Unit 5 Lesson 3 Measuring pH
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Unit 5 Lesson 3 Measuring pH
What’s Your Number?
What is the pH scale?
• The pH of a solution is a measure of how acidic or
basic a solution is. A solution that has a pH value
of exactly 7 is neutral—neither acidic nor basic.
• A solution with a pH value of less than 7 is acidic.
There are more H3O+ ions than OH– ions in the
solution.
• A solution with a pH value greater than 7 is basic.
There are more OH– ions than H3O+ ions in the
solution.
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Unit 5 Lesson 3 Measuring pH
What is the pH of some common
solutions?
• Lemon juice has a pH of about 2. Milk has a pH of
about 6.5, but sour milk has a pH of about 4.
• Pure water is neither acidic nor basic; it is neutral.
It has a pH of 7.
• A solution of ammonia has a pH of around 12.
Antacid tablets dissolve in water to form a basic
solution of about pH 8.
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Unit 5 Lesson 3 Measuring pH
What is the pH of some common
solutions?
• Locate lemon juice, milk, pure water, and
ammonia on the pH scale.
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Unit 5 Lesson 3 Measuring pH
How is pH measured?
• An acid-base indicator is a dye that changes color
at a certain pH range. The pH can be estimated by
placing a few drops of indicator in a solution.
• The pH of a solution can be checked by placing a
drop of the solution on a strip of universal pH
paper, which contains several acid-base indicators.
• An electronic pH meter has a probe that is placed
into the solution being measured. A precise pH
value is measured.
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Unit 5 Lesson 3 Measuring pH
A Natural pH Meter
• Hydrangea plants act as acid-base indicators in
nature. The flowers change color depending on
the pH of the soil.
• Pink flowers indicate that the soil pH is greater
than 6.5. It is basic.
• Blue flowers indicate that the soil pH is less than
5.5. It is acidic.
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Unit 5 Lesson 3 Measuring pH
In Our World
What role does pH play in the
environment?
• If soil pH is too acidic or too basic, the nutrients
plants need do not dissolve into the water in the
soil.
• As a result, plants do not grow well, and the
animal population that depends on the plants also
suffers.
• The pH of ocean water is usually about 8. If the
water absorbs too much carbon dioxide, the pH
may be lowered, harming sea animals.
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Unit 5 Lesson 3 Measuring pH
What role does pH play in the
environment?
• How would a decrease in soil pH affect the
ecosystem shown?
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Unit 5 Lesson 3 Measuring pH
What causes acid rain?
• Acid rain is any form of precipitation, such as rain,
sleet, or snow, that has a lower pH than the
normal range between 5 and 6.
• The burning of fossil fuels releases sulfur oxides
and nitrogen oxides, which combine with water in
the air to produce sulfuric acid and nitric acid.
• These acids in the atmosphere form acid rain
when they dissolve in precipitation such as
raindrops.
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Unit 5 Lesson 3 Measuring pH
What are the effects of acid rain?
• Acid rain can lower the pH of lakes, ponds, and
streams, harming aquatic species and other
organisms that rely on the water for survival.
• Acid rain can harm plants by damaging their
leaves.
• It can also harm plants and other living things by
lowering soil pH.
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Unit 5 Lesson 3 Measuring pH
What are the effects of acid rain?
• Acid rain can damage buildings and sculptures
made of limestone and marble, by reacting with
the stone.
• Acid rain can also damage paint and cause metals
to corrode faster.
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Unit 5 Lesson 3 Measuring pH
Body in Balance
Where does pH play an important role
in the human body?
• Stomach pH is usually about 2.5. But if food that
is difficult to digest is eaten, more stomach acid is
made and the acidity can drop as low as 1.2.
• Difficulty digesting food and a low stomach pH can
cause discomfort called indigestion.
• Stomach pH can be restored back to a normal
level by consuming antacid tablets, which are
basic.
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Unit 5 Lesson 3 Measuring pH
Where does pH play an important role
in the human body?
• To maintain good health, blood pH needs to be
between 7.35 and 7.45.
• If blood pH falls below 7.35, it is too acidic. This
condition is called acidosis.
• If blood pH rises above 7.45, it is too alkaline.
This condition is called alkalosis.
• Both conditions make a person feel ill.
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Unit 5 Lesson 3 Measuring pH
Where does pH play an important role
in the human body?
• How does blood pH affect a person’s health?
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