n.) During the filtration process of this reaction, cold water and cold ethanol
ID: 997914 • Letter: N
Question
n.) During the filtration process of this reaction, cold water and cold ethanol are used to wash the product. Use the information provided in the table below in regard to water, ethanol, and organic molecules similar in size to ethanol to answer the following questions.
H H
/
H - C - C - H
/
H H
H H
/
H - C - C - OH
/
H H
H
H - C - C = O
/
H H
H
H - C - C = O
/
H OH
i.) Indicate which of the molecules in the chart above would be soluble in water. Justify your answer.
ii.) Explain the observed trends in boiling points in terms of intermolecular forces.
Compound Name Molecular Formula Structure Boiling Point () water H2O H-O-H 100.0 ethane C2H6H H
/
H - C - C - H
/
H H
-89 ethanol C2H5OHH H
/
H - C - C - OH
/
H H
78.4 ethanal C2H4OH
H - C - C = O
/
H H
20.2 ethanoic acid CH3COOHH
H - C - C = O
/
H OH
118Explanation / Answer
Ethane : MW: C2H6 = 12 X2 +6 X1 = 24+ 6 = 30 , Boiling Point = -89, Ethane is non polar unlike Ethanol does not have any polar -OH group to form the hydrogen bond with water , as a thumb rule as the branching increases the boiling point increases and decreases the solubility in water. Which also means as the branching increases the hydrophobicity increases which do not make them water soluble. For water solubility the substance needs to be polar to form hydrogen bonding with water whose energy should overcome the inter and intramolecular hydrogen bonding energies.
Ethanol has a -89 boiling point it also means that it exists in gaseous state and one requires sufficient cooling to bring it to the liquid state. Most of Gaseous compounds are not soluble in water.Here dispersion forces are quite strong, hydrogen bonds also render the molecule boiling point character. Since Ethane has weak hydrogen bonds and hence it has a negative boiling point.
Ethanol C2H5OH = 12 X2 +6 X1+16 =46 , Ethanol has a polar -OH , boiling point 78.4, polarity occurs due to difference in dipole moments of the atoms , here sufficent hydrogen bonding can occur with water molecules's hydrogens to form hydrogen bonds, secondly since the molecule is polar it is soluble in water and have a tendency to have substantial boiling point. Ethanol although contains carbon atoms , the hydrogen bond formation energies with water overcome the intra - and inter molecular attraction forces and hydrophobic forces and make it molecule water soluble. The intermolecular and intramolecular hydrogen bonding in ethanol raise its boiling point.
Ethanal (Acetaldehyde) C2H4O, MW: 12x2 +4 x1+16 = 24 +4+16 =44, Ethanal is polar in nature, the polarity occurs due to difference in dipole moments of the molecules. Although Ethanal contains 2 C atoms and 4 H atoms it has Electronegative oxygen that makes the molecule polar in nature and capable of forming hydrogen bonding with the water molecules. The hydrogen bond energies with the water molecules overcome the hydrophobic forces and inter and intra molecular hydrogen bonding within ethanal to make it water soluble as compared to ethane the molecule is polar in nature .Ethanal is organic and has C=O group giving it lowest boiling point. The inter and intra molecular hydrogen bond formation energies in ethanal are not strong enough and it has less boiling point.
Ethanoic Acid (Acetic Acid) CH3COOH , It has highest polarity in the group and thus forms the highest hydrogen bonding with the water molecule and most soluble in water. Since its an organic acid it tends to have more inter and intra moleculear hydrogen bonding and thus has highest boiling point the given group due to Two Oxygen (C=O and -OH group). The forces of attraction and hydrophobic forces within the molecules are overcome by hydrogen bonding with water to make it water soluble.
Water has boiling point of 100 due to highest inter and intramolecular hydrogen bodings.
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