Acids and Bases

Property of some aqueous solutions is their ability to act

as an acid or base

Acids and Bases

Acids and bases play an important part in our lives.

Proper acidity of our blood and other body fluids is vital to our health

Many products we use are acidic• Citrus fruits contain citric acid• Aspirin is an acid• Our car batteries are filled with sulfuric

acid

Acids and Bases

Acids and bases play an important part in our lives.• Baking soda and milk of magnesia are

basic.• Antacids are basic compounds like

carbonates, bicarbonates and hydroxides

• Dilute solutions of ammonia are used for cleaning.

• Caustic sodium hydroxide can be used to clean drains.

A property of certain kinds of aqueous solutions is their

ability to act as an

ACID or a BASE

How do we know whether something is an Acid or a

Base??

Originally a chemical or solution was classified as an acid if it

had the following 3 properties:

1. It has a sour taste

2. It turns a plant dye called litmus red

3. It eats away at more active metals like zinc to produce a hydrogen gas.

Properties 2 & 3 are the most commonly used.

Properties of Bases

1.Bases also have a bitter taste. The bitter taste of milk of magnesia

2.They turn the plant dye called litmus blue.

3.Bases are also recognized because they feel slippery or soapy.

Acids

• Chemically acids have the ability to produce a hydrogen ion when dissolved in water.

• Acids may be classified as strong or weak.• Depends how easily it is for the hydrogen to

be removedStrong acids – sulfuric, nitric, HClWeak acids – citric, lactic, aceticAcids are also recognized because of their sour

taste. The tart taste of citrus fruits and vinegar are due to acids.

Bases

• Bases have the ability to pick up the hydrogen ion that is produced by the acid

• Some bases are stronger than others

• The strength of a base is determined by their ability to pick up a hydrogen ion.

A scale was developed to relate the acidity or basicity of a soltuion

• The scale related the available hydrogen ions in a solution to a numerical value.

• It is based on on 0 14• It’s called the pH scale

• The closer the pH value is to 0, the stronger the acid.• The closer the pH value is to 14, the stronger the base.• If the pH value is in the middle, or 7, the pH is neutral

Solutions may be:

strongly acidic (0 - 2),

weakly acidic (2 - 7),

neutral (pH=7),

weakly basic (7 - 12),

strongly basic (12 - 14).

More about “litmus”

Litmus paper can be used to indicate if a solution is acidic or basic.

However, it does not indicate “how acidic” or “how basic”.

What is litmus?

• Litmus is one of a large number of organic compounds (it is actually extracted from certain mosses) that change colors when a solution changes acidity at a particular point.

• Litmus is the oldest known pH indicator. • It is red in acid and blue in base. • Litmus is often impregnated onto paper to make 'litmus paper.'

Properties of Acids

An acid can be identified in the laboratory because it turns a plant pigment called litmus red.

A base can be identified in the laboratory because it turns a plant pigment called litmus blue.

Measuring pH

pH indicators can also be impregnated onto paper and used to determine pH.

Paper, called pHydrion paper, is impregnated with a universal indicator. It can be used to determine the approximate pH over a full range.

Kinds of pH paper

Kinds of pH meters

pH & Buffers• A buffer keeps something where it should

be. • It buffers adverse swings. It shields,

cushions and protects.

• Is necessary to control any change in pH in some systems• Especially in biological systems which

need to control pH• Living systems have buffering

systems in place

In order to maintain pH at a constant requires buffering of the system in a pond

Buffers

• Buffers tie up foreign acid and base

• There is a limit as to how much acid or base a buffer can absorb

• This is called buffer capacity

•A buffer would be used to maintain the pH of a product within a narrow range. •Buffers reduce the variation in the pH of a product, as shown on the graph

Examples of Buffers

• Carbonate buffer system to maintain blood pH

• Phosphate system regulate cellular pH

• Proteins in the body regulate the body pH as needed

• Antacids – buffering and non-buffering