Video Transcript
Fill in the blank. The addition of sulfuric acid to ethene, followed by dilution with water and distillation, can be used to produce blank. (A) Ethylene glycol, (B) ethane, (C) ethanal, (D) ethanol, or (E) ethanoic acid.
The question tells us that sulfuric acid is added to ethene. The prefix eth- tells us that ethene contains two carbon atoms. The suffix -ene tells us that ethene is an alkene and contains a carbon-carbon double bond. We can use this information to draw the structure of ethene.
Alkenes like ethene undergo addition reactions with a variety of substances because the carbon-carbon double bond is so reactive. When the double bond of ethene reacts with sulfuric acid, the 𝜋 bond of the alkene is broken, as is the bond between a hydrogen atom and an oxygen atom in a molecule of sulfuric acid. Two new bonds are formed: one between a carbon atom that was a part of the alkene and the hydrogen atom from the sulfuric acid and the other between the rest of the sulfuric acid molecule and the other carbon atom that was a part of the alkene. As ethene is symmetrical, it doesn’t matter which carbon atom the hydrogen adds to. The product will be the same.
At this point in the experiment, we have produced ethyl hydrogen sulfate. The question tells us that this reaction is followed by dilution with water. When water and ethyl hydrogen sulfate are mixed, the hydroxy group from the water can replace the hydrogen sulfate. This produces a product that contains a hydroxy group along with sulfuric acid. This reaction is a hydration reaction, a chemical reaction where water is added to a compound. The entire process shown is known as indirect hydration, as water is not added in a single step.
So, in essence, the question is asking us to determine the product of the indirect hydration of ethene. Let’s take a closer look at the product and the answer choices. The product contains two carbon atoms. When naming organic compounds, we use the prefix eth- to indicate two carbon atoms. Looking at the answer choices, we see that each contains the prefix eth-. So we can’t yet eliminate any of the answer choices.
The carbon atoms of the product are joined by a single covalent bond. When naming organic compounds, we can use the term “ane,” often shortened to A-N, to indicate that there are only single covalent bonds between the carbon atoms. We see that answer choices (B) through (E) all contain this term. We might be tempted to eliminate answer choice (A) as the A-N or “ane” term does not exist in the name. However, ethylene glycol is the common name of ethane-1,2-diol, which does contain the term “ane.” So we still can’t eliminate any of the answer choices.
The product contains a hydroxy group. This is the primary functional group for a class of molecules known as alcohols. When naming organic compounds, we use the suffix O-L to indicate that the molecule is an alcohol. Looking at the answer choices, we can see that answer choice (A) and (D) contain the O-L suffix. Answer choice (B) does not contain an additional functional group suffix. Answer choice (C) has the suffix A-L. This indicates that the primary functional group of this molecule is an aldehyde, not an alcohol. Answer choice (E) ends in -oic acid. This indicates that the primary functional group of this molecule is a carboxylic acid, not an alcohol. From this information, we can eliminate answer choices (B), (C), and (E).
Looking at answer choice (A), we see the term di- in front of the ending -ol. This indicates that the molecule contains two hydroxy groups. But the product we drew only contains one hydroxy group. So we can eliminate answer choice (A). This means that the addition of sulfuric acid to ethene followed by dilution with water and distillation can be used to produce ethanol, answer choice (D).
