Question

the compound dopamine contains 62.72% c, 7.24% h, 20.89% o, and 9.15% n by mass. what is the empirical formula for dopamine? (enter the elements in the order: c, h, n, o.) the empirical formula is . an error has been detected in your answer. check for typos, miscalculations etc. before submitting your answer. 2 item attempts remaining try another version submit answer

Explanation:

Step1: Assume 100g of dopamine

Since the percentages are by - mass, in 100g of dopamine, we have 62.72g of C, 7.24g of H, 20.89g of O, and 9.15g of N.

Step2: Calculate the number of moles of each element

The molar mass of C is 12.01g/mol, of H is 1.01g/mol, of O is 16.00g/mol, and of N is 14.01g/mol.
The number of moles of C: $n_C=\frac{62.72g}{12.01g/mol}\approx5.22mol$
The number of moles of H: $n_H=\frac{7.24g}{1.01g/mol}\approx7.17mol$
The number of moles of O: $n_O=\frac{20.89g}{16.00g/mol}\approx1.30mol$
The number of moles of N: $n_N=\frac{9.15g}{14.01g/mol}\approx0.65mol$

Step3: Divide by the smallest number of moles

The smallest number of moles is 0.65mol.
For C: $\frac{5.22mol}{0.65mol}\approx8$
For H: $\frac{7.17mol}{0.65mol}\approx11$
For O: $\frac{1.30mol}{0.65mol}=2$
For N: $\frac{0.65mol}{0.65mol}=1$

Answer:

$C_8H_{11}NO_2$