some of our favorite foods make our tongue curl up because they are sour. acids and bases
TRANSCRIPT
Some of our favorite foods make our tongue curl up because they are SOUR.
Acids and BasesAcids and Bases
Bitter!
Some foods have a “bite” of their own because they’re somewhat bitter.
WHY?
Acidic/Basic
There is a scientific reason for this:
These foods are either acidic or basic.
Other substances besides foods have these characteristics.
Acids and BasesAcids and BasesChemicals may be classed as acids or bases.
Things that are neither acids nor bases are neutral.
pH measures how acidic or basic a solution is.
AcidsOften taste sour
Strong acids can burn skin & eyes
Strong acids can dissolve metals
Examples:Lemon juiceVinegarCar battery acid (dangerous!)
BasesCan taste bitter, sweetish, or saltyStrong bases can burn skin & eyesBases react more easily with protein than with metal; they are often used for cleaningExamples: Milk Baking soda Soap Drain cleaner (dangerous!)
Some substances are not really an acid or a base: For example, pure water
Acids are easy to recognize as compounds as they begin with the element hydrogen. As with other ionic bonds, acids fall into 2 categories, binary and ternary.
The Nomenclature of The Nomenclature of ACIDSACIDS
Examples of binary acids would include things like:
HF, HI, H2S and HCl
Examples of ternary acids would include things like:
H2SO4 and HNO3
The Nomenclature of The Nomenclature of ACIDSACIDS
Naming of binary acids
Step 1:Name the anion, changing the ending to “-ic”
Step 2: Add the prefix “hydro-”
Step 3: Slap acid on the end
The Nomenclature of The Nomenclature of ACIDSACIDS
Example #1: HFExample #1: HF
The Nomenclature of The Nomenclature of ACIDSACIDS
““fluorine” becomesfluorine” becomes
“ “fluoric” becomesfluoric” becomes“hydrofluoric” becomes
““hydroflouric hydroflouric acid”acid”
Naming of ternary acids
Step 1:Name the polyatomic
Step 2: Change “-ate” to “-ic”
or “-ite” to “-ous”
Step 3: Slap acid on the end
The Nomenclature of The Nomenclature of ACIDSACIDS
““sulfuric acid”sulfuric acid”
“ “sulfuric” becomessulfuric” becomes““sulfate” becomessulfate” becomes
Example #1: HExample #1: H22SOSO44
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for binary acidsRules for Writing Formulas for binary acids
Step 1: Does the name begin with
“hydro-”? If yes, then…
Step 2:Write the symbol for the
hydrogen ion followed by the
symbol for the second element
Step 3: Crisscross the charges and write them as subscripts.
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for binary acidsRules for Writing Formulas for binary acids
Example: hydrosulfuric acid
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for binary acidsRules for Writing Formulas for binary acids
Example: hydrosulfuric acid
H+1 S-2
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for binary acidsRules for Writing Formulas for binary acids
Example: hydrosulfuric acid
H+1 S-2
H+1 S-2
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for binary acidsRules for Writing Formulas for binary acids
Example: hydrosulfuric acid
H+1 S-2
H+1 S-2
H2S
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for ternary acidsRules for Writing Formulas for ternary acids
Step 1: Does the name begin with
“hydro-”? If no, then…
Step 2:Write the symbol for the
hydrogen ion followed by the
appropriate polyatomic ion
Step 3: Crisscross the charges and write them as subscripts.
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for binary acidsRules for Writing Formulas for binary acids
Example: sulfuric acid
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for binary acidsRules for Writing Formulas for binary acids
Example: sulfuric acid
H+1 SO4-2
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for binary acidsRules for Writing Formulas for binary acids
Example: sulfuric acid
H+1 SO4-2
H+1 SO4-2
The Nomenclature of The Nomenclature of ACIDSACIDS
Rules for Writing Formulas for binary acidsRules for Writing Formulas for binary acids
Example: sulfuric acid
H+1 SO4-2
H+1 SO4-2
H2SO4
The Nomenclature of The Nomenclature of ACIDSACIDS
1. HI 1. HI
2. phosphoric acid2. phosphoric acid
3. hydrobromic acid 3. hydrobromic acid
4. H4. H22SOSO33
Name the chemical or write Name the chemical or write the symbolthe symbol
The Nomenclature of The Nomenclature of ACIDSACIDS
hydroiodic acid
1. 1.
2. phosphoric acid2. phosphoric acid
3. hydrobromic acid 3. hydrobromic acid
4. H4. H22SOSO33
Name the chemical or write Name the chemical or write the symbolthe symbol
The Nomenclature of The Nomenclature of ACIDSACIDS
H3PO4
hydroiodic acid
1. 1.
2. 2.
3. hydrobromic acid 3. hydrobromic acid
4. H4. H22SOSO33
Name the chemical or write Name the chemical or write the symbolthe symbol
The Nomenclature of The Nomenclature of ACIDSACIDS
HBr
H3PO4
hydroiodic acid
1. 1.
2. 2.
3. 3.
4. H4. H22SOSO33
Name the chemical or write Name the chemical or write the symbolthe symbol
The Nomenclature of The Nomenclature of ACIDSACIDS
sulfurous acid
HBr
H3PO4
hydroiodic acid
1. 1.
2. 2.
3. 3.
4. 4.
