Some of our favorite foods make our tongue curl up because they are SOUR. Acids and Bases.

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.

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

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

Example #1: HFExample #1: HF

““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

““sulfuric acid”sulfuric acid”

“ “sulfuric” becomessulfuric” becomes““sulfate” becomessulfate” becomes

Example #1: HExample #1: H22SOSO44

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.

Example: hydrosulfuric acid

H+1 S-2

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.

Example: sulfuric acid

H+1 SO4-2

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

hydroiodic acid

2. phosphoric acid2. phosphoric acid

4. H4. H22SOSO33

hydroiodic acid

4. H4. H22SOSO33

hydroiodic acid

4. H4. H22SOSO33

sulfurous acid

hydroiodic acid

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

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

Any substance which has a pH of value of less than 7 is considered an acid

0--------------7---------------14

Acid Neutral Base

Any substance which has pH value greater than 7 is a base

0--------------7---------------14

Acid Neutral Base

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.

Ionization

+Cl HH

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.

• The more recent Bronsted-Lowry concept is that acids are H+ (proton) donors and bases are proton acceptors

+Cl HH

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

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-

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)

acidbase conjugate acidconjugate baseOH

–(aq) + HCO3–(aq) CO3

2–(aq) + H2O(l)

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)

acidbase conjugate acidconjugate baseCO3

2–(aq) + HC2H3O2(aq) C2H3O2–(aq) + HCO3

–(aq)

acid base conjugate acidconjugate baseH3PO4(aq) + OCl

–(aq) H2PO4–(aq) + HOCl(aq)

Answers: OYO PracticeAnswers: OYO Practice1.

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

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

Some of our favorite foods make our tongue curl up because they are SOUR. Acids and Bases.

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