How many mol of carbon are in 30.7 g of potassium cyanide?
The correct answer and explanation is:
Correct Answer:
0.470 mol of carbon
Explanation:
To determine the number of moles of carbon in 30.7 grams of potassium cyanide (KCN), follow these steps:
Step 1: Determine the molar mass of KCN
KCN contains three elements:
- Potassium (K): 39.10 g/mol
- Carbon (C): 12.01 g/mol
- Nitrogen (N): 14.01 g/mol
Add the atomic masses:
39.10 + 12.01 + 14.01 = 65.12 g/mol
So, the molar mass of potassium cyanide is 65.12 g/mol.
Step 2: Calculate the number of moles of KCN in 30.7 g
Use the formula: moles of KCN=massmolar mass=30.7 g65.12 g/mol≈0.4716 mol\text{moles of KCN} = \frac{\text{mass}}{\text{molar mass}} = \frac{30.7\, \text{g}}{65.12\, \text{g/mol}} \approx 0.4716\, \text{mol}
Step 3: Use mole ratio to find moles of carbon
Each formula unit of KCN contains 1 atom of carbon. That means the number of moles of KCN is equal to the number of moles of carbon in the sample.
So, the number of moles of carbon = 0.4716 mol
Rounded to three significant figures, the final answer is:
0.470 mol of carbon
Why this works:
The molar mass of a compound allows conversion between mass and moles. Once the number of moles of the compound is known, the mole ratio from the chemical formula is used to determine how many moles of a specific element are present. Since KCN contains one carbon atom per molecule, the number of moles of KCN equals the number of moles of carbon atoms.