E N V I R O N M E N T A L C H E M I S T R Y A N D O C E A N A C I D I F I C A T I O N

WHAT IS pH?

LESSON 3

LES S O N O BJEC T I VES

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

We are learning about how acids and alkalis are identified using the pH scale.

IDENTIFYwhat the pH

scale is and the purpose for it

1

DETERMINEthe pH of some

everyday substances

2

ANALYZEthe pH of water samples using

universal indicator pa

4

EXPLAINvarious ways to identify the pH of substances

3

LESSON 3 : WHAT IS pH?

K EY VO C ABULAR Y

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

Acid A substance with a pH of less than 7

Alkali A substance with a pH of more than 7 (A soluble base)

Base A substance which can neutralize an acid

Litmus test A test for acidity or alkalinity using litmus

Neutral Solution A substance with the pH of 7

pH A scale (0 -14) which measures the acidity or alkalinity of a solution.

Universal indicator A solution or paper that changes color gradually over a range of pH.This is used to test the acidity and alkalinity of a solution.

LESSON 3 : WHAT IS pH?

S TAR T ER

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

1

Take a look at these four images.

Think about what substances are shown in each image.

How would you categorize these images into two groups?

Why did you choose to organize them this way? Explain.

LESSON 3 : WHAT IS pH?

S TAR T ER

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

1

Acids AlkalisScientists group these substances into acids and alkalis.

Acids are corrosive substances. They are sour to taste.

Alkalis are also corrosive substances. They feel very slippery when touched.

LESSON 3 : WHAT IS pH?

WHAT I S pH?

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

pH is a scale from 0 to 14 that describes how acidic or alkaline a solution is. What is pH?

Using litmus paper or a universal indicator.How can you test pH?

The pH of an acid is less than 7.What is the pH of an acid?

The pH of an alkali is greater than 7. What is the pH of an alkali?

A neutral pH is a solution with the pH of 7. What is a neutral pH?

LESSON 3 : WHAT IS pH?

Litmus paper is used to test whether a solution is acidic or alkaline.

Blue litmus papers turn red in acidic solutions.

Red litmus papers turn blue in alkaline solutions.

Litmus paper does not test how strong an acid or alkali solution is.

L I T MUS P AP ER

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

LESSON 3 : WHAT IS pH?

Universal indicators are more specific than litmus paper. Universal indicators show how strong an acid or alkali is using the pH scale. The colours range from red for strong acids (pH 0) to green for neutral solutions (pH 7) to dark purple for strong alkalis (pH 14).

UN I VER S AL I N D I C AT O R

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

LESSON 3 : WHAT IS pH?

H I GHER O R LO WER pH?

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

Lemonjuice

Stomachacid

MilkBakingsoda

2 1 11 6 9

Ammonia

LESSON 3 : WHAT IS pH?

H I GHER O R LO WER pH?

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

Orangejuice

Acidrain

BleachPurewater

SeaWater

3 4 13 7 8

LESSON 3 : WHAT IS pH?

You have 6 different water samples.

They are:Sea waterRiver waterDistilled waterRain waterAcid rain waterBottled water

Their labels are missing. Your job is to identify each unknown water sample. Most importantly, determine which water sample is the sea water.

I N VES T I GAT I N G THE pH O F WATER

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

LESSON 3 : WHAT IS pH?

I N VES T I GAT I N G THE pH O F WATER

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

Six samples of water labelled A-F

Six test tubes

Test tube holder

Pipette

Universal indicator solution and pH chart

Water sample guide

Equipment

Collect water samples in 6 separate test tubes and place in a test tube rack.

Label each sample A-FUse a pipette to add a small amount of universal indicator into each test tube (a few drops will do)Place a white background behind the test tube. Compare the color of the water sample with the pH chart. Identify the pH for each sample.Compare the pH of each water sample with the water pH guide to identify each unknown sample.

Method

LESSON 3 : WHAT IS pH?

I N VES T I GAT I N G THE pH O F WATER

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

Sample pH Water sample

A 8.1 Sea water

B 7.4 River water

C 7.0 Distilled water

D 5.5 Rain water

E 4.0 Acid rain water

LESSON 3 : WHAT IS pH?

AN S WER S HEET

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

1LESSON 3 : WHAT IS pH?

CHALLEN GE : pH I S A LO GAR I THM I C S CALE

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

LESSON 3 : WHAT IS pH?

The pH scale is logarithmic.

A solution with the pH one less than another is actually 10 times more acidic.

For example:pH 6 is 10x more acidic than pH 7 pH 2 is 10x more acidic than pH 3

Even dropping or increasing the pH by as little as 0.1 makes a big difference because of the logarithmic scale.

R EV I EW

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

Pick three boxes to complete and share your knowledge from today’s lesson.

LESSON 3 : WHAT IS pH?

What is the pH scale a

measure of?

1

Write down two ways to

measure pH.

2

Share two examples of

alkaline solutions.

4

Share two examples of

acidic solutions.

3

What is the pH of seawater?

Distilled water?

5

S ELF AS S ES S MEN T

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y

I can identify what the pH scale is and the purpose for it.ü

I can determine the pH of some every day substances.ü

I can explain various ways to identify the pH of substances.üI can analyze the pH of water samples using universal indicator paper.ü

LESSON 3 : WHAT IS pH?

N EXT LES S O N - O CEAN AC I D I F I CAT I O N

I N P A R T N E R S H I P W I T H S P O N S O R E D B Y