Acidity, pH, and

Indicators

At this point, you should be familiar with the general properties of acids and bases.

At this point, you should be familiar with the general properties of acids and bases. If not, make sure you review them at this time.

pH of Acidic, Basic, and Neutral

Solutions

The degree of acidity,

The degree of acidity, or how acidic a solution is,

The degree of acidity, or how acidic a solution is, is often represented by a quantity called pH.

The degree of acidity, or how acidic a solution is, is often represented by a quantity called pH. “pH” has a small “p” and a capital “H”.pH is just a number,

The degree of acidity, or how acidic a solution is, is often represented by a quantity called pH. “pH” has a small “p” and a capital “H”.pH is just a number, there is no unit for it.

You should know what the general range in pH is for acidic solutions,

You should know what the general range in pH is for acidic solutions, basic solutions,

You should know what the general range in pH is for acidic solutions, basic solutions, and neutral solutions.

You should know what the general range in pH is for acidic solutions, basic solutions, and neutral solutions. The pH scale diagram in the Science 10 data booklet will help you with this:

You should know what the general range in pH is for acidic solutions, basic solutions, and neutral solutions. The pH scale diagram in the Science 10 data booklet will help you with this:

Let’s have a look at the information in this scale:

Let’s have a look at the information in this scale:

Let’s have a look at the information in this scale:

A Neutral solution has a pH = 7.0

Let’s have a look at the information in this scale:

A Basic solution has a pH >7.0

Let’s have a look at the information in this scale:

Getting more basic

Let’s have a look at the information in this scale:

Getting more acidic

Getting more acidic Getting more basic

Getting more corrosive Getting more corrosive

Getting more corrosive Getting more corrosive

Quite corrosive

Getting more corrosive Getting more corrosive

Quite corrosive

Getting more corrosive Getting more corrosive

Non - corrosive

A More Detailed Look at pH

Like the Richter Scale used for comparing strength’s of earthquakes, the pH scale is a logarithmic scale.

All you are required to know about this here, is that a change of one whole number in pH value represents a ten-fold change in acidity.

10 × more acidic

A solution with a pH of 3 is 10 times more

acidic than a solution with a pH

of 4

A solution with a pH of

2 is 10 times more acidic than a solution with a pH

of 3

10 × more acidic

? × more acidic

How many times more

acidic is a pH of 2 than a

pH of 4?

100 × more acidic

10 × more acidic

10 × more acidic

10

Change to

Scientific Notation100 × more acidic

10 × more acidic

10 × more acidic

Change to

Scientific Notation102 × more acidic

101 × more acidic

101 × more acidic

pHChange in Acidity

Where ΔpH means the change in the value o

0

p

1

f H

pH10

Where ΔpH means the change

Chang

in th

e in Acidit

e value o p

y

f H

pHChange in Acidity 10

Where ΔpH means the change in the value of pH

pH

Where ΔpH means the chang

Change in

e in the

Acid

value

i

t 1

H

y

p

0

of

pH

Where ΔpH means the chang

Change in

e in the

Acid

value

i

t 1

H

y

p

0

of

A solution with a pH of 9 is times (more/less)

acidic than a solution with a pH of 3.

pH

Where ΔpH means the chang

Change in

e in the

Acid

value

i

t 1

H

y

p

0

of

A solution with a pH of 9 is times (more/less)

acidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

pH

Where ΔpH means the chang

Change in

e in the

Acid

value

i

t 1

H

y

p

0

of

A solution with a pH of 9 is times (more/less)

acidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

pH

Where ΔpH means the chang

Change in

e in the

Acid

value

i

t 1

H

y

p

0

of

A solution with a pH of 9 is times (more/less)

acidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

pH

Where ΔpH means the chang

Change in

e in the

Acid

value

i

t 1

H

y

p

0

of

A solution with a pH of 9 is times (more/less)

acidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

pH

Where ΔpH means the chang

Change in

e in the

Acid

value

i

t 1

H

y

p

0

of

A solution with a pH of 9 is times (more/less)

acidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

pH

Where ΔpH means the chang

Change in

e in the

Acid

value

i

t 1

H

y

p

0

of

A solution with a pH of 9 is times (more/less)

acidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

or 1 million

A solution with a pH of 9 is106 times (more/less)

acidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

or 1 million

A solution with a pH of 9 is106 times (more/less)

acidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

or 1 million

?

