Calculate the percentage composition of oxygen in calcium trioxocarbonate(IV) [Ca=40, C=12, O=16]

1. Analyze the Question

We need to find the percentage by mass of oxygen in calcium trioxocarbonate(IV), which is commonly known as calcium carbonate ($CaCO_3$). We are given the relative atomic masses: $Ca = 40$, $C = 12$, and $O = 16$.

2. Explain the Concept

To calculate the percentage composition of an element in a compound, we use the formula:

3. Show the Solution

Step 1: Calculate the molar mass of $CaCO_3$

• $Ca = 40$
• $C = 12$
• $O = 16 \times 3 = 48$ (since there are 3 atoms of oxygen)

Step 2: Calculate the percentage of oxygen The total mass of oxygen in the compound is $48$.

Note: While the question asks for the percentage composition, the options provided (16, 48, 40, 12) represent the numerical value of the mass contribution of oxygen in the formula unit. Based on the calculation, 48 is the correct value.

4. Identify the Answer

Comparing our result to the options provided, the correct value is 48.

5. Exam Tip

When calculating percentage composition, always double-check the number of atoms of the element in the chemical formula. A common mistake is forgetting to multiply the atomic mass of oxygen by its subscript (in this case, 3). Also, remember that the sum of the percentages of all elements in a compound must always equal 100%.