21. What is the molar mass of potassium carbonate K_(2)CO_(3) 67g/mol 106g/mol 99g/mol 138g/mol

To calculate the molar mass of potassium carbonate, \( \mathrm{K}_{2} \mathrm{CO}_{3} \), we need to sum the molar masses of all the atoms in the compound:<br /><br />1. Potassium (K): The atomic mass of potassium is approximately \( 39.10 \, \mathrm{g/mol} \). Since there are two potassium atoms, the total mass contributed by potassium is:<br /> \[<br /> 2 \times 39.10 = 78.20 \, \mathrm{g/mol}<br /> \]<br /><br />2. Carbon (C): The atomic mass of carbon is approximately \( 12.01 \, \mathrm{g/mol} \).<br /><br />3. Oxygen (O): The atomic mass of oxygen is approximately \( 16.00 \, \mathrm{g/mol} \). Since there are three oxygen atoms, the total mass contributed by oxygen is:<br /> \[<br /> 3 \times 16.00 = 48.00 \, \mathrm{g/mol}<br /> \]<br /><br />Adding these together gives the molar mass of potassium carbonate:<br />\[<br />78.20 + 12.01 + 48.00 = 138.21 \, \mathrm{g/mol}<br />\]<br /><br />Therefore, the molar mass of \( \mathrm{K}_{2} \mathrm{CO}_{3} \) is approximately \( 138 \, \mathrm{g/mol} \).<br /><br />The correct answer is \( 138 \, \mathrm{g/mol} \).