Chlorophyll, the green colouring matter of plants contains 2.68% of magnesium by mass. Calculate the number of magnesium atoms present in 2.5 g of chlorophyll.

Answer

To calculate the number of magnesium atoms present in 2.5 g of chlorophyll, we can follow these steps:

### Step 1: Calculate the mass of magnesium in 2.5 g of chlorophyll
Given that chlorophyll contains 2.68% magnesium by mass, we can find the mass of magnesium in 2.5 g of chlorophyll using the formula:

\[ \text{Mass of magnesium} = \left( \frac{\text{Percentage of magnesium}}{100} \right) \times \text{Mass of chlorophyll} \]

Substituting the values:

\[ \text{Mass of magnesium} = \left( \frac{2.68}{100} \right) \times 2.5 \, \text{g} = 0.067 \, \text{g} \]

### Step 2: Calculate the number of moles of magnesium
Next, we need to calculate the number of moles of magnesium using its molar mass. The molar mass of magnesium (Mg) is approximately 24 g/mol. The number of moles can be calculated using the formula:

\[ \text{Number of moles} = \frac{\text{Mass of magnesium}}{\text{Molar mass of magnesium}} \]

Substituting the values:

\[ \text{Number of moles of magnesium} = \frac{0.067 \, \text{g}}{24 \, \text{g/mol}} \approx 0.00279 \, \text{mol} \]

### Step 3: Calculate the number of magnesium atoms
To find the number of atoms, we can use Avogadro's number, which is \(6.022 \times 10^{23}\) particles/mol. The number of atoms can be calculated using the formula:

\[ \text{Number of atoms} = \text{Number of moles} \times \text{Avogadro's number} \]

Substituting the values:

\[ \text{Number of atoms} = 0.00279 \, \text{mol} \times 6.022 \times 10^{23} \, \text{atoms/mol} \approx 1.68 \times 10^{21} \, \text{atoms} \]

### Final Answer
The number of magnesium atoms present in 2.5 g of chlorophyll is approximately \(1.68 \times 10^{21}\) atoms.

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