Chemistry Question

Using robust details and ample evidence, create a reflection essay that describes 4 learning objectives you met while performing this experiment.  View the learning objectives from the lab manual provided and select four to focus your writing on.

Virtual Lab Manual
Organic Chemistry Introduction:
Learn about organic compounds
Synopsis
What do all living things, and even some non-living things, have in common? They are all built
from organic compounds! In the Organic Chemistry Introduction simulation, you will learn
what an organic compound is. With your lab assistant Dr. One, you explore how organic
compounds are structured, how we name them, and how we represent them in both 2D and
3D.
Test the functional groups
A central concept in Organic Chemistry is functional groups. You will use your acquired
knowledge to help your friend, Simon, by determining if a medicine he has received can be
trusted. Guided by Dr. One, you will carry out basic chemical tests to verify the functional
groups this medicine contains, and learn about some of the ways organic compounds can
react.
Make it react
The lab focuses on a high level of interactivity. When working with types of carbon bonds and
their angles, you get to build your own 3D carbon molecules on our holotable. In the fume
hood, you can make mistakes with the hazardous solutions without consequences, and
become comfortable with the equipment we use. Quiz questions on-the-go ensure that you
learn the essential points. You can also always look at the Theory pages to extend your
knowledge further.
Solving the solutions
At the end of the Organic Chemistry Introduction simulation, you will have to combine the
test results and your knowledge to solve the organic chemistry puzzle.
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Will you be able to identify the right functional groups in Simon’s medicine and make sure he
will be okay when taking it?
Learning Objectives
At the end of this simulation, you will be able to…
● Give examples of uses of organic compounds
● Identify the carbon valence electrons and the hybridization of their orbitals
● Predict the angles of covalent bonds of carbon atoms in hydrocarbons
● Apply the nomenclature of simple hydrocarbons
● Interpret some of the important representations of hydrocarbons
● Give examples of functional groups of organic compounds and their reactions
Techniques in Lab
●
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Bromine test for unsaturated hydrocarbons
Ceric Ammonium Nitrate test for alcohols and phenols
Theory
The nature of organic compounds
Organic chemistry is the study of organic compounds and their structure, properties, and
reactions. Organic compounds are chemicals that are based on the element carbon, and
most often they would also contain bonds between carbon and hydrogen. Methane, a
hydrocarbon, shown in Figure 1, is one of the simplest organic compounds.
Figure 1: Structure of methane, a simple organic compound.
Many organic compounds contain elements other than carbon and hydrogen, typically
oxygen and nitrogen, but it can also be other groups such as phosphorus or halogens.
Some carbon compounds are not considered to be organic, e.g., carbonates and carbon
oxides like carbon monoxide and carbon dioxide. These types of compounds are regarded as
inorganic.
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Hydrocarbons
Hydrocarbons are a subgroup of organic compounds, which contain only carbon and
hydrogen. Examples of hydrocarbons can be seen in Figure 2.1. Salicylic acid, shown in Figure
2.2, is an organic compound, but it’s not a hydrocarbon as it contains oxygen groups.
Figure 2.1: Structure of the hydrocarbons methane, propane, and 1-butene.
Figure 2.2: Structure of the hydrocarbons methane, propane, and 1-butene.
Electrons of carbon
A carbon atom has 6 electrons, arranged in the configuration 1s² 2s ² 2p ². The 2 electrons in
the 1s orbital are not of interest in organic chemistry, as they do not partake in the reactions
involved here. The remaining four electrons are the carbon atoms valence electrons, as these
are available for forming covalent bonds. From the electron configuration, you would expect
carbon to only form two bonds, but due to orbital hybridization, carbon can meet the octet
rule of having eight electrons in its outer shell.
The octet rule
The octet rule states that atoms combine to obtain eight electrons in their outer shell.
Hydrogen atoms, which often seek to have 2 electrons in their outer shell, are a notable
exception.
