acidity, ph, and indicators. at this point, you should be familiar with the general properties of...

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:

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


A Neutral solution has a pH = 7.0


A Basic solution has a pH >7.0


Getting more basic


Getting more acidic

Getting more acidic Getting more basic

Getting more corrosive Getting more corrosive


Quite 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


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


Change in

e in the

Acid

value

i

t 1

H

y

p

0

of



pH

6

pH 9 3 6

Change in Acidity 10

10

pH


Change in

e in the

Acid

value

i

t 1

H

y

p

0

of



pH

6

pH 9 3 6


10

or 1 million

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


pH

6

pH 9 3 6


10

or 1 million



pH

6

pH 9 3 6


10

or 1 million

?



pH

6

pH 9 3 6


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


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 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



red litmus stays red

blue litmus



red litmus stays red turns blue

blue litmus




blue litmus turns red





blue litmus turns red stays blue

Type Add to an Neutral water

red litmus

blue litmus




blue litmus





blue litmus stays blue



blue litmus stays blue


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




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





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





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,





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.





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





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





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





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





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





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





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





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





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


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


Litmus changes colour at a pH of 7


If pH is below 7, litmus is red


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


3.2 4.4

yellowred

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


3.2 4.4


orange yellowred


3.2 4.4

orange yellowred


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


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


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

acidity, ph, and indicators. at this point, you should be familiar with the general properties of...

Documents

ph slide

acidic slide

ph of acidic

basic slide

corrosive slide

ph value

acidic solutions

ph scale diagram