The portal has been deactivated. Please contact your portal admin.

Question Video: Determining the Products of the Cracking of Decane Chemistry • 7th Grade

Decane is a relatively large saturated hydrocarbon that can be broken down into smaller molecules during a cracking reaction. Which of the following pairs of molecules could be produced when a single molecule of decane is broken down during a cracking reaction? [A] C₈H₁₈ + C₂H₄ [B] C₈H₁₈ + C₂H₆ [C] C₈H₁₆ + C₈H₁₄ [D] C₂H₄ + C₉H₂₀ [E] C₂H₄ + C₁₀H₂₂

03:50

Video Transcript

Decane is a relatively large, saturated hydrocarbon that can be broken down into smaller molecules during a cracking reaction. Which of the following pairs of molecules could be produced when a single molecule of decane is broken down during a cracking reaction? (A) C8H18 plus C2H4. (B) C8H18 plus C2H6. (C) C8H16 plus C8H14. (D) C2H4 plus C9H20. Or (E) C2H4 plus C10H22.

To answer this question, we need to know how many carbon atoms are in a molecule of decane. From the -ane portion of its name, we know that decane is an alkane, and its prefix dec- indicates that it contains 10 carbon atoms. When decane undergoes cracking, it is broken down into smaller molecules. After the cracking process, the total number of carbon atoms in the two product molecules will be the same as the total number of carbon atoms in the large decane molecule.

As decane has 10 carbon atoms, the total carbon atoms for the two smaller molecules should also be 10. With this in mind, we can have a look at the answer choices.

For answer choice (A), the total number of carbon atoms is eight plus two, which gives us 10 and is the same for answer choice (B). Answer choice (C) is eight plus eight, which gives us a total of 16 carbon atoms, 11 carbon atoms for answer choice (D), and 12 carbon atoms for answer choice (E). Since the products in answer choices (C), (D), and (E) do not have a total of 10 carbon atoms, we can eliminate them.

To determine the chemical formulas for the two product molecules, we must consider the type of hydrocarbon that decane is. The question tells us that decane is a saturated hydrocarbon, which means that in its structure the carbon atoms engage in only single bonds with each other. During the cracking reaction of a saturated hydrocarbon, smaller alkanes and alkenes are produced. The general formula for an alkane is C𝑛H2𝑛+2, where 𝑛 is a whole number representing the number of carbon atoms in the structure. We can see that the first product listed in both answer choices (A) and (B), C8H18, fits this general formula and thus is our alkane product.

Therefore, the second product must be an alkene and must fit the general formula for alkenes, which is C𝑛H2𝑛, where 𝑛 again is a whole number representing the number of carbon atoms in the structure. We can see that the second product in answer choice (B) does not fit the general formula for an alkene. We can eliminate answer choice (B). The second product listed in answer choice (A) does fit this general formula and is thus an alkene.

Therefore, the pair of molecules that could be produced when a single molecule of decane is broken down during a cracking reaction is answer choice (A) C8H18 plus C2H4.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.