1. What volume of 0.10 mol/L NaOH is needed
to neutralize 25.0 mL of 0.15 mol/L H3PO4?
2. 25.0 mL of HCl(aq) was neutralized by 40.0 mL of 0.10 mol/L Ca(OH)2 solution. What was the concentration of HCl?
3. A truck carrying sulfuric acid is in an accident. A laboratory analyzes a sample of the spilled acid and finds that 20 mL of acid is neutral-ized by 60 mL of 4.0 mol/L NaOH solution. What is the concentration of the acid?
4. What volume of 1.50 mol/L H2S will neutral-ize a solution containing 32.0 g NaOH?
Titration problems1. (3)(0.15 M)(0.0250 L) = (1)(0.10 M)(VB)
VB= (3)(0.15 M)(0.0250 L) / (1)(0.10 M) = 0.11 L
2. (1)(MA)(0.0250 L) = (2)(0.10 M)(0.040 L)
MA= (2)(0.10 M)(0.040 L) / (1)(0.0250 L) = 0.32 M
3. Sulfuric acid = H2SO4
(2)(MA)(0.020 L) = (1)(4.0 mol/L)(0.060 L)
MA = (1)(4.0 M)(0.060 L) / (2)(0.020 L) = 6.0 M
4. mol NaOH = 32.0 g x 1 mol/40.00 g = 0.800 (2)(1.50 mol/L)(VA) = (1)(0.800 mol)
VA= (1)(0.800 mol) / (2)(1.50 mol/L) = 0.267 L
Molarity and Titration• A student finds that 23.54 mL of a 0.122 M
NaOH solution is required to titrate a 30.00-mL sample of hydr acid solution. What is the molarity of the acid?
• A student finds that 37.80 mL of a 0.4052 M NaHCO3 solution is required to titrate a 20.00-mL sample of sulfuric acid solution. What is the molarity of the acid?
• The reaction equation is:H2SO4 + 2 NaHCO3 → Na2SO4 + 2 H2O + 2 CO2
1. How many milliliters of 1.25 M LiOH must be added to neutralize 34.7 mL of 0.389 M HNO3?
2. What mass of Sr(OH)2 will be required to neutralize 19.54 mL of 0.00850 M HBr solution?
3.How many mL of 0.998 M H2SO4 must be added to neutralize 47.9 mL of 1.233 M KOH?
4. How many milliliters of 1.25 M LiOH must be added to neutralize 34.7 mL of 0.389 M HNO3?
5. What mass of Sr(OH)2 will be required to neutralize 19.54 mL of 0.00850 M HBr solution?
6. How many mL of 0.998 M H2SO4 must be added to neutralize 47.9 mL of 1.233 M KOH?
7. How many milliliters of 0.75 M KOH must be added to neutralize 50.0 mL of 2.50 M HCl
10.8 mL
0.0101 g
29.6 mL
10.8 mL
0.0101 g
29.6 mL