A solution with a pH of 9 is106 times (more/less)

acidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

or 1 million

The higher the pH of a solution is, the less acidic it is.

A solution with a pH of 9 is106 times lessacidic than a solution with a pH of 3.

pH

6

pH 9 3 6

Change in Acidity 10

10

or 1 million

The higher the pH of a solution is, the more basic, or less acidic it is.

A solution with a pH of 9 is106 times lessacidic than a solution with a pH of 3.

The higher the pH of a solution is, the more basic, or less acidic it is.

A solution with a pH of 9 is106 times lessacidic than a solution with a pH of 3.

The higher the pH of a solution is, the more basic, or less acidic it is.

A solution with a pH of 9 is one million times lessacidic than a solution with a pH of 3.

pHIndicators

A pH indicator is a substance that changes colour when a certain change in pH occurs.

A pH indicator is a substance that changes colour when a certain change in pH occurs.For example, litmus is a familiar indicator.

A pH indicator is a substance that changes colour when a certain change in pH occurs.For example, litmus is a familiar indicator.Paper soaked in litmus is called litmus paper and it is used to test substances to see if they are acidic, basic, or neutral.

There are two main types of litmus paper:

There are two main types of litmus paper: red litmus paper

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus stays red

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus stays red

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red

There are two main types of litmus paper: red litmus paper blue litmus paper

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

Type Add to an Neutral water

red litmus

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Neutral water

red litmus

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Neutral water

red litmus stays red

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Neutral water

red litmus stays red

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Neutral water

red litmus stays red

blue litmus

There are two main types of litmus paper: red litmus paper blue litmus paper

Type Add to an Neutral water

red litmus stays red

blue litmus stays blue

Type Add to an Neutral water

red litmus stays red

blue litmus stays blue

There are two main types of litmus paper: red litmus paper blue litmus paper

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

If we have an unknown solution and we want to find out whether it is acidic, basic, or neutral,

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

If we have an unknown solution and we want to find out whether it is acidic, basic, or neutral, we could dip red and blue litmus paper into it

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

If we have an unknown solution and we want to find out whether it is acidic, basic, or neutral, we could dip red and blue litmus paper into it and from the results and the information below,

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

If we have an unknown solution and we want to find out whether it is acidic, basic, or neutral, we could dip red and blue litmus paper into it and from the results and the information below, we could find out whether it is acidic, basic, or neutral.

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 1 and:

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 1 and: Red litmus paper stays red

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 1 and: Red litmus paper stays red Blue litmus paper stays blue

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 1 and: Red litmus paper stays red Blue litmus paper stays blueThen Unknown 1 is

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 1 and: Red litmus paper stays red Blue litmus paper stays blueThen Unknown 1 is neutral

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 2 and:

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 2 and: Red litmus paper stays red

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 2 and: Red litmus paper stays red Blue litmus paper turns red

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 2 and: Red litmus paper stays red Blue litmus paper turns redThen Unknown 2 is

Adding either type of litmus paper to neutral water will not change its colour.

Type Add to an Acid Add to a Base

red litmus stays red turns blue

blue litmus turns red stays blue

For example, you have a solution called Unknown 2 and: Red litmus paper stays red Blue litmus paper turns redThen Unknown 2 is acidic

Adding either type of litmus paper to neutral water will not change its colour.

Litmus paper is handy for identifying solutions as either acidic, basic or neutral.

Litmus paper is handy for identifying solutions as either acidic, basic or neutral.

Litmus paper is handy for identifying solutions as either acidic, basic or neutral.

Litmus changes colour at a pH of 7

Litmus paper is handy for identifying solutions as either acidic, basic or neutral.

If pH is below 7, litmus is red

Litmus paper is handy for identifying solutions as either acidic, basic or neutral.

If pH is above 7, litmus is blue

Different indicators change colour at different pH values.

Indicators change colour gradually, over a range of pHs.

3.2 4.4

Sloped line between pH = 3.2 and 4.4

Indicators change colour gradually, over a range of pHs.

3.2 4.4

yellowred

Methyl Orange gradually changes from red to yellow between pH = 3.2 to 4.4

Indicators change colour gradually, over a range of pHs.

