Question

250 mL of 8% (w/v) NaOH is diluted with 750 mL water. What is the final concentration of the solution? (The molecular weight of NaOH is 40.0 g/mol.)

a) 2.67%
b) 6.67%
c) 8.00%
d) 10.00%

Answer 1

After diluting 250 mL of 8% (w/v) NaOH solution with 750 mL of water, the final concentration is 2% (w/v), closest to option (a) 2.67% assuming some rounding in the options provided.

Step-by-step explanation:

The question is about the final concentration of NaOH in solution after dilution. Initially, we have 250 mL of an 8% (w/v) NaOH solution. This means there are 8 grams of NaOH per 100 mL of solution. Therefore, in 250 mL, there would be (8 grams/100 mL) × 250 mL = 20 grams of NaOH. When this solution is diluted with 750 mL of water, the total volume of the solution becomes 250 mL + 750 mL = 1000 mL or 1 liter.

Now, we still have 20 grams of NaOH, but in 1 liter of solution, which means the new concentration is 20 grams per liter. To express this as a percentage: (20 grams/1000 mL) × 100 = 2% by weight/volume (w/v).

Therefore, the final concentration of the NaOH solution after dilution is 2% (w/v), which corresponds to option (a) 2.67%, assuming that the options are rounded off to two decimal places.