Question

in this lab you are synthesizing acetylsalicylic acid (asa) from salicylic acid using acetic anhydride, with phosphoric acid as a catalyst.
if the amount of salicylic acid at the start of the reaction was 1.05 g, what is the theoretical yield of asa in g? assume acetic anhydride is in excess.
hint: the structures of all the compounds you need are in the lab manual.
answer:

Explanation:

Step1: Calculate the molar mass of salicylic acid

The molar mass of salicylic acid ($C_7H_6O_3$) is $M_{salicylic\ acid}=(7\times12)+(6\times1)+(3\times16)=138\ g/mol$.

Step2: Calculate the number of moles of salicylic acid

Using the formula $n = \frac{m}{M}$, where $m = 1.05\ g$ and $M = 138\ g/mol$. So $n_{salicylic\ acid}=\frac{1.05}{138}\ mol$.

Step3: Determine the mole ratio between salicylic acid and ASA

From the reaction equation (not shown here but based on the synthesis reaction), the mole ratio of salicylic acid to ASA ($C_9H_8O_4$) is $1:1$.

Step4: Calculate the molar mass of ASA

The molar mass of ASA is $M_{ASA}=(9\times12)+(8\times1)+(4\times16)=180\ g/mol$.

Step5: Calculate the theoretical yield of ASA

Since $n_{ASA}=n_{salicylic\ acid}$, and $m = n\times M$. So $m_{ASA}=\frac{1.05}{138}\times180\ g$.

$$m_{ASA}=\frac{1.05\times180}{138}\approx1.37\ g$$

Answer:

$1.37$