Download Science 11th grade LEARNING OBJECT Why are carboxylic acids

Science 11th grade
LEARNING UNIT
What is everything around
us made of?
S/K
Language
Socio cultural context of
the LO
Curricular axis
Standard competencies
Background Knowledge
English Review topic
Vocabulary box
LEARNING OBJECT
Why are carboxylic acids weak acids?
SKILL 1: Recognize the carboxyl functional group and the
spatial dissociation of atoms.
SKILL 2: Investigate the acetic acid dimer and its relationship
with intermolecular attractive forces.
SKILL 3: Identify the functional groups that present chemical
reactions of nucleophilic substitution on carboxylic acids, and
explains these reactions.
SKILL 4: Recognize and explains chemical neutralization
reactions between a carboxylic acid and a strong base.
SKILL 5: Order the carboxylic acids according to their acidity.
SKILL 6: Compare the boiling point, reactivity, water solubility
and alcohols of the carboxylic acid derivatives.
SKILL 7: Look into and speaks about the applications of
carboxylic acids and their derivatives.
English
Colombia
Living environment
I relate functional groups to the physical and chemical
properties of substances.
Nomenclature of alkanes, molecule, bonds, organic
molecules, boiling point, weak and strong acids.
Relative clauses (which, that)
Bridge (noun): a structure that is built over a river, road, or
railway to allow people and vehicles to cross from one side to
the other.
Chemical bond (noun): an electrical force that holds atoms
together to form a molecule.
Dimer (noun): a compound formed by the union of two radicals
or two molecules of a simpler compound.
Join (verb): to connect or fasten things together.
Dissociation (noun): the process by which a chemical
combination breaks up into simpler constituents.
Main (adjective): larger, more important, or having more
influence than others of the same type.
Catalyst (noun): something that makes a chemical reaction
happen more quickly without itself being charged.
Protonate (transitive verb): to add a proton to.
NAME: _________________________________________________
GRADE: ________________________________________________
Introduction
What do these things have in common?
Figure. Example of carboxylic acids present in fruits, food and animals.
Swiss cheese: its characteristic smell is due to propionic acid. During the ripening process,
microorganisms like Propionibacterium shermanii convert lactic acid and lactates to
propionic and acetic acid, and CO2. (Netto, 2011).
Sweat: the odor of human sweat is due mainly to (E)-3-methyl-2-hexenoic and butyric acid.
(Navarro, n.d.).
Citruses: citric acid is responsible for the smell and acidity of acidic fruits like lime and
orange. (Netto, 2011).
Vinegar: it is also called 5% acetic acid.
Why do you feel a sting when an ant bites you?
A way of defense in ants is injecting formic acid when they bite.
Palm oil: its main component is palmitic acid. This is the second oil with most production in
the world. Colombia and Ecuador are the countries that produce it the most in Latin
American. (Wikipedia collaborators, 2016).
Objectives



To interpret some of the physical and chemical properties of carboxylic acids
and their derivatives.
To explain the physical properties of carboxylic acids.
To recognize the applications of the most common carboxylic acids.
Activity 1
Skill 2 Investigates the acetic acid dimer and its relationship with intermolecular attractive
forces.
Skill 5 Orders the carboxylic acids according to their acidity.
Skill 7 Looks into and speaks about the applications of carboxylic acids and their derivatives.
What are carboxylic acids?
They are the most abundant organic compounds in living organisms. You can also find them
in a chemical laboratory.
Carboxylic acids are weak acids; they contain a carboxyl functional group (COOH).
(McMurry & Simanek, 2007).
Many of the names of the most common carboxylic acids are related to their history. For
example, formic acid is extracted from ants. Its name comes from the Latin word Formica,
which means ant (Brown et al., 2004). Meanwhile, the name of aspirin derives from the
chemical substance called acetylsalicylic acid, which is acetylspirsäure in German.
Figure. Molecular structure of aspirin.
Acetylsalicylic acid has been one of the most commonly used analgesics for thousands of
years, even before Christ. Hippocrates was one of the first people to use it for soothing pain
and fever. He observed that a bitter powder with analgesic properties could be obtained from
the bark of the willow tree.
Later, in the 19th century, chemist Charles-Frédéric Gerhardt discovered its formula and
chemist Felix Hoffman, who worked for the Bayer pharmaceutical company, obtained the
compound more easily and on a large scale. On March 5, 1899, Bayer named this medicine
aspirin (Roca, 2003).
Did you know that…?
Carboxylic acids are present in many types of food and used in the industry for elaborating
fibers and paint. (Brown et al., 2004).
Search 4 carboxylic acids used for elaborating fibers or paint. Draw their molecular formulas
and present them in class.
Which are their physical properties?

