2. Topic 18 Acids and Bases: Basic Concepts Properties of Acids and Bases
Although taste is not a safe way to classify acids and bases, you probably are familiar with the sour taste of acids.
Lemon juice and vinegar, for example, are both aqueous solutions of acids.
Bases, on the other hand, taste bitter.

3. Topic 18 Acids and Bases: Basic Concepts Properties of Acids and Bases
Bases have a slippery feel. Like taste, feel is not a safe chemical test for bases, but you are familiar with the feel of soap, a base, on the skin.

4. Topic 18 Acids and Bases: Basic Concepts
Reactions with Metals and Carbonates
Another characteristic property of an acid is
that it reacts with metals that are more active than hydrogen.
This property explains why acids corrode most metals.

5. Topic 18 Acids and Bases: Basic Concepts
Submicroscopic Behavior of Acids
The submicroscopic behavior of acids when they dissolve in water can be described in several ways.
The simplest definition is that an acid is a substance that produces hydronium ions when it dissolves in water.
A hydronium ion, H3O+, consists of a hydrogen ion attached to a water molecule.

6. Topic 18 Acids and Bases: Basic Concepts
Submicroscopic Behavior of Acids
When HCl dissolves in water, it produces hydronium ions by the reaction shown below.
HCl is definitely an acid; it produces H3O+ when dissolved in water.

7. Topic 18 Acids and Bases: Basic Concepts Monoprotic Acids
Acids such as acetic acid, HC2H3O2, and hydrochloric acid, HCl, are called monoprotic acids.
Monoprotic acids contain only one acidic hydrogen.

8. Topic 18 Acids and Bases: Basic Concepts Diprotic and Triprotic Acids
All acids that have more than one acidic hydrogen per molecule are called polyprotic acids.
Polyprotic acids with two acidic hydrogens are diprotic acids.

9. Topic 18 Acids and Bases: Basic Concepts
Submicroscopic Behavior of Bases
The behavior of bases is also described at the molecular level by the interaction of the base with water.
A base is a substance that produces hydroxide ions, OH –, when it dissolves in water.
There are two mechanisms by which bases produce hydroxide ions when they dissolve in water.

10. Topic 18 Acids and Bases: Basic Concepts
Simple Bases: Metal Hydroxides
The simplest kind of base is a water-soluble ionic compound, such as sodium hydroxide, that contains the hydroxide ion as the negative ion.
When NaOH dissolves in water, for example, it dissociates into aqueous sodium ions and hydroxide ions, as shown below.

11. Topic 18 Acids and Bases: Basic Concepts Strong Acids
HCl is a strong acid because no HCl molecules are in a water solution of HCl.
Because of the strong attraction between the water molecules and HCl molecules, every HCl molecule ionizes.

12. Topic 18 Acids and Bases: Basic Concepts Strong Bases
Sodium hydroxide, NaOH, is a strong base because when NaOH dissolves in water, all NaOH formula units dissociate into separate sodium and hydroxide ions.
The dissociation of the base is complete.

13. Topic 18 Acids and Bases: Basic Concepts Weak Acids
Acetic acid, HC2H3O2, is a good example of a weak acid. The molecular structure of a weak acid determines the extent to which the acid ionizes in water. A solution of weak acid contains a mixture of
un-ionized acid molecules, hydronium ions, and the corresponding negative ions.

14. Topic 18 Acids and Bases: Basic Concepts Weak Acids
The concentration of the un-ionized acid is always the greatest of the three concentrations.

15. Topic 18 Acids and Bases: Basic Concepts Weak Bases
Ammonia is a weak base because most of its molecules don’t react with water to form ions.
Other examples of bases that produce so few OH– ions that they are considered to be weak bases are Al(OH)3, and Fe(OH)3.

16. Topic 18 Acids and Bases: Basic Concepts Interpreting the pH Scale
pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic.
As the pH drops from 7, the solution becomes more acidic.
As pH increases from 7, the solution becomes more basic.

17. Topic 18 Acids and Bases: Basic Concepts Measuring pH
pH is convenient because there are simple methods for measuring it in the lab or in the field.
Indicators register different colors at different pHs.
pH meters are instruments that measure the exact pH of a solution.

18. Topic 18 Acids and Bases: Basic Concepts The pH Scale
pH is a mathematical scale in which the concentration of hydronium ions in a solution is expressed as a number from 0 to 14.
A scale of 0 to 14 is much easier to work with than a range from 1 to 10–14 (100 to 10–14).
The pH scale is a convenient way to describe the concentration of hydronium ions in acidic solutions, as well as the hydroxide ions in basic solutions.

19. In the more inclusive Brønsted-Lowry model, an acid is a hydrogen-ion donor and a base is a hydrogen-ion acceptor.

20. Topic 18 Acids and Bases: Additional Concepts Buffers Defined
A buffer is a solution that resists changes in pH when moderate amounts of acids or bases are added.
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21. Topic 18 Acids and Bases: Additional Concepts Buffers Defined
It contains ions or molecules that react with OH– or H+ if one of these ions is introduced into the solution.
Buffer solutions are prepared by using a weak acid with one of its salts or a weak base with one of its salts

22. Topic 18 Acids and Bases: Additional Concepts Buffers Defined
These pH changes are insignificant when you compare them to the changes that occur in the unbuffered solution.
These two buffer systems are common ones used in many laboratories.
Blood has many buffer systems to maintain its constant pH of 7.4.

23. Topic 18 Acids and Bases: Additional Concepts pH and pOH
Because the concentrations of H+ ions are often very small numbers, the pH scale was developed as a more convenient way to express H+ ion concentrations.
The pH of a solution equals the negative logarithm of the hydrogen ion concentration.

24. Topic 18 Acids and Bases: Additional Concepts pH and pOH
The pH scale has values from 0 to 14.
Acidic solutions have pH values between 0 and 7, with a value of 0 being the most acidic.
The pH of a basic solution is between 7 and 14 with 14 representing the most basic solution.
A neutral solution has a pH of 7.

25. Topic 18 Acids and Bases: Additional Concepts pH and pOH
Chemists have also defined a pOH scale to express the basicity of a solution.
The pOH of a solution is the negative logarithm of the hydroxide ion concentration.

26. Topic 18 Acids and Bases: Additional Concepts pH and pOH
If either pH or pOH is known, the other may be determined by using the following relationship.
The pH and pOH values for a solution may be determined if either [H+] or [OH–] is known.
The following example problem shows you how to calculate pH and pOH.

27. Topic 18 Acids and Bases: Additional Concepts
Calculating pH and pOH from [H+]
To find pOH, recall that pH + pOH =
Isolate pOH by subtracting pH from both sides of the equation.

28. Topic 18 Acids and Bases: Additional Concepts
Calculating pH and pOH from [H+]
Substitute the value of pH and solve.
The pOH of the solution is
As you might expect, the carbonated soft drink is acidic.