The stoichiometry of the additions is 1:1, meaning that for every one mole of tr

Question

The stoichiometry of the additions is 1:1, meaning that for every one mole of trons-cinnamic add. one mole of Br_2 is needed to form the addition product. The Br_2 presents at a solution in dichloromethane solvent. This often causes problems for students when calculating stiochiometric equivalents. The bromine solution is 10% Br_2 by volume. For instance, 100 ml of solution contain 10 ml of Iiquid Br_2. The density of Br_2 is 3.12 g/mL. Calculate the number of mmol of Br_2 present in 0.48 ml of bromine solution Calculate the number of mmol in 100. mg of trons-cinnamic acid (use a MW calculated to 2 decimal places] Which is the limiting reagent? What is the theoretical yield of the addition product? (use a MW calculated to 2 decimal places) Show all calculations. Your TA and I want to see a prediction work out the probable stereochemistry of the product as part of the mechanism in your preparatory write-up. " " Remember what a fischer projection implies about the stereochemistry at each center. Models help tremendously here. Come prepared to discuss and defend your work during the pre-lab discussion

Explanation / Answer

Molar mass of Trans cinnamic acid is 148.1586 g/mol

Moles of cinnamic acid = 100 mg / molar mass in mg per mol

=100 mg x 1 mmol / 148158.6 mg = 0.674952382        mmol          

Molar mass of Br2 is 159.808 g/mol

Volume of Br2 solution is 0.48 mL

Volume percent of Br2 is 10 so we find the volume of Br2 in in its solution is

=0.48 x 10/100= 0.048 mL          

Mass of Br2 = volume x density

= 0.048 mL x 3.12 g/mL = 0.14976 g

Moles of Br2 = 0.14976 g x 1 mol / 307.966 g

= 0.000937125 mmol = 0.937124549 mmol Br2

Determination of limiting reactant.                                                                

limiting reactant                                                                                

mol ratio is 1:1 so both moles should be equal. We can see that cinnamic acid has lower moles than Br2 so it cinnamic acid is the limiting reactant.

Formation of product

=m mols of limiting reactant (cinnamic acid ) x 1 mmol product / 1 mol cinnamic acid

= 0.674952382 mmol cinnamic acid x 1 mol product / 1 mol cinnamic acid

=0.674952382 mmol product

Molar mass of product is 307.9666 g/mol

Mass of product formed

= mmol x molar mass in mg/mol

=0.674952382 mmol x 105.808 mg/mmol                           

=207.8627903 mg   

Theoretical yield is 207.86 mg

                            

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