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Acids, Bases and Salts Acids, Bases and Salts

Version 1.0

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Acid Properties• sour taste• change the color of litmus from blue to

red.• react with

– metals such as zinc and magnesium to produce hydrogen gas

– hydroxide bases to produce water and an ionic compound (salt)

– carbonates to produce carbon dioxide.

These properties are due to the release of hydrogen ions, H+, in water solution.

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Base Properties

• bitter or caustic taste

• a slippery, soapy feeling.

• the ability to change litmus red to blue

• the ability to interact with acids

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Uses of acids and basesMany of the things we eat & use today are made up of acids and bases.

Examples:

Sulfuric acid-car batteries,acid rain

Hydrochloric acid-stomach acid

Sodium hydrogen carbonate-baking soda and cooking

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Uses of Acids/ Bases Contd., DNA,the building block of life, stores genetic information.

Amino acids, the building blocks of proteins.

Found in movies: Acids in Jurassic Park (DNA) and in Aliens (acidic blood).

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Arrhenius Acid/Base Definition

• Svante Arrhenius was a Swedish scientist who lived from 1859-1927.

• In 1884 he advanced a theory of acids and bases.

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An Arrhenius acid “is a hydrogen-containing substance that dissociates to produce hydrogen ions.”

HA → H+ + A-

Acid

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An Arrhenius base is a hydroxide-containing substance that dissociates to produce hydroxide ions in aqueous solution.

MOH → M+(aq) + OH-(aq)Base

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An Arrhenius acid solution contains an excess of H+ ions because an Arrhenius acid increases H+ concentration,

when dissolved in water.

An Arrhenius base solution contains an excess of OH- ions because it increases OH- concentration, when dissolved in

water.

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Bronsted and Lowry Definition

• J.N. Bronsted (1897-1947) was a Danish chemist and T. M. Lowry (1847-1936) was an English chemist.

• In 1923 they advanced their theory of acids and bases.

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A Bronsted-Lowry acid is a proton (H+) donor.

A Bronsted-Lowry base is a proton (H+) acceptor.

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HCl (aq) + H2O(l) → H3O+(aq) + Cl-(aq)

proton acceptorBronsted-Lowry Baseproton donorBronsted-Lowry Acid

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Conjugate acid-base pairs differ by a single proton.

1. Are sulphate and sulfuric acid conjugate acid and base of each other? Why or why not?

2. Write conjugate base of H3PO4.

3. Write conjugate acid of NO3-

1. No, they differ by 2 protons. 2. H3PO4. 3. HNO3

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. A strong acid has a weak conjugate base and vice versa.

List of strong Acids: HCl, HNO3, H2SO4, HI, HBr, HClO3, HClO4

List of Strong Bases: All group 1 and 2 metal hydroxides

Monoprotic Acids: Have one proton that can be donated. Ex. HCl, HNO3, H C2H3O2

Diprotic Acids: Have two protons that can be donated. H2SO4

Polyprotic Acids: Have more than two protons that can be donated. Ex. H3PO4

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Compare the strengths of two acids in the following reactions. What does the strength of acid have to do with the direction in which this reaction occurs? (Forward reaction is

favored, why?)

Base 1

Acid 1

HCl(g) + → Cl-(aq) + H3O+(aq)H2O (l)

Acid

2

Base

2

If strong acid will completely ionize

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Lewis Acids and Bases

• In 1923 G. N. Lewis developed a more comprehensive theory of acids and bases.

• The Lewis theory deals with the way in which a substance with an unshared pair of electrons reacts in an acid-base type of reaction.

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A Lewis acid is an electron-pair acceptor.

A Lewis base is an electron-pair donor.

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Lewis AcidElectron Pair Acceptor

Lewis BaseElectron Pair Donor

Electron pair donated to H+

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In aqueous solution, the H+ or H3O+ ions are responsible for the characteristic reactions of acids.

Reactions of AcidsReactions of Acids

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HBr(aq) + KOH(aq) → KBr(aq) + H2O(l)

Reaction with Bases The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water:

2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l)

acid base salt

acid base salt

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HBr(aq) + KOH(aq) → KBr(aq) + H2O(l)

The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water:

2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l)

acid base salt

acid base salt

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Salts can be considered compounds derived from acids and bases. They consist of positive metal or ammonium ions combined with nonmetal ions (OH- and O2- excluded).