Orbital hybridization
Orbital hybridization is the mixing of the outer shell orbitals in an atom in order for it to be
able to complete the octet rule. For carbon, this means that the electrons in the 2s, 2pₓ, and
2pᵧ combine to form new, equivalent orbitals. If the carbon atom only forms single bonds, sp³
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hybridization produces four equal orbitals. If a double bond is formed, sp² hybridization
produces three equal orbitals, with a single 2p orbital left to form the second part of the
double bond. If a triple bond is formed, sp hybridization produces 2 equal orbitals, with two
2p orbitals left to form the second and third part of the double bonds.
When carbon forms bonds with hybridized orbitals, the bond is a σ (sigma) bond. The bonds
formed with unhybridized orbitals for the remaining part of double or triple bonds are called
π (pi) bonds.
Carbon bond angles in organic compounds
The angles between the bonds in organic compounds depend on the hybridization and
therefore the types of bonds formed by each of the carbon atoms. If only single bonds are
present, the angle between each of these is 109.5°. If a double bond is formed, the angle
between the bonds is 120°, and if a triple bond is involved, the angle is 180°. See Figure 3 for
examples of the angles described above. The angles of the bonds have important
implications for which products are formed in chemical reactions involving organic
compounds.
Figure 3: Organic compounds showing how the angles of the compound depend on the bonds
it forms.
Nomenclature of simple hydrocarbons
Simple hydrocarbons are named based on a few straightforward rules. The first part of the
name – the prefix – is determined by the number of carbon atoms in the longest carbon
chain. The second part of the name – the suffix – is determined by whether double or triple
bonds are present. A visual representation of these principles can be seen in Figure 4.
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Figure 4: Overview of the nomenclature principles of simple hydrocarbons.
If more than one location is possible for a double or triple bond, a number is added to
indicate its placement on the carbon chain, always counting from one end of the chain and
giving the carbon the lowest number possible.
Hydrocarbon prefixes
Prefixes for simple hydrocarbons are determined by the number of carbon atoms in the
longest carbon chain. Figure 5 shows the general principle of assigning prefixes regardless of
the type of bonds involved in the compound.
Figure 5: Role of the prefixes in names of hydrocarbons.
List of hydrocarbon prefixes
The following table shows the prefixes for hydrocarbons with 1-10 carbon atoms present in
the longest carbon chain. Note that only the prefix is shown in the second column and that
the whole name includes the suffix, which for hydrocarbons depend on whether double or
triple bonds are present in the compound.
Table 1. List of prefixes in names of hydrocarbons and examples of complete names.
NUMBER OF CARBON ATOMS
PREFIX
COMPOUND EXAMPLE
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1
2
3
4
5
6
7
8
9
10
MethEthPropButPentHexHeptOctNonDec-
Methane
Ethene
Propyne
1-Butene
Pentane
3-Hexyne
2-Heptene
Octane
1-Nonyne
4-Decene
Hydrocarbon suffixes
Suffixes for simple hydrocarbons are determined by the type of bonds present. See Figure 6
which suffixes apply.
Figure 6: Overview of hydrocarbon suffixes.
Hydrocarbon side groups
Side groups of only carbon and hydrogen in organic compounds have the same prefixes as
the hydrocarbons. The suffix used is -yl.
If there are side groups on the longest chain of carbon atoms, these are numbered by the
carbon they are attached to. The carbon number for this group of organic compounds is
assigned so:
1) You always count from one end of the longest carbon chain with the most important
functional group
2) If a double or triple bond is present, this should get the lowest number possible
3) If only single bonds are present, the side groups should get the lowest number possible
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If a side group can only be positioned in one place in the compound, the number can be
omitted.
Check out the examples from the simulation in Figure 7 to see how the numbers are
assigned
Figure 7: More examples of hydrocarbons with side groups.
Saturated vs. unsaturated hydrocarbons
A hydrocarbon is saturated if it contains no double or triple bonds. If either of these is
present in a compound, this will make it unsaturated. Figure 8 shows a visual representation
of this principle.
Figure 8: Overview of saturated vs. unsaturated compounds.
The molecular formula of a non-cyclic alkane will follow this rule for the number of carbons
and hydrogens: CnH₂n+₂.
