A student passes 6.20 L of propene, measured at 298 K and 100 kPa, into a flask holding hydrogen…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student passes of propene, measured at and , into a flask holding hydrogen bromide and a little benzoyl peroxide. At that temperature and pressure one mole of gas occupies . The yield of 1-bromopropane is , and its molar mass is .
Find the moles of propene and the mass of 1-bromopropane that the student collects.
Need a reminder? The key ideaShow
An alkene adds HX by Markovnikov's rule: the more stable carbocation forms, so the halide goes to the carbon with more alkyl groups. A carbocation can rearrange to a more stable one by a hydride or methyl shift. With a peroxide, HBr adds by a radical chain to give the anti-Markovnikov product, because the more stable radical forms.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Moles of propene. .
Step 2. Moles of product. The yield is : .
Step 3. Mass. .
Answer: and . Without the peroxide the main product would have been 2-bromopropane, with the same molar mass.
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