Questions: CHEMISTRY 1104 1. A 100.0 g sample of zinc contains: a) how many moles of zinc? b) how many atoms of zinc? 2. What is the mass in grams of 0.250 moles of Na2CO3?

Solution Steps

To find the number of moles of zinc in a 100.0 g sample, we use the molar mass of zinc. The molar mass of zinc (Zn) is approximately 65.38 g/mol.

\[ \text{Moles of Zn} = \frac{\text{mass of Zn}}{\text{molar mass of Zn}} = \frac{100.0 \, \text{g}}{65.38 \, \text{g/mol}} \]

\[ \text{Moles of Zn} \approx 1.529 \, \text{mol} \]

To find the number of atoms, we use Avogadro's number, which is \(6.022 \times 10^{23}\) atoms/mol.

\[ \text{Atoms of Zn} = \text{moles of Zn} \times \text{Avogadro's number} = 1.529 \, \text{mol} \times 6.022 \times 10^{23} \, \text{atoms/mol} \]

\[ \text{Atoms of Zn} \approx 9.204 \times 10^{23} \, \text{atoms} \]

First, we need to find the molar mass of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\). The molar masses of the elements are approximately: Na = 22.99 g/mol, C = 12.01 g/mol, O = 16.00 g/mol.

\[ \text{Molar mass of } \mathrm{Na}_{2} \mathrm{CO}_{3} = 2(22.99) + 12.01 + 3(16.00) = 105.99 \, \text{g/mol} \]

Now, calculate the mass of 0.250 moles:

\[ \text{Mass} = \text{moles} \times \text{molar mass} = 0.250 \, \text{mol} \times 105.99 \, \text{g/mol} \]

\[ \text{Mass} \approx 26.50 \, \text{g} \]

Final Answer