They are polar given the double bond between carbon and oxygen, and the
hydroxyl group connected through hydrogen bridges.

Carboxylic acids smaller than 4 carbons are water-soluble. This is due to the
interactions between acid and water (Fernández, 2014). The carboxylic acid
derivatives are soluble in esters, alkanes, and aromatic hydrocarbons (Bruice,
2007).

Many carboxylic acids form dimers when they are pure or in dissolution. The
dimers are joined by two hydrogen bonds; an example is acetic acid.
Figure. Representation of the formation of dimers in the acetic acid. (McMurry & Simanek, 2007).
Strong hydrogen bonds are related to the boiling point, which is greater than that of alkanes
or alkyl halides of similar molecular weight. For example, the boiling point of acetic acid is
118º C and that of chloropropane (alkane) is 46.6º C. (McMurry & Simanek, 2007).

The boiling point of carboxylic acids is relatively high, because they form
intermolecular (between molecules) hydrogen bridges.
So, the boiling point, compared to other compounds (Bruice, 2007):
Amide > carboxylic acid >> ester ≈ acyl chloride ≈ aldehyde ≈ ketone
Answer the following question:
What is the relationship between the formation of dimers in acetic acid and the
intermolecular attractive forces?
Acidity
The acidic behavior of carboxylic acids is given by the hydrogen of the hydroxyl group, which
has a relatively low pKa value from 4 to 5. This causes the carbonyl group to be
electronegative.
Carboxylic acids are more acidic than alcohols, since electronegative groups increase
acidity, stealing charge by inductive effect (Fernández, 2014).
The protons that come from the dissociation of a carboxylic acid are greater than those of
an alcohol, since a conjugate base is more stable with an acid than with an alcohol.
Additionally, the pKa value can decrease when halides are added to the carbon chain.
Taking the above into account, the table shows carboxylic acids that contain strong and
weak acids.
Table. Strong acids of some carboxylic acids. (McMurry & Simanek, 2007).
Carboxylic acids are acids because the negative charge of the carboxylate ion is delocalized
via resonance; in other words, the electrons are distributed homogenously in the molecule.
When a group reduces the effect of the negative charge, the carboxylic acid is more acidic.
The groups that attract electrons (F>Cl>Br>I) increase the acidity because they reduce the
negative charge. Also, the more
electron-attracting substituents the compound has, the higher the acidity.
The electron-donating groups, like the methyl group, reduce acidity because they increase
the negative charge (Bailey & Bailey, 1998).
Example:
ICH2CO2H
CH3CO2H
pKa 3.17
pKa 4.75
Remember that… the halogen I increases the acidity of a carboxylic acid.
Watch the following video to understand much better:
[Khan Academy]. (2010, octubre 20). Carboxylic Acid Naming
[Video File]. Retrieved from: https://www.youtube.com/watch?v=xheOq0XZ-so
Learning activity 1
1. Answer whether each statement is true (T) or false (F):
a)
b)
c)
d)
Carboxylic acids have a carboxyl functional group in a primary carbon.
The carboxylic acid found in human sweat is formic acid.
The acetic acid in aqueous solution is known as aspirin.
If an acid that is part of a carboxylic acid has a pKa value of 0= 1, it is a strong
acid.
e) The boiling point of a carboxylic acid is greater than that of an aldehyde.
f) The boiling point of carboxylic acids is greater than that of an ester and lower
than that of an amide.
2. Based on the acidity of the compounds, complete the following table by listing them from
the least acidic to the most acidic (1 to 5):
pKa
Compound
4.76
3.75
2.90
2.59
0.63
Activity 2
Skill 1 Recognizes the carboxyl functional group and the spatial dissociation of atoms.
Scene 1
Did you know that most of the food we consume daily is made up of proteins?
Scene 2
Student: Are proteins important?
Teacher: They are vital for the human body and its functions; they are sources of energy.
Proteins allow us to carry out our daily activities.
Scene 3
What is the structure of a protein?
The primary structure of a protein is composed of amino acids, which are joined through
peptide bonds. Its structure becomes more complex as it forms hydrogen bonds and
interacts with the environment. Its final structure is tridimensional.
Scene 4
Do you know what amino acids have in common?
They are made up of a carboxyl group!
How are carboxylic acids named?
They are named by substituting the –e ending of the alkane’s name with “-oic acid”. (Bruice,
2007).
Example:
Figure. Molecular structure of the methanoic acid.
The position of a substituent is designated by a number, in which carboxylic carbon is always
carbon 1. (Bruice, 2007).
