AcidsA Swedish chemist, named Arrhenius in 1890 proposed that an acid bedefined as any substance that, when added to water, increases the hydroniumion concentration. Hydronium is defined as H3O+.

Water will attract a H+ ion to produce a hydronium ion.

H2O + H+ H3O+

Many times we will only write the H+ to represent the hydronium ion.

For example if HCl(s) is added to water the following will occur.

HCl(g) H+(aq) + Cl-(aq)

H2O(l) + H+(aq) H3O+(aq)Adding the two reactions together

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

Strong Acids vs. Weak Acids

Strong acids will tend to go to completion when dissolved in water, weakacids do not.

HOCl(l) + H2O(l) H3O+(aq) + ClO−(aq)

HNO3(l) + H2O(l) H3O+(aq) + NO3−(aq)

Weak Acid

Strong Acid

Bases

Arrhenius defined bases as any substance when dissolved in water will produce hydroxide ions. (OH-)

KOH(s) K+(aq) + OH-(aq)

If they go to completion when dissolved in water they are said to be strongbases, if they do not dissolve well and produce few hydroxide ions they arecalled weak bases.

Another term used to describe basic solutions is alkaline. An alkaline solutionis very basic. This term comes from group 1 of the periodic table which always makes strong basic solution.

The definitions of Arrhenius acid and Arrhenius base given earlier in thisbook are variants of the definitions of acid and base originally proposedby Arrhenius in the late 19th century. One drawback that the Arrheniusdefinitions have is that they are limited to aqueous solutions: HCl, forinstance, should be considered an acid whether it is in the form of a puregas or in aqueous solution. Another limitation is that the Arrhenius definitioncannot classify substances that sometimes act as acids and sometimesact as bases.

In 1923, the Danish chemist Johannes Brønsted proposed a broader definitionof acid. Surprisingly, the same year, the British scientist Thomas Lowry happened to make exactly the same proposal independently. Theiridea was to apply the name acid to any species that can donate a proton.Recall that a proton is a hydrogen atom that has lost its electron; it is ahydrogen ion and can be represented as H+. Such molecules or ions are now called Brønsted-Lowry Acids. Proton acceptors are called Brønsted-Lowry Bases.

Brønsted-Lowry Acids

H2S + H2O → H3O+ + HS−

Lost a proton, H+, thereforeis the acid.

Gained a proton, H+, thereforeis the base.

Properties of Acids and Bases

Acids Bases

Are excellent electrolytes Are excellent electrolytes

Have a pH below 7 Have a pH above 7

Will react with many metals to produce hydrogen gas

Are said to be acidic

Are said to be basic or alkaline

Acids will react with metal to produce hydrogen gas

The proton, H+, will react with many metals to producehydrogen gas using a single displacement reaction.

Any metal located above the H2 on table J will reactwith an acid to produce hydrogen gas.

Write out the chemical react that will occur between the listed acid and metal

Mg + HCl

Na + HCl

Cu + HCl

Zn + HCl

Neutralization

Neutralization reaction the reaction of the ions that characterize acids (hydronium ions) and the ions that characterize bases (hydroxide ions) to form water molecules and a salt (ionic compound).

HCl(aq) + KOH(aq) Acid Base

H+(aq) + Cl-(aq) + K+(aq) + OH-(aq)

H2O(l) + KCl(aq)Water Salt

pH

A value used to express the acidity or alkalinity of a solution; a pH of 7 is neutral, a pH of less than 7 is acidic, and a pH of greater than 7 is basic

pH < 7 pH = 7 pH > 7

Water is neutral because it is made up of one acid (H+), and one base (OH-).

pH factors of 10

Each pH number indicated a change of concentration of hydronium ionconcentration by a factor of 10.

For example:If a sample of pool water has a pH of 8 and after adding chlorine for cleaningthe pH changes to 5 how much has the hydronium ion concentration changed?

pH

8 7 6 5

10 10 10 x x

10 x 10 x10 = 1000

The hydronium ion concentration changes by a factor of 1000

Because pH is dropping into the acid range, this indicated an increase in hydronium ion concentration.

Indicators

Certain dyes, known as indicators turn different colors in solutions ofdifferent pH.

Dozens of indicator dyes are available. Some indicators, such as litmus,are natural products, but most are synthetic. Each indicator has itsown colors and its individual range of pH over which it changes shade. Bysuitably blending several indicators, chemists have prepared “universalindicators,” which turn different colors throughout the entire pH range.

Titrations

The gradual addition of one solution to another to reach an equivalence point is called a titration. The purpose of a titration is to determine the concentration of an acid or a base. In addition to the two solutions, the equipment needed to carry out a titration usually includes two burets, a titration flask, and a suitable indicator.

The formula used for titrations is from your reference tables.

A solution of a base differs from a solution of an acid in that the solution of a base1. is able to conduct electricity 2. is able to cause an indicator color change 3. has a greater [H3O+] 4. has a greater [OH-]

Which pH value indicates the most basic solution?1. 7 2. 8 3. 3 4. 11

A 3.0-milliliter sample of HNO3 solution is exactly neutralized by 6.0 milliliters of 0.50 M KOH. What is the molarity of the HNO3 sample? 1. 1.0 M 2. 0.50 M 3. 3.0 M 4. 1.5 M

Which solution will turn litmus from red to blue?1. H2S(aq) 2. NH3(aq) 3. SO2(aq) 4. CO2(aq)

Which substance is always produced in the reaction between hydrochloric acid and sodium hydroxide?1. water 2. hydrogen gas 3. oxygen gas 4. a precipitate

Equal volumes of 0.1 M NaOH and 0.1 M HCl are thoroughly mixed. The resulting solution has a pH closest to 1. 5  2. 7  3. 3  4. 9

As an aqueous solution becomes more acidic, the hydroxide ion concentration1. decreases 2. increases 3. remains the same

What produces hydrogen ions as the only positive ions in aqueous solution?1. KOH 2. HBr 3. NH3 4. NaCl

When the pH of a solution changes from a pH of 5 to a pH of 3, the hydronium ion concentration is1. 0.01 of the original content 2. 0.1 of the original content 3. 10 times the original content 4. 100 times the original content