Download The pH Scale

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Objective: Students will: (1) reflect on Quarter 1 grades and set
goals for Quarter 2; (2)complete word sort to practice
macromolecules; (3) explore pH by creating a foldable.
Catalyst:
1. PREDICT: What do you think pH is?
2. Most carbohydrates in the human body are
A.
B.
C.
D.
used as building blocks for proteins
used as catalysts for reactions in cells
consumed as a source of energy
not easily absorbed into the bloodstream
A.
B.
C.
D.
lipid
amino acid
nucleic acid
carbohydrate
3. A scientist removed the cell membranes from bacteria
cells in a culture. She analyzed the cell membranes for
specific molecules. Which of these was probably the
most common type of molecule present in the bacteria
cell membranes?
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Homework/Reminders:
HW 2.2 and Signed Gradesheet DUE FRIDAY
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Analyze your progress for 1st Quarter
◦ 1. What were the contributing factors to your final
grade?
 HINT: Look at the “Category Summary” at the end of
the gradesheet
◦ 2. What will you do differently for 2nd Quarter?
◦ 3. Write 3 SMART Goals (behavior, academic,
attendance)
 I want to _______________________________________ by
____________(date or time period). I will know that I have
accomplished this goal when I notice/see
_________________________. To make sure I accomplish my goal I
will _____________________________________ (actions).
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Work in your groups to complete the
Macromolecules word sort
What are the four categories?
◦
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Carbohydrates
Lipids
Proteins
Nucleic Acids
Measuring the pH of a solution tells
you whether a solution is an acid or
a base.
 Every molecule in your body works
at a certain pH, so it’s not enough
to know if something is just an acid
or a base—we need to know exactly
how acidic or basic it is so doctors
can keep you healthy!
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 To
do this, we
use something
called the pH
scale.
 The pH scale
goes from zero
to 14.
A pH of less than 7 means acidic and
the lower the pH means the stronger
(or more acidic) the solution is.
 A pH of more than 7 indicates a base
and the higher the pH means the base
is stronger (or more basic).
 In the middle of the scale is pH 7,
which is also called neutral because it
is neither an acid nor a base.
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Use pages 43-44 in your textbook to
complete your foldable
We will go through notes to make sure you
have the correct information in 25 minutes.
Use color! Make sure you include definitions
of key vocabulary words
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“pH” stands for “potential hydrogen.”
◦ It is a measure of the amount of hydrogen ions
dissolved in water
◦ Remember an “ion” is a charged atom
◦ Water can dissolve to form hydrogen (H+ ) and
hydroxide ions (OH- ) H20  H+ + OH-
◦ The pH scale is logarithmic. The calculation is pH =
-log (H+ )
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Acid: a substance that produces hydrogen
ions (H+ ) when dissolved in water
◦ Tastes sour
◦ Turns litmus paper red
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Base: A substance that produces hydroxide
ions (OH- ) when dissolved in water
◦ Also know as alkaline
◦ Tastes bitter
◦ Turns litmus paper blue
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pH affects proteins in the body (ex. Enzymes
that run cell reactions)
◦ Changes in pH (more acidic or more basic) can
denature proteins, causing them to change shape,
making them unable to function normally in the
cell.
 pH
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1
=
Strong Acid
2
Strong Acid
14
Strong base
 pH
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8
=
Weak Base
10
Base
5
Weak Acid
We call tools used to measure pH
indicators because they indicate how
acidic or basic a solution is.
 pH paper will change color when
placed in a solution depending on the
pH of the solution.
 There is a key provided so you can
easily find the pH.
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The pH of solutions can be determined using
 a pH meter
 pH paper
 indicators that have specific colors at
different pH values
15
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Mathematically, pH is the negative log of
the hydronium ion concentration
pH = −log [H3O+]
For a solution with [H3O+] = 1 x 10−4,
pH = −log [1 x 10−4 ]
pH = [4.0]
pH = 4.0
16
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Weak acids or bases that can react with
strong acids or bases to prevent sharp
changes in pH
Blood has a constant pH of around 7.4
◦ Protected by chemical buffers like bicarbonate and
phosphate ion
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Help maintain HOMEOSTASIS
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Applying pH to hair:
◦ Hair is made of PROTEINS
◦ The natural pH of hair is 4.5-5.5
◦ Conditioners smooth and contract the hair shaft using
acid components
◦ Relaxers use strong bases to break bonds and remove
curl
◦ Changing the pH of the solution changes the structure of
the hair
◦ What did we just learn about changing the pH of
proteins?
◦ Why do different hair products have different pH values?
◦ What chemical reaction happens to perm or relax hair?
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Applying pH to food:
◦ Cooking is a series of chemical reactions.
◦ Baking soda and baking powder are leavening agents
added to help baked goods rise (by producing carbon
dioxide gas)
 This is different from yeast because the reaction occurs
based on pH, not the metabolism of sugar
◦ Baking soda is basic and reacts with acidic ingredients
(e.g. yogurt, chocolate, honey, buttermilk, etc)
◦ Baking powder is a combination of ingredients, both
acidic and basic, and is neutral overall in taste
◦ What do baking soda and baking powder do in food?
How are they different?
◦ Why use one instead of another?
1.
2.
Which characteristic of life is affected by
changes in pH?
HSA QUESTION: A scientist believes that a
factory has been dumping acid into a local
river. To test this hypothesis, which
property of water should the scientist
monitor?
A.
B.
C.
D.
Density
pH
Polarity
Temperature