Question

2 step conversion practice

1. how many atoms are in 88.2 g of lead (pb)?
2. how many atoms are in 156 g of gold (au)?
3. how many atoms are in 35.0 g of potassium (k)?
4. how many atoms are in 22.5 g of magnesium (mg)?

Explanation:

Question 9: How many atoms are in 88.2 g of lead (Pb)?

Step 1: Find moles of Pb

Molar mass of Pb is 207.2 g/mol. Moles = mass / molar mass.
$n = \frac{88.2\ \text{g}}{207.2\ \text{g/mol}} \approx 0.4257\ \text{mol}$

Step 2: Find number of atoms

Use Avogadro's number ($N_A = 6.022 \times 10^{23}\ \text{atoms/mol}$). Atoms = moles × $N_A$.
$N = 0.4257\ \text{mol} \times 6.022 \times 10^{23}\ \text{atoms/mol} \approx 2.56 \times 10^{23}\ \text{atoms}$

Step 1: Find moles of Au

Molar mass of Au is 196.97 g/mol. Moles = mass / molar mass.
$n = \frac{156\ \text{g}}{196.97\ \text{g/mol}} \approx 0.792\ \text{mol}$

Step 2: Find number of atoms

Use Avogadro's number. Atoms = moles × $N_A$.
$N = 0.792\ \text{mol} \times 6.022 \times 10^{23}\ \text{atoms/mol} \approx 4.77 \times 10^{23}\ \text{atoms}$

Step 1: Find moles of K

Molar mass of K is 39.10 g/mol. Moles = mass / molar mass.
$n = \frac{35.0\ \text{g}}{39.10\ \text{g/mol}} \approx 0.895\ \text{mol}$

Step 2: Find number of atoms

Use Avogadro's number. Atoms = moles × $N_A$.
$N = 0.895\ \text{mol} \times 6.022 \times 10^{23}\ \text{atoms/mol} \approx 5.39 \times 10^{23}\ \text{atoms}$

Answer:

$\approx 2.56 \times 10^{23}$ atoms

Question 10: How many atoms are in 156 g of gold (Au)?