Non-cyclic alkenes follow this rule: CnH₂n.
Non-cyclic alkynes follow this rule: CnH₂n-₂.
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Structural isomerism
Structural isomers are compounds that share the same molecular formula but have different
arrangements of the atoms. There are several subgroups of structural isomerism. In chain
isomers the carbon backbone of the compound is rearranged, but still contains the same
number of carbon and hydrogen atoms.
Figure 9: Examples of pairs of chain isomers. The first two compounds both have the formula
C4H10, the last two compounds both have the formula C6H14.
Another type of structural isomers are position isomers, which are based on the position of
functional groups in the molecule. This position slightly alters the name of the molecule to
indicate where the functional group is located, and it can have a huge influence on the
reactions the molecule takes part in. 1-Butene and 2-butene are position isomers as the
double bond is positioned differently in otherwise identical compounds.
Branched hydrocarbons are sometimes named based on the prefix they would be assigned if
all carbons were in a single chain. E.g., methyl-propane, which has four carbons, often also
go by the name isobutane, where iso- denotes that it’s a structural isomer of butane, which
can only be methyl-propane.
Skeletal formulas
Skeletal formulas are a simplified way of representing organic compounds. Instead of writing
out all the carbon and hydrogen atoms, they are implied by corners, also called ‘vertices’, in
the structure. See for example Figure 10.1. Only carbon and hydrogen can be omitted this way.
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Figure 10.1: The organic molecule benzene with all atoms drawn out (left), and the simplified
skeletal structure (right), which is commonly used.
Skeletal structures are a great way to more clearly show important aspects like functional
groups of an organic compound, see Figure 10.2 for the skeletal structure of salicylic acid. A
combination of the two ways of drawing the structure can be used as well.
Figure 10.2: The skeletal structure of salicylic acid with molecular formula C₇H₆O₃.
Functional groups
Functional groups are the parts of a molecule responsible for its reactivity. Different
functional groups give rise to different reaction types in organic chemistry.
Functional groups can be a specific arrangement of carbon and hydrogen, e.g. a double bond,
or can also include other elements. The most common elements in organic compounds
besides carbon and hydrogen are oxygen and nitrogen. Other examples of elements are
phosphorus and halogens. You can see the functional groups of salicylic acid in Figure 11.
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Figure 11: The functional groups of salicylic acid. Purple = phenol; green = carboxylic acid;
blue = phenyl.
Positive and negative controls
In chemistry, controls are a way to validate the results of your experiment. A positive control
should show a positive result in a test, whereas a negative control should show a negative
result. If the result is not as expected, you cannot trust that the test was performed
correctly for your actual experiment.
Ceric ammonium nitrate test
The ceric ammonium nitrate test is a way to examine a solution for the presence of either
alcohols or phenols. In solution, the orange-yellow ceric ammonium nitrate makes a complex
with the alcohol or phenol, which results in a color change in the solution. Alcohols cause a
red color change, whereas phenols induce a more dark-red to dark-brown color change,
depending on the phenol involved.
The reaction is as follows:
Materials
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Test tubes
Test tube rack
Ceric ammonium nitrate solution
Compound to be tested
Safety information
Ceric ammonium nitrate is a strong oxidizer, corrosive, an irritant, and an environmental
hazard. Contact with other materials may cause a fire. It is harmful if swallowed and eye
contact may result in permanent eye damage. It causes eye, skin, and respiratory tract
irritation.
Procedure
⮚
Make a solution of the organic compound dissolved in a suitable solvent. Put 1 mL in a
test tube.
⮚
Add a few drops of ceric ammonium nitrate solution.
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⮚
If the solution becomes a red color, then an alcohol group is present in the organic
compound.
⮚
The red color disappears if:
o
o
You keep the reaction mixture for some time.
You add an excess of ceric ammonium nitrate solution. Therefore, avoid using
an excess of ceric ammonium nitrate solution.