Name the chemical or write Name the chemical or write the symbolthe symbol
The Nomenclature of The Nomenclature of ACIDSACIDS
pH Scale
We use this scale to measure the strength of an acid or base.
pH is defined as the –log[H+]
pH can use the concentration of hydronium ions or hydrogen ions.
pH Scale
Acid Base
0
7
14
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515
pH of Common Substances
Timberlake, Chemistry 7th Edition, page 335
The pH ScalepH scale ranges from 0 -14
pH 7 is neutral; neither acid nor base
Pure water is pH 7
Low pH (0-6.9) = acid
High pH (7.1-14) = base
The closer to the ends of the scale, the stronger the solution is
Acid
Any substance which has a pH of value of less than 7 is considered an acid
0--------------7---------------14
Acid Neutral Base
Base
Any substance which has pH value greater than 7 is a base
0--------------7---------------14
Acid Neutral Base
pH 7
A pH of 7 is called neutral—neither acid nor base.
0------------7------------14
Acid Neutral Base
The pH ScaleEach pH unit is Each pH unit is 1010 timestimes as large as the as large as the previous oneprevious one
A change of 2 pH units means A change of 2 pH units means 100 times100 times more more basic or acidicbasic or acidic
Each pH unit is Each pH unit is 1010 timestimes as large as the as large as the previous oneprevious one
A change of 2 pH units means A change of 2 pH units means 100 times100 times more more basic or acidicbasic or acidic
x10x10 x100x100
The pH Scale
Careful measurement is important
A mistake of one pH unit means 10 times too much or too little!
x10x10 x100x100
How Do We Measure pH?
One way to measure pH is by using special strips of paper called pH paper
How Does It Work?The paper is treated with chemicals (indicators) that change color to show the pH.When the paper touches the substance being tested, it turns a specific color to tell if the substance is an acid or a base.
To Use pH PaperPlace the edge of the pH paper into the mixture.Observe the color change of the pH paperMatch the resulting color to the colors listed on the outside of the pH paper package.The colors match with a correlated pH number.The number is the pH value of the sample.
A)The Oldest Theory is the Arrhenius Theory
Historical views on acidsHistorical views on acids
Arrhenius looked at the substances which were called acids. Some of these substances were known from even before the days of alchemy.
They taste sour, turn blue litmus to red, neutralize bases, release hydrogen gas when added to an active metal and release carbon dioxide when added to a carbonate.
Arrhenius said these properties were due to the production of H+ ions when acids dissolve in water.
He looked at the properties of bases. They taste bitter, feel slippery (soapy), turn red litmus blue and neutralize acids.
Arrhenius said these properties were due to the production of OH- ions when bases are dissolved in water.
Historical views on acidsHistorical views on acids
Ionization
+Cl HH
HO
+H
HH O Cl+
• O2 found in oxyacids (e.g. H2SO4) was originally thought to cause acidic properties. Later, H2 was implicated, but it was still not clear why CH4 was neutral.
• Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H2
+ ions in solution.
Historical views on acidsHistorical views on acids
• The more recent Bronsted-Lowry concept is that acids are H+ (proton) donors and bases are proton acceptors
+Cl HH
HO
+H
HH O Cl+
The Bronsted-Lowry conceptThe Bronsted-Lowry concept• In this idea, the ionization of an acid by water
is just one example of an acid-base reaction.
• Acids and bases are identified based on whether they donate or accept H+.
• “Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H+.
+Cl HH
HO
+H
HH O Cl+
acid base conjugate acid conjugate base
conjugate acid-base pairs
Today we know that a bare proton does not exist in water, it forms a chemical bond with a water molecule forming the H3O+. This ion is called the hydronium ion.
The Bronsted-Lowry conceptThe Bronsted-Lowry concept
H2O H3O+ + OH-
“Pure” water is always a dynamic mixture of these three substances in equilibrium
1) A B/L acid is the species which donates a proton in a proton transfer reaction. What is meant by a proton here?
2) A B/L base is the species which _________ .
3) A B/L acid is the species which _________
The Bronsted-Lowry conceptThe Bronsted-Lowry concept
4) A specific strong acid - base reaction:
HCl(aq) + H2O(l) H3O+(aq) + Cl-
(aq)
HCl(aq) is the ___________________ .
H2O(l) is the ________________ .
H3O+(aq) is the ________________________.
Cl-(aq) is the _________________________ .
CH3COOH is the _____________________.
H2O is the _________________________.
H3O+ is the ____________________.
CH3COO- is the _____________________.
Practice problemsPractice 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
1. HF(aq) + SO32–(aq)
2.CO32–(aq) + HC2H3O2(aq)
3. H3PO4(aq) + OCl –(aq)
OYO PracticeOYO Practice
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: OYO PracticeAnswers: OYO Practice1.
2.
3.
Reaction Types
Neutralization Reaction – a special double replacement reaction in which an acid is combined with a base and yields water and a salt.
HHClCl ++ NaNaOHOH NaNaClCl ++ HH22OOHHClCl ++ NaNaOHOH NaNaClCl ++ HH22OO
TitrationsIn a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete.
Equivalence point – the point at which the reaction is neutral
Indicator – substance that changes color at (or near) the equivalence point
Slowly add baseto unknown acidUNTIL the indicatorchanges color
4.7
End point – the point at which the reaction becomes complete
What volume of a 1.420 M NaOH solution isRequired to titrate 25.00 mL of a 4.50 M H2SO4 solution?
WRITE THE CHEMICAL EQUATION!
H2SO4 + 2NaOH 2H2O + Na2SO4
Ma x Va = Mb x Vb