Question

How would you prepare 2000 mL of 0.15 M NaOH aqueous solution?

• A. Dissolve 12 g of NaOH in distilled water and dilute to 2000 mL
• B. Dissolve 15 g of NaOH in distilled water and dilute to 2000 mL
• C. Dissolve 10 g of NaOH in distilled water and dilute to 2000 mL
• D. Dissolve 7.5 g of NaOH in distilled water and dilute to 2000 mL

Answer 1

The Correct Option is A

To prepare 2000 mL of a 0.15 M NaOH aqueous solution, we need to first understand the concept of molarity. Molarity (M) is defined as the number of moles of solute per liter of solution. Here, we need a 0.15 M solution, which means 0.15 moles of NaOH in 1 liter (1000 mL) of solution.

1. First, calculate the moles of NaOH needed for 2000 mL (2 liters) of a 0.15 M solution: 
   \(\text{Moles of NaOH} = \text{Molarity} \times \text{Volume in liters} = 0.15 \, \text{M} \times 2 \, \text{L} = 0.3 \, \text{moles}\)
2. Next, convert moles of NaOH to grams. We do this using the molar mass of NaOH:
   • Molecular weight of NaOH: Na = 23 g/mol, O = 16 g/mol, H = 1 g/mol
   • \(\text{Molar mass of NaOH} = 23 + 16 + 1 = 40 \, \text{g/mol}\)
3. Calculate the mass of NaOH required: 
   \(\text{Mass of NaOH} = \text{Moles} \times \text{Molar mass} = 0.3 \, \text{moles} \times 40 \, \text{g/mol} = 12 \, \text{g}\)
4. Dissolve 12 g of NaOH in distilled water and then dilute the solution to a total volume of 2000 mL (2 liters).

The correct option is to dissolve 12 g of NaOH in distilled water and dilute it to 2000 mL volume. This option corresponds to the calculation, matching the correct molarity and volume requirements for the solution.