Atomic mass of (Mg = 24.3 and CI = 35.5) Molar mass of MgCl2 is 95.3 g/mol 1- Calculate the percent composition of magnesium chloride theoretically? Law for percent composition theoretically is: 1- For Mg= 2- For Cl 2- Calculate the percent composition of magnesium chloride experimentally? Law for percent composition experimentally is: 1- For Mg= 2- For Cl =
The Correct Answer and Explanation is:
To calculate the percent composition of magnesium chloride (MgCl₂), we will use both the theoretical method and the experimental method as requested.
1. Theoretical Percent Composition of MgCl₂
Given:
- Atomic mass of Mg = 24.3 g/mol
- Atomic mass of Cl = 35.5 g/mol
- Molar mass of MgCl₂ = 95.3 g/mol
Formula for Percent Composition Theoretically:Percent composition of element=(mass of element in 1 mole of compoundmolar mass of compound)×100\text{Percent composition of element} = \left( \frac{\text{mass of element in 1 mole of compound}}{\text{molar mass of compound}} \right) \times 100Percent composition of element=(molar mass of compoundmass of element in 1 mole of compound)×100
For Mg:(24.395.3)×100=25.5%\left( \frac{24.3}{95.3} \right) \times 100 = 25.5\%(95.324.3)×100=25.5%
For Cl:(2×35.595.3)×100=(71.095.3)×100=74.5%\left( \frac{2 \times 35.5}{95.3} \right) \times 100 = \left( \frac{71.0}{95.3} \right) \times 100 = 74.5\%(95.32×35.5)×100=(95.371.0)×100=74.5%
2. Experimental Percent Composition of MgCl₂
Law for Percent Composition Experimentally:Percent composition=(mass of element obtained experimentallymass of compound used)×100\text{Percent composition} = \left( \frac{\text{mass of element obtained experimentally}}{\text{mass of compound used}} \right) \times 100Percent composition=(mass of compound usedmass of element obtained experimentally)×100
To compute this experimentally, you need the actual mass of magnesium and chlorine recovered or measured from a sample of magnesium chloride.
Assume:
- Mass of Mg recovered = 2.43 g
- Mass of Cl recovered = 7.10 g
- Total mass of MgCl₂ used = 9.53 g
For Mg:(2.439.53)×100=25.5%\left( \frac{2.43}{9.53} \right) \times 100 = 25.5\%(9.532.43)×100=25.5%
For Cl:(7.109.53)×100=74.5%\left( \frac{7.10}{9.53} \right) \times 100 = 74.5\%(9.537.10)×100=74.5%
Explanation
Percent composition refers to the percentage by mass of each element in a compound. Theoretically, it is calculated using the known atomic masses and the compound’s molar mass. For magnesium chloride (MgCl₂), we first find the mass of each element in one mole of the compound. Magnesium contributes 24.3 g/mol while chlorine contributes twice its atomic mass, which is 2 × 35.5 = 71.0 g/mol. The total molar mass is 95.3 g/mol. To find the percentage of each element, divide the mass of the element by the total molar mass and multiply by 100. This gives 25.5 percent magnesium and 74.5 percent chlorine theoretically.
Experimentally, the same formula is used, but instead of using atomic masses, actual lab data is used. This might include the measured mass of magnesium and chlorine separated or obtained from a sample of magnesium chloride. For example, if a 9.53 g sample yields 2.43 g of magnesium and 7.10 g of chlorine, you calculate the percent composition using the same formula. The result matches the theoretical values if the experiment is accurate and there is minimal error.
Both approaches are useful in chemistry. Theoretical calculations are based on ideal chemical ratios, while experimental methods reflect real-world results and help identify purity, measurement accuracy, or the presence of impurities. Comparing both helps validate experimental results.
