15,16-1

CHAPTER 15 & 16

(Acids & Bases)

Acids are substances which generally have a hydrogen in the front of their formula

Bases (alkaline) are substances which generally have a hydrogen in the back of their formula

Salts are ionic compounds of metal-nonmetal composition.

A binary acid is an acid that contains only two different elements: hydrogen and one of the more electronegative elements.

Ex: HCl - hydrochloric acid

An oxyacid is an acid that is a compound of hydrogen, oxygen, and a third element, usually a nonmetal.

Ex: HNO3 - nitric acid

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Some Properties of acids:

  1. Aqueous solutions of acids have a sour taste.

[never use the "taste test" to find out]

Ex: lemons, oranges

2. Acids change the color of acid-base indicators.

*Ex: Turns blue litmus red

Phenolphthalein is colorless in acids

Bromothymol blue is yellow in acids

3. Some acids react with active metals to release hydrogen gas.

Ex: Zn (s) + H2SO4 (aq) --> ZnSO4 (aq) + H2 (g)

4. Acids react with bases to produce salts and water.

Ex: HCl + NaOH --> NaCl + H2O

acid base salt water

6. Some acids conduct electric current

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Some Properties of bases (alkaline):

1. Aqueous solutions of bases taste bitter.

[never use the "taste test" to find out]

Ex: soap suds or limewater

  1. Bases change the color of acid-base indicators.

Ex: turns red litmus blue

phenolphthalein turns red

bromothymol blue is blue in a base

  1. Dilute aqueuos solution of bases feel slippery.

Ex: soap

  1. Bases react with acids to produce salt and water.

Ex: HCl + NaOH --> NaCl + H2O

acid base salt water

5. Bases conduct electric current.
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Industrial acids

Sulfuric acid is manufactured in the United States more than any other chemical. Approximately 35 million tons each year.

Uses: -to make phosphoric acid

-production of cellulose products

-refining petroleum.

Nitric acid and phosphoric acid are and essential part of fertilizer production

Hydrochloric acid is the most expensive and most widely used as a lab reagent

Nearly all fruits contain acids15,16-5

  • Lemons, oranges, and grape fruits contain citric acid.
  • Apples contain malic acid
  • The souring of milk produces lactic acid
  • Vinegar is acetic acid
  • The secretion in the human stomach is about 0.4% hydrochloric acid

Several substances long known as bases are commonly found in homes.

  • Ammonia and ammonia solutions are familiar cleaning agents
  • Lye is a commercial grade of sodium hydroxide-used for cleaning clogged sink drains
  • Milk of magnesia is a suspension of magnesium hydroxide in water
  • Soap is a base
  • Tums and Rolaids are both bases

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According to Arrhenius

Acids are chemical compounds that increase the concentration of hydrogen ions in aqueous solution.

Ex: HCl when dissolved in water H+aq +Cl-aq

Bases are substances that increase the concentration of hydroxide ions in aqueous solution.

Ex: NaOH (aq) --> Na+ (aq) + OH- (aq)

Ca(OH)2 (aq) --> Ca++ (aq) + OH- (aq)

According to Bronsted-Lowry

An acids is a molecule or ion that is a proton donor.

Ex: NH3 + H2O <--> NH4+ + OH-

in the above reaction water is considered an acid

A Bases is a molecule or ion that is a proton acceptor

Ex: HCl + H2O --> H3O+ + Cl-

in the above reaction water is considered a base

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According to Lewis:

An acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond.

A base is an atom, ion, or molecule that donates an electron pair to form a covalent bond.

A conjugate base is the species that remains after an acid has given up a proton

A conjugate acid is the species formed when a base gains on a proton

Example:

HSO4- + H2O --> H3O+ + SO4--

| | | |

acid base conjugate acid conjugate base

H3O+ + SO4-- --> HSO4- + H2O

| | | |

acid base conjugate acid conjugate base

  • In the above example, HSO4- and SO4-- are a conjugate acid-base pair
  • In the above example, H3O+ and H2O are a conjugate acid-base pair

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Fill in the appropriate acid or conjugate base

AcidConjugate Base

HCl______

HNO3______

NH4+______

H2SO4______

______SO4--

______F-

______C2H3O2-

______NH3

Any species than can react as either an acid or a base is described as amphoteric.

Ex: HCl + H2O --> H3O+ + Cl-[water is a base]

NH3 + H2O --> NH4+ + OH-[water is an acid]

Neutralization is the reaction of hydronium ions and hydroxide ions to form water molecules.

Ex: HCl + NaOH --> NaCl + H2O

acid base salt water

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A salt is an ionic compound composed of a cation from a base and an anion from an acid.

Ex: HCl + NaOH --> NaCl + H2O

acid base salt water


In the self-ionization of water, two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton.

Hydronium Hydroxide

ion ion

For water at 25 degree C:

[H3O+] = 10-7 mole/L[OH-] = 10-7 mole/L

or [H3O+] = [OH-] = 10-7 mole/L

If the H3O+ ion concentration in a solution exceeds 10-7 mole/L, then the solution is acidic

Ex: A soln containing 10-5 mole H3O+ ion

per liter of soln is acidic

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If the OH- ion concentration exceeds 10-7 mole/L, then the solution is basic

Ex: A soln containing 10-4 mole OH- ion per liter of soln is basic

The product of [H3O+] and [OH-] remains constant in water:

[H3O+] x [OH-] = constant

10-7 mole/L x 10-7 mole/L = 10-14 mole2/L2

[H3O+] x [OH-] = 10-14 mole2/L2

This means that if the concentration of one is known then the other can be calculated

Ex: A solution of NaOH has a concentration of 0.01-M. Calculate the concentration of [H3O+].

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The pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration or more simply:

pH = - log [H3O+]

The pOH of a solution is defined as the negative of the common logarithm of the hydroxide ion concentration or more simply:

pH = - log [OH-]

Ex: Pure water is slightly ionized, and at 25oC contains 0.0000001 moles of H3O+ per liter. Calculate the pH of water.

Ex: Determine the pH of a 0.001-M HCl solution.

Ex: What is the pH of a 0.001-M NaOH solution

Solutions with a pH < 7 are acidic

Solutions with a pH > 7 are basic

Solutions with a pH = 7 are neutral

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A titration is the controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration.

An equivalence point is the point at which the two solution used in a titration are present in chemically equivalent amounts.

An end point is the point in a titration at which an indicator changes color.

A standard solution contains the precisely known concentration of a solute.

A primary standard is a highly purified solid compound used to check the concentration of the know solution in a titration.