Question

The source of bitterness in dark chocolate is the compound theobromine, an alkaloid present in cocoa beans. In a sample of dark chocolate there are 6.45 × 10 20 molecules of theobromine present. How many milligrams of theobromine are present in the sample? The molecular formula for theobromine is C 7 H 8 N 4 O 2 .

Answer 1

Answer: 193 mg of theobromine are present in the sample.

Explanation:

According to avogadro's law, 1 mole of every substance occupies 22.4 L at STP and contains avogadro's number of particles.

To calculate the moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given molecules}}{\text {Avogadros number}}=\frac{6.45\times 10^{20}}{6.023\times 10^{23}}=1.07\times 10^{-3}moles$

1 mole of theobromine $(C_7H_8N_4O_2)$ weigh = 180 g

$1.07\times 10^{-3}moles$  of theobromine $(C_7H_8N_4O_2)$ weigh = $\frac{180}{1}\times 1.07\times 10^{-3}=0.193g=193mg$   (1g=1000mg)

193 mg of theobromine are present in the sample.