Figure. Examples of how to enumerate the carbons of a carboxylic acid.
Very important…
The nomenclature of alkanes is useful for naming carboxylic acids.
Table. Nomenclature of some straight-chain alkanes.
A compound that has a COOH group connected to a ring is named with the suffix “carboxylic
acid”. (McMurry & Simanek, 2007).
Figure. Example of a cyclic carboxylic acid.
Learning activity 2
1. Name the following compounds and indicate which carbon has the carboxyl group.
A
B
C
Activity 3
Skill 3 Identifies the functional groups that present chemical reactions of nucleophilic
substitution on carboxylic acids, and explains these reactions.
Skill 4 Recognizes and explains chemical neutralization reactions between a carboxylic acid
and a strong base.
Skill 6 Compares the boiling point, reactivity, water solubility and alcohols of the carboxylic
acid derivatives.
Do you know that we can identify if a sample contains carboxylic acids in the
laboratory? (Carrascal, n.d.).
Figure. Production of acetic acid from ethanol, through oxidation. (O) corresponds to any type of
oxidizing agent. (Brown et al., 2004).
How is a carboxylic acid obtained?
Oxidation:
We can obtain carboxylic acids from two alcohols in which the hydroxyl group is connected
to a CH2 such as ethanol. If an oxidizing agent like K2Cr2O7 is used, an acetaldehyde is
produced in the first reaction, and then acetic acid is generated. (Brown et al., 2004).
Let’s observe an example:
Figure. Production of an acetic acid from ethanol, through oxidation. (O) corresponds to any type of
oxidizing agent. (Brown et al., 2004).
Can carboxylic acids form salts?
Carboxylic acids form salts through a neutralization reaction. A carboxylic acid can react
with a strong base like NaOH. (McMurry & Simanek, 2007).
Figure. Neutralization reaction of a carboxylic acid to form salts. (Hopp, 1994).
Carboxylic acid derivatives
These are compounds in which the hydroxyl group is replaced by another group. (McMurry
& Simanek, 2007).
Figure. Carboxylic acid derivatives.
What do you know about the nucleophilic substitution reactions?
The main characteristic that carboxylic acids have, which distinguishes them from aldehydes
and ketones, is that they form their derivatives through a nucleophilic substitution reaction.
How does this happen? Basically, the hydroxyl group is replaced with a basic one.
(Lamarque, 2008).
Carboxylic acids can only experiment this type of reaction in their acid forms. They can react
with alcohols to form esters. Emil Fischer discovered that one could obtain an ester by
treating a carboxylic acid with an excess of alcohol, in the presence of an acid catalyst. For
this reason, this reaction receives the name of Fischer esterification. (Bruice, 2007).
Figure. Reaction mechanism of Fischer esterification of a carboxylic acid.
1. The carboxylic acid is activated by the protonation of the oxygen atom of the
carbonyl group.
2. The nucleophilic attack of alcohol takes place, and a tetrahedral intermediate
is formed.
3. The transference of a proton from an oxygen to another produces a second
tetrahedral intermediate and liberates the OH.
4. In the elimination of water, a proton regenerates the acid catalyst and an ester
is obtained.
Is the reactivity of the carboxylic acid derivatives similar?
The order of the reactivity of these compounds is related to the electronegativity and the
basicity of the substituent group. (McMurry & Simanek, 2007).
Figure. Relationship between the reactivity of a carboxylic acid derivative and the basicity of the
substituent group. (Veliz, 2013).
Taking into account the information above, complete the table and compare the boiling point,
the reactivity (from more reactive to less reactive 1-3), and the solubility of the following
carboxylic acid derivatives:
Name
CH3CONH2.
Acetamide
CH3COCl
Acetyl chloride
CH3CH2COOCH2CH(CH3)2
Isobutyl Propionate
Learning activity 3
Boiling
point
Solubility
51oC
Reactivity
1
Ethanol
1. Choose which of the following reactions correspond to nucleophilic substitution reactions:
A
B
Match the concepts in the left column to the content in the right column. You must drag the
concept (left side) and drop it on the content (right side)
1 A neutralization reaction
occurs…
2 Formation of esters from
carboxylic acids.
3 The Fischer reaction
produces…
4 You can detect a carboxylic
acid by adding…
5 A nucleophilic substitution
reaction doesn’t occur…
6 Formation of carboxylic acids.
A in a basic medium.
B bicarbonate of soda.
C ester and water.
D
Nucleophilic
substitution
reaction.
E Oxidation of a primary alcohol.
F adding a strong base.
Explain in your own words, in your notebook, how carboxylic acids are related to the
neutralization and nucleophilic substitution reactions.
Summary

