Chapter 9 Flashcards Chem

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ARRHENIUS ACID

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• An Arrhenius acid is any substance that provides hydrogenions, H+, when dissolved in water.

• HNO3is an acid: HNO3(aq) ------> H+(aq) + NO3-(aq)

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ARRHENIUS BASE

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An Arrhenius base is any substance that provideshydroxide ions, OH-, when dissolved in water.

KOH is a base: KOH(aq) -----> K+(aq) + OH-(aq)

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BRØNSTED ACID

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A Brønsted acid is any hydrogen-containing substance thatis capable of donating a proton (H+) to another substance.

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BRØNSTED BASE

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A Brønsted base is any substance capable of accepting aproton from another substance

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are Brønsted bases equilibrium?

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ye

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CONJUGATE ACIDS AND BASES

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The base formed (NO2-) when a substance (HNO2) acts as aBrønsted acid is called the conjugate base of the acid.Similarly, the acid formed (H3O+) when a substance (H2O)acts as a Brønsted base is called the conjugate acid of thebase.

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CONJUGATE ACID-BASE PAIRS

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A Brønsted acid (such as HNO2) and its conjugate base(NO2-) form what is called a conjugate acid-base pair.• The same name is given to a Brønsted base (such as H2O)and its conjugate acid (H3O+)

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Hydrochloric acid

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: HCl

Strong acid

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Nitric Acid

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Nitric Acid

Strong acid

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Sulfuric acid

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H2SO4

Strong acid

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Acetic acid

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CH3COOH

weak acid

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Carbonic acid

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H2CO3

weak acid

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•Phosphoric acid

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H3PO4

weak acid

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THE ION PRODUCT OF WATER

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1.0 * 10 ^ -14

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THE pH CONCEPT

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It is often the practice to express the concentration of H3O+inan abbreviated form called the pH rather than to usescientific notation.

t is also a common practice to represent the H3O+ion by thesimpler H+ion.

• The pH notation is defined below, using H+in place of H3O+:pH = -log[H+], or in alternate form [H+]= 1x10-pH

• Thus, the pH is seen to be the negative of the exponent usedto express the molar concentration of H+ using scientificnotation.

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Example 2: Calculate the [OH-] for a solution with a pH = 4.0

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1.0 * 10 ^ -10

1.0 * 10 ^ -14 = (1.0 * 10 ^ -4) * [OH-]

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Example 3: Calculate the pH of a solution in which[H+]= 3.6x10-4 M.

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Solution: Use the pH equation, pH = -log [H+], to findpH= -log [3.6 x 10-4], then evaluate with a calculator.

-3.4437

flip sign

3.4437 is da ph

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Example 4: Calculate the [H+] of a solution in whichpH = 5.92.

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Solution: Use the alternate pH equation, [H+] = 1 x 10-pH, tofind [H+] = 1.0 x 10 ^ -5.92, then evaluate with a calculator.

The [H+] of the solution is 1.2 x 10-6 M.

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PROPERTIES OF ACIDS

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producing H3O+ions when dissolved in water.

In addition, all acids undergo characteristic doublereplacementreactions with solid oxides, hydroxides,carbonates, and bicarbonates. These reactions are givenbelow, using hydrochloric acid, HCl(aq), as a representativeacid.

Reaction with metal oxide:

2HCl(aq) + MgO(s) → MgCl2(aq) + H2O(l)

Reaction with metal hydroxide:

2HCl(aq) + Mg(OH)2(s) → MgCl2(aq) + 2H2O(l)

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PROPERTIES OF BASES

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Their most characteristic chemical property is their ability toreact readily with acids in what is called a neutralizationreaction.

Basic solutions feel soapy or slippery to the touch andcontain the OH ion

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NEUTRALIZATION REACTIONS

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• In neutralization reactions, an acid reacts with a base toproduce a salt and water. The following are typicalneutralization reactions involving the base sodium hydroxide,NaOH, which is also known commercially as lye.

Reaction with hydrochloric acid:NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Reaction with nitric acid:NaOH(aq) + HNO3(aq) → NaNO3(aq) + H2O(l)

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THE STRENGTH OF ACIDS & BASES

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The strengthof an acid orbase isdeterminedby the extentto whichdissolved acidor basedissociates toform ions

A strong acid or base dissociates 100%, while a weak ormoderately weak one dissociates less than 100%.

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ACID DISSOCIATION CONSTANTS

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for the dissociation of a weak acid. It is represented by thesymbol Ka.• The dissociation of a weak acid in solution is represented bythe following equation in which HB represents the weak acid,and Bisthe conjugate base of the acid.

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Monoprotic acids

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give up only oneproton permolecule whendissolved in water

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Diprotic acids

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give up amaximum of twoprotons permolecule whendissolved in water

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• Triprotic acids

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give up amaximum of threeprotons permolecule whendissolved in water.

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COMMON BASES weak base

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Ammonia (NH3) is the weak base most often encountered inaddition to the anions of strong acids.

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COMMON BASES strong

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are the hydroxides ofgroup I A (1) metals (NaOH, KOH, etc.) and the hydroxides ofgroup II A (2) metals (Mg(OH)2, Ca(OH)2, etc.)

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BUFFERS

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Buffers are solutions with the ability to resist changing pH whenacids (H+) or bases (OH-) are added to them.