Question

Salicylic acid, used in the synthesis of as- pirin, has mass composition 60.87% C, 4.38% H, and 34.75% O. What is the empirical for- mula of the compound?

Answer 1

Answer: Empirical formula is $C_2H_{2}O$

Explanation:

If percentage are given then we are taking total mass is 100 grams.

So, the mass of each element is equal to the percentage given.

Mass of C= 60.87 g

Mas of H = 4.38 g

Mass of O = 34.75 g

Step 1 : convert given masses into moles.

Mass of C =$\frac{\text{ given mass of C}}{\text{ molar mass of C}}= \frac{60.87g}{12g/mole}=5.07moles$

Moles of H =$\frac{\text{ given mass of N}}{\text{ molar mass of N}}= \frac{4.38g}{1g/mole}=4.38moles$

Moles of O=$\frac{\text{ given mass of O}}{\text{ molar mass of O}}= \frac{34.75g}{16g/mole}=2.17moles$

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For C = $\frac{5.07}{2.17}=2$

For H = $\frac{4.38}{2.17}=2$

For O =$\frac{2.17}{2.17}=1$

The ratio of C:H:O= 2 : 2: 1

Hence the empirical formula is $C_2H_{2}O$