Question

If there are 0.064g of theobromine in a 43g chocolate bar, how many moles of theobromine are there?

Answer 1

Answer: $3.5\times 10^{-4}$

Explanation:

To calculate the moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text {Molar mass}}$

Given mass of theobromine $(C_7H_8N_4O_2)$ = 0.064 g

Molar mass of theobromine $(C_7H_8N_4O_2)=12\times 7+1\times 8+14\times 4+16\times 2=180 g$

$\text{Number of moles}=\frac{0.064g}{180g/mol}=3.5\times 10^{-4}moles$

Answer 2

If the problem is finding the moles of theobromine, then the 43 g chocolate is not really a necessary information. All you have to do is convert 0.064 g of theobromine to moles using molar mass. The molar mass of theobromine is 180.164 g/mol. So,

0.064 g (1 mol / 180.164 g) = 3.6 x10^-4 moles

The answer would be letter A or the first choice :)