To find the mass by mass percentage concentration of a solution, we can use the following formula: \[ \text{Mass by mass percentage} = \left( \frac{\text{mass of solute}}{\text{mass of solute} + \text{mass of solvent}} \right) \times 100 \] ### Step-by-Step Explanation: 1. **Identify the Masses**: - Mass of solute = 20 g - Mass of solvent (water) = 180 g 2. **Calculate the Total Mass of the Solution**: - Total mass of the solution = mass of solute + mass of solvent - Total mass = 20 g + 180 g = 200 g 3. **Apply the Formula**: - Now, substitute the values into the formula: \[ \text{Mass by mass percentage} = \left( \frac{20 \, \text{g}}{200 \, \text{g}} \right) \times 100 \] 4. **Perform the Calculation**: - First, calculate the fraction: \[ \frac{20 \, \text{g}}{200 \, \text{g}} = 0.1 \] - Now, multiply by 100 to convert it to a percentage: \[ 0.1 \times 100 = 10\% \] 5. **Final Answer**: - The mass by mass percentage concentration of the solution is **10%**. ### Explanation of Why Other Options Are Incorrect: - **Option A: 11%**: - This option is incorrect because it does not accurately reflect the calculation based on the given masses of solute and solvent. The calculation clearly shows that the percentage is 10%, not 11%. - **Option B: 22.2%**: - This option is also incorrect. It may arise from a misunderstanding of the formula or miscalculating the total mass. The correct calculation shows that the mass percentage is significantly lower than 22.2%. - **Option D: 20%**: - This option is incorrect as well. It might be confused with the mass of the solute alone, but the mass percentage must consider the total mass of the solution, which is 200 g. Thus, 20 g of solute in 200 g of solution does not yield 20%. ### Common Pitfalls: - **Not Adding Solute and Solvent Masses**: A common mistake is to forget to add the mass of the solute and solvent together before calculating the percentage. - **Confusing Mass Percentage with Other Concentration Units**: Ensure you are using the correct formula for mass by mass percentage, as there are other ways to express concentration (like molarity or volume percentage). ### Revision Summary: - The mass by mass percentage is calculated using the formula: \(\left( \frac{\text{mass of solute}}{\text{mass of solute} + \text{mass of solvent}} \right) \times 100\). - For this problem, the mass of solute is 20 g and the mass of solvent is 180 g, leading to a total mass of 200 g. - The final mass by mass percentage is 10%. - Always ensure to add the masses correctly and use the right formula to avoid common mistakes.