Sodium bicarbonate test
Sodium hydrogen carbonate, also known as sodium bicarbonate, reacts with acidic solutions
to form carbon dioxide, which is released as gas from the solution, resulting in so-called
brisk effervescence. Sodium hydrogen carbonate can be used to test for carboxylic acids. If
effervescence occurs, then an acid group is present.
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The reaction is as follows:
Phenol is a weak acid meaning it dissolves in sodium hydroxide solution but does not
dissolve in sodium hydrogen carbonate solution. Stronger acids, such as carboxylic acids,
dissolve in both solutions. This can be useful for separating mixtures of acids.
Materials
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Test tubes
Test tube rack
Sodium hydrogen carbonate solution
Compound to be tested
Safety
Acidic solutions are corrosive. Sodium hydrogen carbonate is an irritant.
Procedure
1. Put 2 mL of a saturated aqueous solution of sodium hydrogen carbonate in a clean
test tube.
2. Add a few drops of the liquid compound or a few crystals of the solid compound to it.
Add the compound slowly so that effervescence is clearly visible.
3. Brisk effervescence of carbon dioxide indicates the presence of a carboxylic acid
group.
Bromine test
The bromine test is used to test for an unsaturated carbon carbon bond, such as an alkene
or alkyne. The test uses a type of chemical reaction called addition, where a reactant, here
bromine, is added to an organic compound to break a double or triple bond.
For example, the addition of bromine to but-2-ene:
Bromine has an orange-brownish color when in solution, so the color of the solution is lost
when an alkene or alkyne is present for bromine to react with. Bromine will also react with
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aromatic compounds, such as phenol, but it can’t react with alkanes as they contain only
single bonds, and therefore there is no color change when these are mixed. Benzene can
react with bromine in the presence of a catalyst, but not without a catalyst since it is not
reactive enough. Phenol is more reactive than benzene so can react with bromine without a
catalyst. This is because the alcohol group donates electron density into the delocalized
benzene ring.
Materials
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Test tubes
Test tube rack
Carbon tetrachloride
Chloroform
Bromine water
Compound to be tested
Safety information
Bromine is corrosive, toxic, and an environmental hazard. Bromine causes eye and skin burns,
as well as digestive and respiratory tract burns. It may be fatal if inhaled and is a strong
oxidizer. Contact with other material may cause a fire. Corrosive to metal. Carbon
tetrachloride is toxic. Chloroform is harmful. This test should be performed at room
temperature.
Procedure
1. Dissolve 0.1 g or 5 drops of organic compound in 2 mL of carbon tetrachloride. If you
do not have carbon tetrachloride, a solvent such as chloroform or water can be used
to dissolve the organic compound.
2. Add 2% solution of bromine water drop by drop with continuous shaking.
3. If the bromine solution becomes colorless then there is an unsaturated carbon carbon
bond in the organic compound. This test should be confirmed with the Baeyer’s test.
Hydrocarbons in water
Hydrocarbons are nonpolar, which means that they generally don’t mix well with water.
Simple hydrocarbons that are liquid at room temperature, such as hexane, have a lower
density than water, and therefore form a separate layer on top of water. These layers are
called phases. This two-phase system can be used for e.g., extracting organic compounds
from a water sample into hexane, which can have many advantages in analytical chemistry.
Alcohols and phenols
In organic chemistry, alcohols are a functional group where a hydroxy (-OH) group is bound to
a saturated carbon. If the hydroxy group is bound to an aromatic ring, the functional group is
called a phenol. See examples of an alcohol and phenol in Figure 1. Note that phenol is both
the name of the functional group, and the simplest compound within this group.
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Figure 12: Structures of ethanol and phenol.
Aromatic rings
Aromatic rings are a common group in organic chemistry. They are planar ring systems, where
a series of double bonds make the molecule conjugated, which means that the p orbitals
used for the π bonds overlap with p orbitals on both sides of each carbon atom. Figure 16
shows benzene, one of the simplest aromatic compounds. Though commonly drawn like this,
each carbon in the compound is actually bonded in the exact same way to both of its
neighbors.
Figure 13: The structure of benzene, one of the simplest aromatic compounds.
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