To calculate the mass of KOH (potassium hydroxide) in a given volume of a semi-molar aqueous solution, we need to know the molarity of the solution. The term "semi-molar" is not a standard concentration unit and could refer to various concentrations. However, assuming it refers to a 0.5 molar (M) solution of KOH, we can proceed with the calculation.
The molar mass of KOH can be calculated by adding the atomic masses of its constituents:
- Potassium (K) has an atomic mass of approximately 39.10 grams/mol.
- Oxygen (O) has an atomic mass of approximately 16.00 grams/mol.
- Hydrogen (H) has an atomic mass of approximately 1.01 grams/mol.
So, the molar mass of KOH is: 39.10 g/mol (K) + 16.00 g/mol (O) + 1.01 g/mol (H) = 56.11 g/mol
Now, to calculate the mass of KOH in the solution:
Determine the number of moles of KOH in the solution using the molarity (M) and volume (V) relationship: Moles of KOH = Molarity (M) × Volume (L)
Since the given volume is in cm³, we need to convert it to liters: Volume (L) = 150 cm³ ÷ 1000 = 0.150 L
Moles of KOH = 0.5 M × 0.150 L = 0.075 moles
Calculate the mass of KOH using the moles and molar mass: Mass (g) = Moles × Molar mass
Mass of KOH = 0.075 moles × 56.11 g/mol ≈ 4.21 grams
Therefore, the mass of KOH in 150 cm³ of a semi-molar (0.5 M) aqueous solution is approximately 4.21 grams.