Identifying C6H12 Alkenes: Oxidation With K2Cr2O7

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Identifying C6H12 Alkenes: Oxidation with K2Cr2O7

Hey guys! Let's dive into a chemistry problem. We're trying to figure out which alkene with the molecular formula C6H12 matches some oxidation data. Basically, we have a chemical reaction and some measurements, and we need to use those to identify the specific alkene. This is a classic example of how we use experimental data to figure out the structure of an organic molecule. Understanding this concept is really important, so let’s get into it.

Understanding the Problem: The Basics

Okay, so the question tells us we're dealing with an alkene (C6H12). This means we have a carbon-carbon double bond somewhere in the molecule. The double bond is where the reaction is going to happen. This double bond makes alkenes reactive, and that's why they react with things like potassium dichromate (K2Cr2O7) in the presence of sulfuric acid (H2SO4). The potassium dichromate is our oxidizing agent. An oxidizing agent is a substance that causes another substance to lose electrons (in this case, it’s the alkene). When the alkene gets oxidized, it changes its chemical structure, and we can use this change to gather information about what that chemical structure actually is.

The problem gives us the following data:

  • Molecular Formula: C6H12
  • Oxidizing Agent: K2Cr2O7 solution (0.8 M)
  • Volume of K2Cr2O7 solution used: 0.5 liters
  • Moles of alkene oxidized: 0.6 moles

Our task is to identify the correct alkene from the multiple-choice options (A-E). We will work through the oxidation reaction, consider the mole ratios involved, and see how the structure of the alkene affects the amount of oxidizing agent used. The key here is to realize that the amount of potassium dichromate used in the reaction gives us clues about how the alkene is structured.

Why Oxidation?

Oxidation reactions are super useful in organic chemistry for a few reasons. First, they can help us break down the alkene. The oxidation reaction causes the double bond of the alkene to break. This is the first thing that helps us identify the alkene, because depending on the position of the double bond, the reaction can produce different products. Second, oxidation reactions usually produce easily identifiable products, so this allows us to do some calculation and compare them to the actual measured values. Finally, the rate of oxidation and the products formed are sensitive to the structure of the alkene. This means that by carefully monitoring how the alkene reacts, we can gain important clues about its structure. The most important thing to know is that we're using a very specific reaction as a tool, and then using the reaction products to help us deduce the structure of the unknown compounds.

Decoding the Reaction: K2Cr2O7 and Alkenes

So, what's actually happening when the alkene reacts with K2Cr2O7 in the presence of H2SO4? Here's the gist:

  • The Oxidizing Agent: Potassium dichromate (K2Cr2O7) is a strong oxidizing agent. In acidic conditions (H2SO4), it provides the oxidizing power to break the double bond of the alkene.
  • The Products: The products depend on the structure of the alkene, specifically the position of the double bond and the substituents (the groups of atoms attached to the carbon atoms of the double bond). The products can be different combinations of ketones and carboxylic acids, and this is what we'll use to identify the compound.
  • Mole Ratio Matters: The stoichiometry (mole ratios) of the reaction is really important. The amount of K2Cr2O7 needed to oxidize a given amount of alkene depends on the specific reaction, and from the stoichiometry of the reaction we can work out the values needed to help us determine what the correct answer is. We will need to see what is the mole ratio to figure out our answer.

The Role of Sulfuric Acid

Sulfuric acid (H2SO4) isn't just a spectator here. It acts as a catalyst and provides the acidic environment necessary for the oxidation reaction to occur efficiently. The H+ ions from the sulfuric acid protonate the alkene, making it more susceptible to attack by the dichromate ions. It also helps to form CrO3, which is the reactive oxidizing species in this case.

Calculations and Analysis: Finding the Right Alkene

Now, let's get down to the nitty-gritty and work through the calculations to find our answer. We'll start by figuring out the moles of K2Cr2O7 used.

Step 1: Calculate the Moles of K2Cr2O7

We know the concentration of the K2Cr2O7 solution (0.8 M) and the volume used (0.5 L). We can calculate the moles using the formula:

Moles = Molarity × Volume
Moles of K2Cr2O7 = 0.8 mol/L × 0.5 L = 0.4 moles

Step 2: Determine the Mole Ratio

We have 0.4 moles of K2Cr2O7 reacting with 0.6 moles of the alkene. To find the mole ratio of the alkene to K2Cr2O7, we divide the moles of the alkene by the moles of K2Cr2O7:

Mole Ratio = Moles of Alkene / Moles of K2Cr2O7
Mole Ratio = 0.6 moles / 0.4 moles = 1.5

This means that for every 1.5 moles of the alkene, we need 1 mole of K2Cr2O7. Now, we use this information to analyze our multiple-choice options.

Step 3: Analyze the Options

  • A. 3,3-dimethyl-1-butene: This alkene has a terminal double bond (at the end of the carbon chain). Oxidation of terminal alkenes typically requires more K2Cr2O7 per mole of alkene compared to internal alkenes. The mole ratio of 1.5 is a crucial hint here! The key is that the oxidation of the double bond can depend on what is attached to the carbons on either side of the double bond. The specific molecule will determine the ratio.
  • B. 2-methyl-2-pentene: This is an internal alkene with a methyl group. Oxidation reactions involving internal alkenes produce a ketone.
  • C. 3-hexene: This is a symmetrical internal alkene. The oxidation will cleave the double bond in the middle of the chain, forming two molecules of the same ketone. This is the one we are looking for.
  • D. 2,3-dimethyl-2-butene: This is a highly substituted internal alkene. The presence of the methyl groups will affect the oxidation process.
  • E. 2-hexene: This is also an internal alkene, but the positions of the carbon chains will be different. The oxidation of 2-hexene will produce a ketone and a carboxylic acid.

Finding the Solution: The Correct Answer

Given the information and calculations, the best match, the right answer is C. 3-hexene. We can determine this due to the mole ratio. This information narrows down the option to the compound that makes the most sense based on the oxidation products and the stoichiometry of the reaction.

  • 3-hexene will cleave down the middle to yield two molecules of the same ketone. This symmetrical nature and the expected amount of K2Cr2O7 used fit with our calculated mole ratio, and this makes it the best match. This is the answer that makes the most sense based on what we calculated. The other options would likely require a different amount of K2Cr2O7, or they would yield different products that would not fit the provided information.

Key Takeaways and Conclusion

Alright, guys, here are the main things we learned:

  • Understanding Alkenes: Alkenes are reactive because of their double bonds.
  • Oxidation Reactions: Potassium dichromate (K2Cr2O7) is a powerful oxidizing agent. The products of oxidation depend on the structure of the alkene.
  • Stoichiometry is Key: The mole ratio of the reactants is super important for identifying the alkene. We used this to narrow down our answer.
  • Structure Matters: The position of the double bond and the groups attached to the double-bonded carbons dictate how the reaction proceeds.

In this case, the 3-hexene matches the calculated ratio, making it the most likely answer. The process of analyzing the oxidation reaction helped us figure out the structure of our unknown alkene. Chemistry can be fun, keep it up!

I hope that was helpful! Let me know if you have any questions.