Question

1. how many atoms of iron are in 72.5 grams?
2. how many formula units of al(no₃)₃ are in.360 moles?
3. how many grams of magnesium chloride are in 1.8066 × 10²⁴ formula units?
4. how many grams are in.800 moles of calcium nitrate?
5. how many moles are in 65 grams of carbon dioxide?
6. how many grams are in 6.54 × 10²³ formula units of na₂so₄?
7. how many sodium ions are in 3.0 moles of sodium oxide?
8. how many total atoms are present in 0.829 moles of k₂so₄?

Explanation:

Problem 3: How many atoms of iron are in 72.5 grams?

Step 1: Find molar mass of Fe

Molar mass of Fe is 55.85 g/mol.

Step 2: Calculate moles of Fe

Moles = $\frac{\text{mass}}{\text{molar mass}}$ = $\frac{72.5\ \text{g}}{55.85\ \text{g/mol}}$ ≈ 1.298 mol.

Step 3: Calculate number of atoms

Using Avogadro's number ($N_A = 6.022\times10^{23}\ \text{atoms/mol}$), number of atoms = moles × $N_A$ = 1.298 mol × $6.022\times10^{23}\ \text{atoms/mol}$ ≈ $7.82\times10^{23}$ atoms.

Step 1: Use Avogadro's number

Number of formula units = moles × $N_A$, where $N_A = 6.022\times10^{23}\ \text{formula units/mol}$.

Step 2: Calculate

Number of formula units = 0.360 mol × $6.022\times10^{23}\ \text{formula units/mol}$ ≈ $2.17\times10^{23}$ formula units.

Step 1: Find moles of $\text{MgCl}_2$

Moles = $\frac{\text{number of formula units}}{N_A}$ = $\frac{1.8066\times10^{24}\ \text{formula units}}{6.022\times10^{23}\ \text{formula units/mol}}$ = 3.0 mol.

Step 2: Find molar mass of $\text{MgCl}_2$

Molar mass of $\text{MgCl}_2$ = 24.31 (Mg) + 2×35.45 (Cl) = 24.31 + 70.90 = 95.21 g/mol.

Step 3: Calculate mass

Mass = moles × molar mass = 3.0 mol × 95.21 g/mol = 285.63 g ≈ 286 g.

Answer:

Approximately $7.82\times10^{23}$ atoms of iron.

Problem 4: How many formula units of $\text{Al(NO}_3\text{)}_3$ are in 0.360 moles?