Carboxylic acids are known for having a carboxyl functional group (COOH).

Many carboxylic acids form dimers that are joined by hydrogen bonds.

The boiling point of carboxylic acids is relatively high because they form hydrogen
bridges.

The carboxylic acids are named by replacing the –e ending with “-oic acid”.

A carboxylic acid can be obtained through the oxidation of primary alcohols.

Carboxylic acids can form salts through a neutralization reaction.

Carboxylic acids can form derivatives through the nucleophilic substitution reaction.
Homework
1. Form a group of 5 people.
2. In group, pick one of the following carboxylic acids:







Benzoic acid
Acetic acid
Formic acid
Butanoic acid
Acetylsalicylic acid
Linoleic acid
Fumaric acid
3. Using recyclable material, build a 3D model of the molecular structure.
4. Each group will have 15 minutes to present their model and explain the following:







Molecular weight
Boiling point
pKa
pH
Where the carboxylic acid comes from
Uses
Derivatives of this carboxylic acid
5. The class must organize the reviewed carboxylic acids according to their acidity (from
strong to weak), boiling point, and molecular weight.
Evaluation
To take this evaluation, you must complete the entire learning object.
True or false questions:
1. The functional group of the carboxylic acid is a hydroxyl group on the secondary carbon.
2. The boiling point is related to the number of hydrogen bridges that are formed.
3. An alcohol is more acidic than a carboxylic acid.
4. Fischer’s reaction forms an ester from a carboxylic acid, through nucleophilic substitution.
Multiple-choice questions with one answer:
5. When you add a strong base to a carboxylic acid, you form:
A an alcohol
B an ester
C a salt
D an amide
6. An acid of 7 carbons can be called a:
A Hexanoic acid
B Butanoic acid
C Heptanoic acid
D Propanoic acid
7. Acetic acid forms dimers, which are joined by:
A Hydrogen bonds
B Covalent bonds
C Metallic bonds
D Polar covalent bonds
Complete the following sentences:
8. Oxalic acid has a pKa of 1.25. This means that it is a _______ acid.
9. Fischer’s reaction begins with the ______ ______ by the ______ _______ of the carbonyl
group’s oxygen.
Bibliography
Bailey, P. S., & Bailey, C. A. (1998). Química orgánica: conceptos y aplicaciones (Vol. 2).
Pearson Educación.
Brown, T. L., LeMay, H. E., Jr., Bursten, B. E., & Burdge, J. R. (2004). Química. Pearson
Educación.
Bruice, P. Y. (2007). Fundamentos de Química Orgánica. México: Pearson Education.
Carrascal, D. (n.d.). Algunas reacciones de ácidos carboxílicos y sus derivados. Retrieved
from:
http://www.academia.edu/8555262/Algunas_reacciones_de_%C3%81cidos_Carbox
%C3%ADlicos_y_sus_derivados
Colaboradores de Wikipedia. (2016). Aceite de palma - Wikipedia, la enciclopedia libre.
