7th grade scienceWhat is pH?

7th grade scienceWhat is pH?

Some of our Some of our favorite foods favorite foods make our tongue make our tongue curl up because curl up because they are SOUR. they are SOUR.

Acids and BasesAcids and Bases

Bitter!

Some foods have a Some foods have a ““bitebite”” of their own of their own because theybecause they’’re re somewhat bitter.somewhat bitter.

WHY?WHY?

Acidic/Basic

There is a scientific reason for this:There is a scientific reason for this:These foods are either acidic or basic.These foods are either acidic or basic.The degree of acidity or alkalinity (basic) is The degree of acidity or alkalinity (basic) is

important in organisms. important in organisms.

Acids and BasesAcids and BasesChemicals may be classofied as acids or Chemicals may be classofied as acids or

bases.bases.Things that are neither acids nor bases Things that are neither acids nor bases

are neutral.are neutral.pH measures how acidic or basic a pH measures how acidic or basic a

solution is.solution is.

AcidsOften taste sourOften taste sourStrong acids can burn skin & eyesStrong acids can burn skin & eyesStrong acids can dissolve metalsStrong acids can dissolve metalsExamples:Examples:

Lemon juiceLemon juiceVinegarVinegarCar battery acid Car battery acid (dangerous!)

Bases Can taste bitter, sweetish, or saltyCan taste bitter, sweetish, or salty Strong bases can burn skin & eyesStrong bases can burn skin & eyes Bases are often used for cleaningBases are often used for cleaning Examples:Examples:

MilkMilk Baking sodaBaking soda SoapSoap Drain cleaner Drain cleaner (dangerous!)

Some Some substances substances are not really are not really an acid or a an acid or a base: For base: For example, example, pure waterpure water

pH A special name is given to the A special name is given to the

acid or base characteristic that acid or base characteristic that a substance has:a substance has:

It is called: pHIt is called: pH ““pp”” stands for potential and stands for potential and

““HH”” stands for hydrogen; stands for hydrogen; hence, the potential of a hence, the potential of a substance to attract substance to attract hydrogen ionshydrogen ions

Acid

Any substance which has a pH of value of Any substance which has a pH of value of less than 7 is considered an acidless than 7 is considered an acid

Proton donorsProton donors This means that the number of This means that the number of

hydronium (hydronium (HH33O+ )O+ ) ions is greater than the ions is greater than the

number of hydroxide ions number of hydroxide ions (OH-(OH-). ).

0--------------7---------------140--------------7---------------14

Acid Neutral BaseAcid Neutral Base

Base

Any substance which has pH value greater Any substance which has pH value greater than 7 is a basethan 7 is a base

Proton acceptorsProton acceptorsThis means that the number of hydroxide This means that the number of hydroxide

((OH-OH-) ions in a solution is greater than the ) ions in a solution is greater than the number of hydronium (number of hydronium (HH33O+ )O+ ) ions. ions.

0--------------7---------------140--------------7---------------14

Acid Neutral BaseAcid Neutral Base

pH 7

A pH of 7 is called neutral—neither acid A pH of 7 is called neutral—neither acid nor base.nor base.

0------------7------------140------------7------------14

Acid Neutral BaseAcid Neutral Base

The pH Scale Compares the relative Compares the relative

concentration of concentration of HH33O+ ions O+ ions and and OH- ionsOH- ions

Scale ranges fromScale ranges from 0 to 14; 0-3 0 to 14; 0-3 is very is very acidic; 7 is neutral; acidic; 7 is neutral; 11-14 11-14 is very is very basic or basic or alkalinealkaline

Litmus paper, phenolphthalein, Litmus paper, phenolphthalein, pH paper, & other indicators pH paper, & other indicators that change color can be used that change color can be used to measure pH to measure pH

pHpH

Using litmus paper: An acid turns blue Using litmus paper: An acid turns blue litmus paper red and a base turns red litmus paper red and a base turns red litmus paper blue.litmus paper blue.

pH scalepH scale

Scale for Scale for comparing the comparing the relative relative concentrations of concentrations of hydronium ions hydronium ions and hydroxide ions and hydroxide ions in a solutionin a solution

Scale ranges from Scale ranges from 0 to 140 to 14

pHpH

The lower the pH the stronger the acidThe lower the pH the stronger the acid The higher the pH the stronger the baseThe higher the pH the stronger the base pH 7.0 is neutralpH 7.0 is neutral

BuffersBuffers

Control of pH is important Control of pH is important to organisms to organisms

EnzymesEnzymes function only function only within a narrow pH range; within a narrow pH range; usually neutralusually neutral

Buffers Buffers neutralize acids or neutralize acids or bases in organisms to help bases in organisms to help control pH control pH