Calculate the mass of zinc you will use. One equivalent of zinc is the mass need

Question

Calculate the mass of zinc you will use. One equivalent of zinc is the mass needed to react with the amount of stilbene dibromide used. Give your answer in grams and show your working below.

Reaction = C14H14Br2 + Zn ----> C14H12 + ZnBr2

Method= In this procedure, you will recycle the stilbene dibromide that you made last week. The solvent and reagent are non-toxic and the procedure is neither time nor energy intensive. Note that the by-product, zinc bromide, can cause burns.

1. Into a 100 mL round bottom flask place 0.5 g stilbene dibromide, 10 mL ethanol and a stir bar. 2. Add 1.25 equivalents (i.e. 1.25 fold excess) of zinc powder

3. Reflux and stir the reaction using a hot water bath (at 90-1000 C) as described in Padias.

4. When all the solid has dissolved (after 30-60 minutes or so), preheat a fluted filter paper and filter funnel with 3 mL boiling ethanol in a 50 mL Erlenmeyer flask on a hot plate.

5. Remove the reflux condenser. Using the clamp as a handle for the hot round bottom flask, filter the reaction mixture while keeping the solution and filter paper hot.

6. Allow the filtrate to cool to room temperature. Crystals should start to form

7. Cool the flask in ice to bring down more crystals

8. Collect the crystals by vacuum filtration. Rinse with a small volume of ice-cold ethanol. Continue to draw air through the crystals to dry them.

9. Record the yield.

10. Record the melting point of your product (which should be above 1000 C) and a mixed melting point with stilbene

11. Compare your product with stilbene and stilbene dibromide by TLC.

Explanation / Answer

you have used 0.5 gram stillben bromide

moles of stillbin bromide = weight / molar mass

= 0.5 / 337.93

= 0.00148 moles

actually you added 1.2 equilent of Zn so

= 0.00148 x 1.2

= 0.001776 moles of Zn poweder required

no weight of Zn = moles of Zn x molar mass of Zn

= 0.001776 x 65.4

= 0.1162 grams zinc required

remember i calculated fro 1.2 equilent zinc not for one equilent because in procedure you added 1.2 equilent

but question you asked 1 equilent

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