3.2 4.4

Methyl Orange gradually changes from red to yellow between pH = 3.2 to 4.4

orange yellowred

Indicators change colour gradually, over a range of pHs.

3.2 4.4

Methyl Orange gradually changes from red to yellow between pH = 3.2 to 4.4

orange yellowred

Indicators change colour gradually, over a range of pHs.

3.2 4.4

Methyl Orange gradually changes from red to yellow between pH = 3.2 to 4.4

orange yellowred

Indicators change colour gradually, over a range of pHs.

3.2 4.4

orange yellowred

Methyl Orange gradually changes from red to yellow between pH = 3.2 to 4.4

Methyl Red changes from red to yellow from pH 4.8 to 6.0

Methyl Red changes from red to yellow from pH 4.8 to

6.0

Bromthymol Blue changes from yellow to blue from pH 6.0 to 7.6

Bromthymol Blue changes from yellow to blue from pH 6.0 to

7.6

Using this table, we can see what colours different indicators are at a given pH.

Colours of Various Indicators at a pH of 2

At pH =2: Methyl Orange is red Methyl Red is red Bromthymol Blue is yellow Litmus is red Phenolphthalein is colourless Indigo carmine is blue

Colours of Various Indicators at a pH of 2

At pH =2: Methyl Orange is red Methyl Red is red Bromthymol Blue is yellow Litmus is red Phenolphthalein is colourless Indigo carmine is blue

Colours of Various Indicators at a pH of 2

At pH =2: Methyl Orange is red Methyl Red is red Bromthymol Blue is yellow Litmus is red Phenolphthalein is colourless Indigo carmine is blue

Colours of Various Indicators at a pH of 2

At pH =2: Methyl Orange is red Methyl Red is red Bromthymol Blue is yellow Litmus is red Phenolphthalein is colourless Indigo carmine is blue

Colours of Various Indicators at a pH of 2

At pH =2: Methyl Orange is red Methyl Red is red Bromthymol Blue is yellow Litmus is red Phenolphthalein is colourless Indigo carmine is blue

Colours of Various Indicators at a pH of 2

Colours of Various Indicators at a pH of 11

At pH =11: Methyl Orange is yellow Methyl Red is yellow Bromthymol Blue is blue Litmus is blue Phenolphthalein is pink Indigo carmine is blue

Colours of Various Indicators at a pH of 11

At pH =11: Methyl Orange is yellow Methyl Red is yellow Bromthymol Blue is blue Litmus is blue Phenolphthalein is pink Indigo carmine is blue

Colours of Various Indicators at a pH of 11

At pH =11: Methyl Orange is yellow Methyl Red is yellow Bromthymol Blue is blue Litmus is blue Phenolphthalein is pink Indigo carmine is blue

Colours of Various Indicators at a pH of 11

At pH =11: Methyl Orange is yellow Methyl Red is yellow Bromthymol Blue is blue Litmus is blue Phenolphthalein is pink Indigo carmine is blue

Colours of Various Indicators at a pH of 11

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in bromthymol blue, yellow in methyl red, and blue in indigo carmine. The pH is: a) 4.0 b) 6.0 c) 7.0 d) 8.0

Question: A solution is yellow in methyl orange, pink in phenolphthalein, and green in indigo carmine. The pH is: a) 5.0 b) 6.5 c) 12.5 d) 14.0

Question: A solution is yellow in methyl orange, pink in phenolphthalein, and green in indigo carmine. The pH is: a) 5.0 b) 6.5 c) 12.5 d) 14.0

Question: A solution is yellow in methyl orange, pink in phenolphthalein, and green in indigo carmine. The pH is: a) 5.0 b) 6.5 c) 12.5 d) 14.0

Question: A solution is yellow in methyl orange, pink in phenolphthalein, and green in indigo carmine. The pH is: a) 5.0 b) 6.5 c) 12.5 d) 14.0

Question: A solution is yellow in methyl orange, pink in phenolphthalein, and green in indigo carmine. The pH is: a) 5.0 b) 6.5 c) 12.5 d) 14.0

Question: A solution is yellow in methyl orange, pink in phenolphthalein, and green in indigo carmine. The pH is: a) 5.0 b) 6.5 c) 12.5 d) 14.0