Transcript Acids, Bases, and Indicators

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An acid is a substance that produces hydrogen
ions (H+) when placed in water
o When acids/ ionic compounds are dissolved in
water, the ions split apart from each other
(dissociation)
Photo courtesy of:
http://www.biologycorner.com/worksheets/acids_bases_coloring.html
Most acids…
o Taste sour
o React w/many metals to form H2 gas
o Are corrosive (appears to “eat away”
materials while reacting)
o Have a chemical formula that begins with H
Zinc Metal + Hydrochloric Acid  ??
Zn
(s)
+ 2 HCl
(aq)
 H2 (g) + ZnCl2 (aq)
Predict the type of reaction based on the reactants!
Single-Displacement
Predict the products of this reaction.
Photo Courtesy of:
http://healthmad.com/conditions-and-diseases/the-surprising-health-benefits-of-lemons/
•
Citric Acid
o Found in citrus fruits
• Used as a preservative
•
Lactic Acid
o Found in yogurt
o Produced by our muscles when they are overworked
•
Acetic Acid (HC2H3O2)
o Vinegar
o Used as a preservative
•
Carbonic Acid ( H2CO3) or Phosphoric Acid
(H3PO4)
o Found in soft drinks
•
Hydrochloric Acid (HCl)
o Found in our stomachs- aids in food digestion
Photo Courtesy of:
http://stayinhealth.wordpress.com/2010/02/08/sugary-soft-drinks-increase-pancreas-cancer-risk
A
base is a substance that produces
hydroxide ions (OH-) when placed in
water
• When bases/ ionic compounds are
dissolved in water, the ions split apart
from each other (dissociation)
Photo courtesy of:
http://www.biologycorner.com/worksheets/acids_bases_coloring.html
Most bases…
o Taste bitter
o Feel slippery
o Are corrosive (appears to “eat away” materials
while reacting)
o Have a chemical formula that ends with OH
Photo Courtesy Of:
http://www.pbs.org/wgbh/nova/body/bitter-taste.html
o
Ammonia
• Cleaners and fertilizers
o Sodium hydroxide
• Used in soaps and drain cleaners
o Magnesium hydroxide
• An ingredient found in antacids
Indicators are used to determine if a
substance is an acid or a base
 An indicator changes a specific color when
in the presence of an acid or a base
 Litmus Paper: indicator made of a special filter
paper that contains dyes extracted from lichens
(the crusty “stuff” that grows in rocks)
Blue litmus turns red in an ACID
Red litmus turns blue in a BASE
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Why do you think it’s important to test an unknown
substance with both types of litmus paper?
If one type of litmus paper does not change color, that does not
guarantee that the other type of litmus paper will change color
(i.e. water)
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The pH scale can also help us classify solutions as
acids or bases
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pH is a measure of the amount of H+ ions in a
solution (potential hydrogen)
o The more H+ ions, the lower the pH, the more acidic
the solution
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7 < pH ≤ 14
Complete the following chart by telling whether the pH
represents an acid, base or neutral substance.
Also tell what color each type of litmus paper will turn at
that pH level.
pH
2
8
4
7
13
Acid/Base/Neutral
Color of Blue Litmus Paper
Color of Red Litmus Paper
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When describing acids and bases, strength and
concentration do not mean the same thing!
o Strength refers to the ability of the acid/base to
dissociate in solution
• pH measures this
• Dissociation refers to the ability of an ionic compound to break
apart into ions
o Concentration refers to the amount of acid/base
dissolved in solution.
• An acid or base will have the same pH, regardless of how
concentrated it is
• Just because you add water to dilute it, it’s still going to have the
same amount of H+ ions, they’ll just be spread out more
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When a strong acid/base dissolves
in water, nearly all of the acid/base
molecules will dissociate into ions
Hydrogen
o The greater the ability to dissociate,
the more potential the acid or base has
for being dangerous because there are
more ions available to react
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When a weak acid/base dissolves in
water, only a small fraction of the
acid/base molecules dissociate
(dissociate partially)
o With less ions in solution, there is less
potential for danger because there are
less ions available to react
Hydrogen
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Strong Acids
1. HCl – hydrochloric acid – stomach acid
2. H2SO4 – sulfuric acid – battery acid
3. HNO3 – nitric acid
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Weak Acids:
1. HC2H3O2 – acetic acid – vinegar
2. H3C6H5O7 –citric acid –citrus fruits
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Strong Bases:
1. NaOH – sodium hydroxide
2. Any alkali or alkaline earth metal with OH(i.e. KOH – potassium hydroxide)
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Weak Bases:
1. Al(OH)3 – aluminum hydroxide – often found in
deodorants
2. NH4OH – ammonium hydroxide (ammonia) –
used in many cleaning products
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Neutralization is a chemical reaction between an acid
and a base that takes place in a water solution
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When acids and bases react, the H+ ions from the
acid react with the OH- ions from the base to form
HOH (H2O - water!)
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The overall pH becomes “neutral”
Many people that suffer from heartburn will take antacids to
ease their symptoms (i.e TUMS). How do you think antacids
work?
The stomach is acidic due to HCl and antacids
are basic. A neutralization reaction occurs!
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The ions that are left behind after the H+ and OHions form water, combine to form a salt
o A salt is a compound that forms when the negative ions
from the acid combine with the positive ions from the base
Acid + Base  Water + Salt
HCl(aq) + KOH(aq)  H2O(l) + KCl(aq)
What type of reaction is a neutralization reaction?
Double-Displacement
Name the salt produced in this neutralization reaction.
Potassium chloride
Classify each of the following compounds as an acid,
base or salt.
Then indicate what color each type of litmus paper will
turn when placed in this substance.
Acid/Base/Salt
NaOH
HCl
Ba(OH)2
Al(NO3)3
H2SO4
Color of Blue Litmus Paper
Color of Red Litmus Paper