Transcript Preparing red cabbage pH papers.

Acids and Bases Everywhere

Every liquid you see
will probably have
either acidic or basic
traits. One exception
might be distilled
water. Distilled water
is just water. That's it.
The positive and
negative ions in
distilled water are in
equal amounts and
cancel each other out.
Acids and Bases Everywhere

Those ions in solution make something acidic or
basic. In your body there are small compounds
called amino acids. Those are acids. In fruits
there is something called citric acid. That's an
acid, too. But what about baking soda? When
you put that in water, it creates a basic solution.
Vinegar? Acid.
PH Scale
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Scientists use something called the pH scale to
measure how acidic or basic a liquid is.
Although there may be many types of ions in a
solution, pH focuses on concentrations of
hydrogen ions (H+) and hydroxide ions (OH-).
PH Scale
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The scale goes from values very close to 0
through 14. Distilled water is 7 (right in the
middle). Acids are found between a number
very close to 0 and 7. Bases are from 7 to 14.
Most of the liquids you find every day have a pH
near 7. They are either a little below or a little
above that mark.
PH Scale
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When you start looking at the pH of chemicals,
the numbers go to the extremes. If you ever go
into a chemistry lab, you could find solutions
with a pH of 1 and others with a pH of 14.
There are also very strong acids with pH values
below one such as battery acid. Bases with pH
values near 14 include drain cleaner and
sodium hydroxide (NaOH). Those chemicals
are very dangerous.
Names to Know
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Acid: A solution that has an excess of H+ ions. It comes from the Latin
word acidus that means "sharp" or "sour".
Base: A solution that has an excess of OH- ions. Another word for base
is alkali.
Aqueous: A solution that is mainly water. Think about the word
aquarium. AQUA means water.
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Strong Acid: An acid that has a very low pH (0-4).
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Strong Base: A base that has a very high pH (10-14).
What really happens..

If you have an ionic compound and you put it in
water, it will break apart into two ions. If one of
those ions is H+, the solution is acidic. If one of
the ions is OH-, the solution is basic.
What really happens..

That pH scale we talked about is
actually a measure of the number
of H+ ions in a solution. If there are
a lot of H+ ions, the pH is very low.
If there are a lot of OH- ions, that
means the number of H+ ions is
very low, so the pH is high.
Acid or Base?
Acids and Bases
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Acids are substances which free hydrogen ions
(H+), when they are mixed with water. Bases are
substances which free hydroxide ions (OH-)
when they are mixed with water.
Acids and Bases
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Substances with pH lower than 7 are considered
acids, those with pH equal to 7 are considered
neutral, and those with pH higher than 7 are
considered bases. .
How to Measure PH
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Litmus Paper
Litmus Paper
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Litmus is a substance obtained from certain
lichens. It has the property of changing its color
to red with acidic substances and to blue with
basic ones. On the packet of the litmus paper,
there is a color scale which indicates the color
assumed by the paper as a function of the pH
pH Meter
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The pH meter is an electronic
instrument supplied with a special bulb
which is sensitive to the hydrogen ions
which are present in the solution being
tested.
The signal produced by the bulb is
amplified and sent to a liquid-crystal or
an analog meter display.
These instruments are much more
precise and convenient to use than the
indicating papers
Red Cabbage Juice

As we have seen, acids and
bases have the property of
modifying the color of certain
substances. This is the case
with the juice of the red
cabbage. This liquid has a
blue-violet color, but when it
comes in contact with acidic
substances it becomes red,
while in contact with basic
substances it becomes green
and even yellow.
Red Cabbage Juice
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Red cabbage juice mixed with baking soda (left)
and with vinegar (right).
On the top, a drop of unmixed juice.
Preparing red cabbage pH papers.
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Soaking cards with red cabbage juice..
Preparing red cabbage pH papers.
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Drying the cards.
Preparing red cabbage pH papers.
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Cutting the strips
Preparing red cabbage pH papers.
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Lemon Juice
Baking soda
Color of the scale in cabbage papers
Properties of Acids
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Corrosive ('burns' your skin)
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Sour taste (lemons, vinegar)
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Contains hydrogen ions (H+) when dissolved in
water
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Has a pH less than 7
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Turns blue litmus paper to a red color
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Reacts with bases to form salt and water
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Reacts with metals to form hydrogen gas
Examples of Acids
* Hydrochloric acid (HCl) in gastric juice
* Sulphuric acid (H2SO4)
* Carbonic acid in softdrink (H2CO3)
* Uric acid in urine
* Ascorbic acid (Vitamin C) in fruit
* Citric acid in oranges and lemons
* Acetic acid in vinegar
* Tartaric acid (in grapes)
Examples of Bases
* Sodium hydroxide (NaOH) or caustic soda
* Calcium hydroxide ( Ca(OH)2 ) or limewater
* Ammonium hydroxide (NH4OH) or ammonia
water
* Magnesium hydroxide ( Mg(OH)2 ) or milk of
magnesia
* Many bleaches, soaps, toothpastes and cleaning
agents
Properties of Bases
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Soapy feel
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Has a pH more than 7
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Turns red litmus paper to a blue color
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Many alkalis (soluble bases) contain hydroxyl
ions (OH-)
Reacts with acids to form salt and water
HOMEWORK
Every team must
bring the
following:
1. Lemon
I need ONLY 1
person to bring
the following:
1. Egg
2. Mayonnaise
2. Slice of white
bread
3. Mustard
3. Apple
4. Ketchup
4. Orange
HOMEWORK
I will bring the following:
1. Baking soda
2. Vinegar
3. Bathroom cleaner
4. Vinegar
5. Hydrochloric Acid
6. Sugar