Retrieved from: https://es.wikipedia.org/wiki/Aceite_de_palma
Fernández, G. (2014). Química Orgánica. Germán Fernández. Retrieved from:
https://books.google.com/books?id=uhXGAgAAQBAJ&pgis=1
Hopp, V. (1994). Fundamentos de tecnología química. Reverte.
Lamarque, A. (2008). Fundamentos teorico-practicos de química orgánica/ Theoretical and
practical organic chemistry. Editorial Brujas.
McMurry, J. E., & Simanek, E. (2007). Fundamentals of Organic Chemistry (6th ed.).
Thomson.
Navarro, E. T. (n.d.). Ácidos carboxilicos. Retrieved from: http://acidoscarb.blogspot.es/
Netto, I. R. C. M. (2011). Ácidos orgánicos presentes en la vida cotidiana. Retrieved from:
http://www.alimentacion.enfasis.com/articulos/19261-acidos-organicos-presentes-lavida-cotidiana
Roca, A. J. (2003). Historia de los medicamentos. Academia Nal. de Medicina.
Veliz, L. M. F. (2013). Derivados funcionales de los ácidos carboxílicos. Retrieved from:
http://es.slideshare.net/lfelix/derivados-funcionales-de-los-cidos-carboxlicos16204463
Glossary
Acyl group: carbonyl group connected to an alkyl group (Bruice, 2007).
Alcohol: Compound that has an OH as functional group.
Carboxylic acid: compound that has a COOH as functional group.
Ester: compound in which an H of a carboxylic acid has been substituted by a hydrocarbon
group (Brown et al., 2004).
Halogen: chemical element found in group VII A of the periodic table.
Nucleophile: anion or neutral molecule that gives free electrons to another, forming a
covalent bond.
Nucleophilic substitution: a nucleophilic attack to the carbon that contains the group that
is going to be liberated.
Oxidation: chemical reaction in which an element transfers electrons to another element.
Strong acids: acids that are almost completely dissociated in aqueous solutions.
Vinegar: acetic acid dissolved to 0,5%.
Weak acids: acids that are partially dissociated in aqueous solutions.
Vocabulary box
Bridge (noun): a structure that is built over a river, road, or railway to allow people and
vehicles to cross from one side to the other.
Chemical bond (noun): an electrical force that holds atoms together to form a molecule.
Dimer (noun): a compound formed by the union of two radicals or two molecules of a
simpler compound.
Join (verb): to connect or fasten things together.
Dissociation (noun): the process by which a chemical combination breaks up into simpler
constituents.
Main (adjective): larger, more important, or having more influence than others of the same
type.
Catalyst (noun): something that makes a chemical reaction happen more quickly without
itself being charged.
Protonate (transitive verb): to add a proton to.
Sources:
http://dictionary.cambridge.org
http://www.merriam-webster.com
English review topic

Relative clauses (which, that)