Lab. 2 10.1 Acids and Bases Arrhenius Acid Arrhenius Acid Produce H + ions in water. Arrhenius Base...

Lab

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10.1 Acids and Bases

Arrhenius Acid Produce H+ ions in water.

Arrhenius Base Produce OH- ions in water.

Svante August Arrhenius

1884 – Acid & base defined in terms of their effect on water.

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In water, the hydrogen ion is not a bare proton, but a proton bonded to water.

The hydrogen ion (H+) in water hydronium ion

H+ and H3O+are used interchangeably

Hydrogen chloride gas completely ionizes in water = K >> 1

Acid strength is based on the amount of H3O+ in solution and a strong acid is one that completely ionizes in aq. solution.

Simple representation:HCl H+ + Cl-HCl (aq) = Hydrochloric acid = is a strong acid

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Common strong acids and bases

SAIn general:Highly electronegativeVery polar bond

SBIn general:Group I & II hydroxides

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Bronsted-Lowry Acids and BasesAcids donate a proton (H+) Bases accept a proton (H+)

Johannes Nicolaus Brønsted

1923o acid-base reactions can be seen as

proton-transfer reactions o acids and bases can be defined in

terms of this proton (H+) transfer.

Thomas Martin Lowry

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Conjugate Acid-Base Pairs

Each pair is related by a loss and gain of one H+

Conjugate acid has one more H

Conjugate base has one less H

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Naming of Acids

Binary Acids 2 elements

H + nonmetal

1st the prefix hydro

2nd name of the nonmetal is modified:

add suffix ­-ic­

3rd add the word acid.

What is the name for H2S?

Hydrosulfuric acid

What is the name for HI?

Hydroiodic acidHCl hydrochloric acid

Ternary Acids 3 elementsH + polyatomic ion

1st change the ending of the polyatomic ion:-ate to -­ic­­-ite to ­-ous­

2nd add the word acid

H2SO4 SO42- sulfate sulfuric acid

H2CO3 CO32- carbonate carbonic acid

What is the name for HNO3 ?

Nitric acid

What is the name for H3PO4 ?

Phosphoric acid

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Strong acids have Ka 1Weak acids have Ka 1

10.2 Strengths of Acids and Bases

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The stronger the acid the weaker its conjugate base

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Self-ionization of water

Water is an amphoteric substance, it can behave as an acid or a base.

10.3 Ionization of Water

2H2O (l) H3O+ (aq) + OH- (aq)

To Calculate the hydrogen ion concentration

To Calculate the hydroxide ion concentration

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To determine pH on your calculator

[H+] = 6.4 x 10-2

pH = 1.19

Significant figures using logs

10.4 The pH Scale

In order to simplify the numbers associated with acid or base strength, one takes the log as follows:

pH = - log [H+]

2. get the log 3. get the negative 1. enter 6.4 x 10-2

Answer?

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Notice how at a pH of 1 the concentration of the H+ is 1x10-1. Notice that at a pH of 14 the concentration is a much smaller value, 1x10-14. The reason that the more acidic solution has the smaller pH value is because the pH is really measuring the negative exponent. The more negative the value becomes, the smaller the concentration.

[H+] (decimal) [H+] (sci. notation)1 1x100

0.1 1x10-1

0.01 1x10-2

0.001 1x10-3

0.0001 1x10-4

0.00001 1x10-5

0.000001 1x10-6

0.0000001 1x10-7

0.00000001 1x10-8

0.000000001 1x10-9

0.0000000001 1x10-10

0.00000000001 1x10-11

0.000000000001 1x10-12

0.0000000000001 1x10-13

0.00000000000001 1x10-14

pOH = -log [OH-]pH + pOH = 14

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pH can be calculated and measured

pH meter• Tests the voltage of the electrolyte• Converts the voltage to pH• Very cheap, accurate• Must be calibrated with a buffer solution

pH calculations – Solving for [H+]pH calculations – Solving for [H+]

[H+] = 10-3.12 = 7.6 x 10-4 M

If the pH of Coke is 3.12, [H+] = ???Because pH = - log [H+]

then - pH = log [H+]

Take antilog (10x) of both sides and get10-pH = [H+]

to find antilog on your calculator, look for “Shift” or “2nd function” and then the log button

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In a logarithmic scale a pH change of one unit equals a tenfold change in the conc. of H+ ions.

Therefore gastric acid is 100 times (2x10) more acidic than orange juice, and black coffee is 10 times (1x10)more acidic than urine.

pH can be calculated, measured and estimated

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10.7 BuffersThe components of a buffer solutionAre acid-base conjugate pairs.Can be a weak acid and a salt of its conjugate base. Can also be a weak base and a salt of its conjugate acid.Purpose: to maintain the pH of a solution constant.

The phosphate buffer system: H2PO4- and HPO4

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The bicarbonate buffer: H2CO3 and HCO3-

Added acid: H2CO3 + H2O H3O+ + HCO3

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Added base: H2CO3 + OH- H2O + HCO3

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H2CO3 + H2O ↔ H3O+ + HCO3-

H2PO4- + H2O ↔ H3O+ + HPO4

2-

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When an acid or base is added to water, the pH changes drastically.

To a buffer solution, the pH does not change very much, pH is maintained.

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[H3O+] = Ka x [weak acid]

[conjugate base]

To calculate the pH of a buffer solution:

Buffers are usually a mixture of a weak acid and the salt of its conjugate base.

[H3O+] = Ka x [HA]

[A-]

pH = - log [H3O+]