Use the following atomic weights and quantities to calculate the overall % yield

Question

Use the following atomic weights and quantities to calculate the overall % yield of benzoin. Remember that your yield must be based on the limiting reagent, and that grams must be converted to moles. For problems not involving a one to one stoichiometry it may be easier to calculate the theoretical yield in grams to calculate the % yield. Filling out most of the chart will help. Give only two significant digits in your answer. If after rounding the answer is a whole number, do not include a decimal point. C 12, H 1, CI 35.5, N- 14, Na- 23, O 16, S- 32 thiamine sodium + benzaldehyde benzoin hydrochloride hydroxide formula formula weight grams moles 2.737 5.579 1.450 theoretical yield (g) % yield Answer:

Explanation / Answer

ans)

1.

Formula of thiamine hydrochloride is C12H18Cl2N4OS. Calculate its formula weight as follows:

Formula weight of thiamine hydrochloride = 12 (wt. of C) + 18 (wt. of H) + 2 (wt. of Cl) + 4 (wt. of N) + 1 (wt. of O) + 1 (wt. of S)

Formula weight of thiamine hydrochloride = 12 (12) + 18 (1) + 2 (35.5) + 4 (14) + 1(16) + 1(32)

Formula weight of thiamine hydrochloride = 337

Given weight of thiamine hydrochloride is 4.771 g. Calculate moles of thiamine hydrochloride given as follows:

Moles of thiamine hydrochloride = wt. of thiamine hydrochloride / formula weight of thiamine hydrochloride.

Moles of thiamine hydrochloride = 4.771 g / 337 g

Moles of thiamine hydrochloride = 0.014

2.

Formula of sodium hydroxide is NaOH. Calculate its formula weight as follows:

Formula weight of NaOH = 1 (wt. of Na) + 1 (wt. of O) + 1 (wt. of H)

Formula weight of NaOH = 1 (23) + 1 (16) + 1 (1)

Formula weight of NaOH =40

Given weight of NaOH is 2.737 g. Calculate moles of NaOH given as follows:

Moles of NaOH = wt. of NaOH / formula weight of NaOH.

Moles of NaOH=2.737 g / 40 g

Moles of NaOH = 0.068

3.

Formula of benzaldehyde is C7H6O

Formula weight of benzaldehyde = 7 (wt. of C) + 6 (wt. of H) + 1 (wt. of O)

Formula weight of benzaldehyde = 7(12) + 6(1) + 1(16)

Formula weight of benzaldehyde = 106

Given weight of benzaldehyde is 5.579 g. Calculate moles of benzaldehyde given as follows:

Moles of benzaldehyde = wt. of benzaldehyde / formula weight of benzaldehyde.

Moles of benzaldehyde = 5.579 g / 106 g

Moles of benzaldehyde = 0.053

4.

Formula of benzoin is C14H12O2

Formula weight of benzoin = 14 (wt. of C) + 12 (wt. of H) + 2 (wt. of O)

Formula weight of benzoin = 14 (12) + 12 (1) + 2 (16)

Formula weight of benzoin = 212

In benzoin formation reaction two molecules of benzaldehyde reacts to form one molecule of benzoin. Thiamine hydrochloride and NaOH are required in catalytic amount. Thus yield will be calculated based on benzaldehyde as the limiting agent.

Calculate theoretical yield as follows:

Theoretical yield = [(1 mol of benzoin / 2 mol of benzaldehyde) x given moles of benzaldehyde] x formula weight per mole of benzoin

Theoretical yield = [(1/2 )x 0.053 ] x 212

Theoretical yield = 5.618 g

Practical yield is 1.450 g. Thus calculate percent yield as follows:

Percent yield = (Practical yield / Theoretical yield) x 100

Percent yield = 26 %

Therefore, overall yield of benzoin is 26 %.

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