Question

calculate the mass of 1.204 x 10^{24} molecules of water.
3.600 g
9.000 g
36.00 g
90.00 g

Explanation:

Step1: Calculate the number of moles

Use Avogadro's number \(N_A = 6.02\times10^{23}\text{ molecules/mol}\).
The number of moles \(n=\frac{N}{N_A}\), where \(N = 1.204\times 10^{24}\text{ molecules}\).
\(n=\frac{1.204\times 10^{24}}{6.02\times 10^{23}} = 2\text{ mol}\)

Step2: Calculate the molar mass of water

The formula of water is \(H_2O\). The molar mass of \(H\) is \(1\text{ g/mol}\) and of \(O\) is \(16\text{ g/mol}\).
\(M=(2\times1 + 16)\text{ g/mol}=18\text{ g/mol}\)

Step3: Calculate the mass

Use the formula \(m = n\times M\).
\(m=2\text{ mol}\times18\text{ g/mol}=36\text{ g}\)

Answer:

36.00 g