The percentage mass of magnesium in chlorophyll is 2.68% The number of magnesium atoms in 2 g of chlorophyll is _____________

Answer

To find the number of magnesium atoms in 2 g of chlorophyll, we will follow these steps:

### Step 1: Understand the composition of chlorophyll
The molecular formula of chlorophyll is C₅₅H₇₂O₅N₄Mg. This indicates that chlorophyll contains one magnesium (Mg) atom per molecule.

### Step 2: Calculate the molar mass of chlorophyll
To calculate the molar mass of chlorophyll, we will sum the atomic masses of all the atoms in the formula:
- Carbon (C): 55 atoms × 12 g/mol = 660 g/mol
- Hydrogen (H): 72 atoms × 1 g/mol = 72 g/mol
- Oxygen (O): 5 atoms × 16 g/mol = 80 g/mol
- Nitrogen (N): 4 atoms × 14 g/mol = 56 g/mol
- Magnesium (Mg): 1 atom × 24 g/mol = 24 g/mol

Now, we add these values together:
\[ \text{Molar mass of chlorophyll} = 660 + 72 + 80 + 56 + 24 = 892 \text{ g/mol} \]

### Step 3: Determine the number of moles of chlorophyll in 2 g
To find the number of moles of chlorophyll in 2 g, we use the formula:
\[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \]
Substituting the values:
\[ \text{Number of moles} = \frac{2 \text{ g}}{892 \text{ g/mol}} \approx 0.00224 \text{ moles} \]

### Step 4: Calculate the number of magnesium atoms
Since there is one magnesium atom per molecule of chlorophyll, the number of magnesium atoms can be found by multiplying the number of moles of chlorophyll by Avogadro's number (6.02 × 10²³ atoms/mol):
\[ \text{Number of magnesium atoms} = \text{Number of moles} \times \text{Avogadro's number} \]
Substituting the values:
\[ \text{Number of magnesium atoms} = 0.00224 \text{ moles} \times 6.02 \times 10^{23} \text{ atoms/mol} \approx 1.35 \times 10^{21} \text{ atoms} \]

### Final Answer
The number of magnesium atoms in 2 g of chlorophyll is approximately \( 1.35 \times 10^{21} \) atoms.

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