Chemists use the terms ionic compound and salt interchangeably.Salts are usually crystalline and have high melting and boiling points.

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NaOH HCl

NaCl

base acid

salt

The positive ion of the salt is derived from the base.

The negative ion of the salt is derived from the acid.

Salt Formation

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Ionization of WaterIonization of Water

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Water ionizes slightly.

base acid acid baseH2O + H2O → H3O+ + OH- →→

hydronium ion

hydroxide ion

Water ionization equilibrium can be expressed more simply as:

Kw= [H3O+] [OH-] = 1.0 x 10-14 mol/L (This expression can be used to calculate H+ or OH-)

[H3O+] or [H+]= [OH-] = 1.0 x 10-7 mol/L

What is [OH-], if [H+] is 3.0 x 10-3? ( ans: 3.3 X 10 –12 )

Two out of every 1 billion water molecules are ionized.

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Introduction to pHIntroduction to pH

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The pH ScaleThe pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration.

pH= -log [H3O+]

The pOH of a solution is defined as the negative of the common logarithm of the hydroxide ion concentration.

pOH= -log[OH-]

[H3O+] 1.0Increasing acidity

1.0x10-7

Increasing basicity1.0x10-14

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Calculation of pHCalculation of pH

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H+ OH-

pH pOH

[H+] = 1.0 X 10 ^-14/ [OH-]

[OH-] = 1.0 X 10 ^-14/ [H+]

pOH

= -log [O

H-]

[OH

-]= 10^

-pO

H

pH=

-log [H+

]

[H+

]= 10^

-pH

pH= 14- pOH

pOH= 14- pH

pH BOX

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pH = -log[H+]

[H+] = 1 x 10-5

when this number is exactly 1

pH = this number without the minus sign.

pH = 5

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pH = -log[H+]

[H+] = 2 x 10-5

when this number is between 1 and 10

The number of decimal places of a logarithm is equal to the number of significant figures in the original number.

pH is between this number and next lower number (4 and 5).one decimal place

one significant figure

ph = 4.7

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What is the pH of a solution with an [H+] of 1.0 x 10-11?

pH = - log(1.0 x 10-11)

pH = 11.00

2 decimal places

2 significant figures

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What is the pH of 0.002 M H2SO4?

[H+] = 2 x 10-3

pH = - log(2 x 10-3)

pH = 2.7

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1. What is the pH of 0.003 M NaOH?

2. What is [H+], if pH is 3.4?

[OH-] = 3 x 10-3

pOH = - log(3 x 10-3)

pOH = 2.2 14.0-2.2 = 11.8

10 -3.4 = 4 X 10 -4

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The pH scale of Acidity and Basicity

15.4

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NeutralizationNeutralization

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Neutralization: The reaction of an acid and a base to form a salt and water.

HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) acid base salt

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TitrationsTitrations

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titration: The process of measuring the volume of one reagent required to react with a measured mass or volume of another reagent.

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42.00 mL of 0.150 M NaOH solution is required to neutralize 50.00 mL of hydrochloric acid solution. What is the molarity of the acid solution?

The equation for the reaction is

molMolarity =

L

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) acid base salt

Convert mL of NaOH to liters of NaOH

The unit of volume when using molarity is liters.

Calculate the moles of NaOH that react.

0.150 mol NaOH0.004200 L = 0.00630 mol NaOH

1L

1 L42.00 mL = 0.04200 L

1000 mL

Calculate the liters of NaOH that react.

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42.00 mL of 0.150 M NaOH solution is required to neutralize 50.00 mL of hydrochloric acid solution. What is the molarity of the acid solution?

The equation for the reaction is

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) acid base salt

The mole ratio of HCl to NaOH is 1:1The moles of NaOH that react equals the moles of HCl that react.

0.00630 mol NaOH react. 0.00630 mol HCl react.

molM = =

L0.0630 mol HCl

0.05000 L

0.126 M HCl

The molarity of the HCl solution is

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Writing Net Ionic EquationsWriting Net Ionic Equations

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(H+ + Cl-) + (K+ + OH-) → K+ + Cl- + H2O

In the total ionic equation all ions present in solution are written.

H+(aq) + OH-(aq) → H2O(l)

In the net ionic equation only the ions that react are written.

HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) acid base salt

In the un-ionized equation all compounds are written using their molecular or formula expressions.

K+ ion does not react.Cl- ion does not react.Ions that do not participate in a chemical reaction are called spectator ions.