Take out your LabTake out your LabStation 6:Station 6:

X- means noX- means nocheck- means yescheck- means yes

Test Unknown #1 Unknown #2 Unknown #3 Unknown #4 Unknown #5 Unknown #6

Cohesion 

           

  Adhesion

           

Solvent

Conclusions (water or not?)

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What is pH?ACIDS & BASES

Journal Week: 3, Tuesday 9/11Journal Week: 3, Tuesday 9/11List 3 items/solutions/foods you believe to List 3 items/solutions/foods you believe to

be acidicbe acidicList 3 items/solutions/foods you believe to List 3 items/solutions/foods you believe to

be basicbe basicEXPLAIN WHY?!EXPLAIN WHY?!Make a “ T CHART” that looks like this:Make a “ T CHART” that looks like this:

AcidsAcids BasesBases

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

Acids and Bases 4

Bitter! Some foods have a Some foods have a

“bite” of their own “bite” of their own because they’re because they’re somewhat bitter.somewhat bitter.

WHY?WHY?

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Acidic/BasicThere 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.Other substances besides foods have Other substances besides foods have

these characteristics. these characteristics.

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Acids and BasesChemicals may be classed as acids or Chemicals may be classed as acids or

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

are are neutralneutral..pHpH measures how acidic or basic a measures how acidic or basic a

solution is.solution is.

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Acids Often taste sour Often taste sour ** Strong acids can burn skin & eyesStrong acids can burn skin & eyes Strong acids can dissolve metalsStrong acids can dissolve metals Examples:Examples:

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

*Never test an unknown acid by tasting it!

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Bases Can taste bitter, sweetish, or salty * Often feel slippery or “soapy” * Strong bases can burn skin & eyes Bases react more easily with protein than

with metal; they are often used for cleaning Examples:

Baking soda Soap Drain cleaner (dangerous!)

*Never test an unknown base by touching or tasting it!

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No I am Not: 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

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Journal Week: 3, Wednesday Journal Week: 3, Wednesday 9/129/12

Get a Green BookGet a Green BookDraw a pH scaleDraw a pH scale

Label: Acid range, Strong Acid, Base range, Label: Acid range, Strong Acid, Base range, Strong base, & neutral.Strong base, & neutral.

pH A special name is A special name is

given to the acid or given to the acid or base characteristic base characteristic that a substance has:that a substance has:

It is called: pHIt is called: pH

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How Do We Measure pH?

We measure pH by We measure pH by using special strips of using special strips of paper called pH paperpaper called pH paper

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How Does It Work? The paper is treated with The paper is treated with

chemicals that change chemicals that change color to show the pH.color to show the pH.

When the paper touches When the paper touches the substance being the substance being tested, it turns a specific tested, it turns a specific color to tell if the color to tell if the substance is an acid or substance is an acid or a base.a base.

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AcidAny substance which has a Any substance which has a pH of value of pH of value of

less than 7 is considered an acidless than 7 is considered an acid

0--------------0--------------7---------------147---------------14 Acid Neutral BaseAcid Neutral Base

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BaseAny substance which has Any substance which has pH value greater pH value greater

than 7 is a basethan 7 is a base

0--------------7-0--------------7---------------14--------------14 Acid Neutral BaseAcid Neutral Base

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pH 7A pH of A pH of 7 is called neutral—neither acid 7 is called neutral—neither acid

nor base.nor base.

0------------0------------77------------14------------14 Acid Neutral BaseAcid Neutral Base

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The pH ScalepH scale ranges from 0 -14pH 7 is neutral; neither acid nor basePure water is pH 7Low pH = acidHigh pH = baseThe closer to the ends of the scale, the

stronger the solution is

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The pH Scale19

The pH Scale Each pH unit is Each pH unit is 1010 timestimes as large as the as large as the

previous oneprevious one A change of 2 pH units means A change of 2 pH units means 100 times100 times more more

basic or acidicbasic or acidic

x10x10 x100x100

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The pH ScaleCareful measurement is importantCareful measurement is importantA mistake of A mistake of oneone pH unit means pH unit means 10 times

too much or too little!too much or too little!

x10x10 x100x100

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Why is pH important?

Soil has to be in a certain pH range for plants to grow and stay healthy.

Fish can’t live if the pH is too high or too low

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pH and People

Water that has too high or low pH may contain harmful dissolved chemicals.

Water plant operators keep a careful watch on the pH of our drinking water, to keep it safe.

Homeostasis

Most Importantly to humans is that the pH within our bodies stays within a certain parameter

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Buffers Buffers The pH of the fluids within most cells The pH of the fluids within most cells

in the human body must generally be in the human body must generally be kept between 6.5 and 7.5.kept between 6.5 and 7.5.

Controlling pH is important for Controlling pH is important for maintaining homeostasis.maintaining homeostasis.

One of the ways that the body One of the ways that the body controls pH is through dissolved controls pH is through dissolved compounds called compounds called buffersbuffers..

BuffersBuffers are weak acids or bases that are weak acids or bases that prevent sharp, sudden changes in pH.prevent sharp, sudden changes in pH.

Two papers, two charts

The yellow paper reads from pH 6.5-13.0 (base). The colors on this side start with yellow (6.5)

The orange paper reads from pH 0-6.0 (acid). Use the side of the dispenser that begins with pH 0.0. It’s easy to recognize because the colors begin with shades of orange.

Using two different papers gives a more precise reading.

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