A sample of ammonium phosphate, `(NH_4)_3PO_4` contains 18 moles of hydrogen atoms. The number of moles of oxygen atoms in the sample is

Options

A. 6
B. 18
C. 4
D. 24

Answer

To solve the problem, we need to determine the number of moles of oxygen atoms in a sample of ammonium phosphate, `(NH₄)₃PO₄`, given that the sample contains 18 moles of hydrogen atoms.

### Step-by-Step Solution:

1. **Identify the Composition of Ammonium Phosphate**:
The chemical formula for ammonium phosphate is `(NH₄)₃PO₄`. From this formula, we can determine the number of hydrogen atoms and oxygen atoms in one mole of ammonium phosphate.

- Each ammonium ion `(NH₄)⁺` contains 4 hydrogen atoms.
- Since there are 3 ammonium ions, the total number of hydrogen atoms in one mole of ammonium phosphate is:
\[ 4 \text{ H atoms/ion} \times 3 \text{ ions} = 12 \text{ H atoms} \]
- The phosphate ion `(PO₄)³⁻` contains 4 oxygen atoms.

2. **Establish the Ratio of Hydrogen to Oxygen**:
In one mole of ammonium phosphate, we have:
- 12 moles of hydrogen atoms
- 4 moles of oxygen atoms

3. **Set Up the Proportion**:
We know that 12 moles of hydrogen correspond to 4 moles of oxygen. We can set up a proportion to find out how many moles of oxygen correspond to 18 moles of hydrogen:
\[ \frac{12 \text{ H}}{4 \text{ O}} = \frac{18 \text{ H}}{x \text{ O}} \]
Where \( x \) is the number of moles of oxygen atoms we want to find.

4. **Cross-Multiply and Solve for \( x \)**:
Cross-multiplying gives us:
\[ 12x = 4 \times 18 \]
\[ 12x = 72 \]
Now, divide both sides by 12:
\[ x = \frac{72}{12} = 6 \]

5. **Conclusion**:
The number of moles of oxygen atoms in the sample is 6.

### Final Answer:
The number of moles of oxygen atoms in the sample is **6 moles**.