Acids and BasesA Short Introduction

Acids and Bases Are Everywhere• Look around you and every

liquid you see will probably be either an acid or a base.

• The only exception would be distilled water. Distilled water is just water. That's it.

• Most water you drink has ions in it. It is those ions (H+ or OH-) which make something acidic or basic.

• In your body there are small compounds called Amino Acids. Those are acids.

• In fruits there is something called Citric Acid. That’s an acid too.

• When you put baking soda in water it makes a base.

• Vinegar is an acid. It is a weak solution of Acetic Acid in water.

Acids and Bases Are Everywhere

pH Scale• Scientists use something called the

"pH" scale to measure how acidic or basic a liquid is.

• The scale goes from “1" to "14". Distilled water is 7 (right in the middle).

pH ScaleAcids are found between “1" and “6". Bases are from “8" to "14".Most of the liquids you find every day have a pH near "7", either a little below, or a little above.When you start looking at the pH of chemicals the numbers go to the extremes.If you ever go into a chemistry lab, you could find solutions with a pH of "1" and others with a pH of "14". Those chemicals are very dangerous.

A Quick Comparison of Acids and Bases

The name acid comes from the Latin word acidus, which means “sour”.When dissolved in water, acids have a sour taste.Acids cause the dye in litmus paper to change from blue to red.

Water solutions of base feel slippery or soapy to the touch.When fatty substances are placed in a base solution, they dissolve.Bases cause the dye in litmus to change from red to blue.Household cleaning products contain a base.

What Really Happens?A Little Tricky, but Here Comes the Straight Answer.

Acid Vs. BaseAcids are compounds which

break into hydrogen (H+) ions and another compound when placed in an aqueous solution (water).

Bases are compounds which break up into hydroxide (OH-) ions and another compound when placed in an aqueous solution (water).

One More Time…• If you have an IONIC compound and

you put it in water it will break apart into two ions.

• If one of those ions is H+ … The solution is acidic.

• If one of the ions is OH- … The solution is basic.

• There are other ions which make acidic and basic solutions, but we won’t be talking about them here.

pH Scale… One More Time• The pH scale we talked about is

actually a measure of the number of H+ ions in a solution.

• If there are a lot of H+ ions, the pH is very low.

• If there are a lot of OH- ions, that means the number of H+ ion is very low, so the pH is high.

Vocabulary to KnowACID = a solution that has an excess of H+ ions.BASE = A solution that has an excess of OH- ions. Another word for base is ALKALI.AQUEOUS = A solution which is mainly water. Think of the word aquarium.STRONG ACID = An acid which has a very low pH (1-4).STRONG BASE = A base which has a very high pH (11-14).

More Vocabulary to KnowWEAK ACID = An acid that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (5-6).WEAK BASE = A base that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (8-10).NEUTRAL = A solution which has a pH of 7. It is neither acidic or basic.

Examples of

Acids and Bases

NaOH (Sodium Hydroxid

e)

KOH (Potassi

um Hydroxid

e)

H2SO4

(Sulfuric Acid)

HCl

(Hydrochloric Acid)

HC2H3O2

(Acetic Acid)

HNO3

(Nitric Acid)

Examples of Acids and Bases

Acid-Base Indicators• An acid-base indicator is a weak

acid or a weak base.• Indicators are substances that

change color depending on whether the solution is acid or alkaline.

• You need to know the names and colors of some common indicators.

Acid-Base Indicators• An indicator does not change color

from pure acid to pure alkaline (basic) at specific hydrogen ion concentration, but rather, color change occurs over a range of hydrogen ion concentrations.

• This range is termed the color change interval. It is expressed as a pH range.

Common IndicatorsLitmus, red in acid solution, blue in alkaline solution.

Phenolphthalein, colorless in acid solution, pink in alkaline solution.

Universal indicator, has a range of colors depending on the strength of the acid or alkali.

pH Numbers of ‘Everyday’ Substances

Dilute hydrochloric acid, 1.5 Lemon juice, 2.5 Orange juice, 3.5 Pure water, 7.0 Blood, 7.5 Milk of magnesia, 10.5 Dilute sodium hydroxide, 13.0

It’s Your Turn!Were You Sleeping on the Job?

A substance that exhibits a sour taste.

A substance that exhibits a bitter taste.

A substance that reacts with metals to produce hydrogen gas.

A substance that feels slippery to the touch because it dissolves the surface of the skin.

Quick Quiz

Quick Quiz ContinuedA substance that has a pH of greater than 7. A substance that has a pH of less than 7. A substance which turns blue litmus paper red or cause no change to red litmus paper. A substance which turns red litmus paper blue or cause no change to blue litmus paper.

That’s basically it. (Ha Ha, get it?)