Question 18 A chemist must prepare of sodium hydroxide solution with a pH of at . He will do this in three steps: Fill a volumetric flask about halfway with distilled water. Weigh out a small amount of solid sodium hydroxide and add it to the flask. Fill the flask to the mark with distilled water. Calculate the mass of sodium hydroxide that the chemist must weigh out in the second step. Round your answer to significant digits.

9.0 g

Explanation:

There is some info missing. I think this is the original question.

A chemist must prepare 0.9 L of sodium hydroxide solution with a pH of 13.40 at 25°C. He will do this in three steps: Fill a volumetric flask about halfway with distilled water. Weigh out a small amount of solid sodium hydroxide and add it to the flask. Fill the flask to the mark with distilled water. Calculate the mass of sodium hydroxide that the chemist must weigh out in the second step. Round your answer to 2 significant digits.

Step 1: Calculate the pOH

We use the following expression.

pH + pOH = 14.00

pOH = 14.00 - pH = 14.00 - 13.40 = 0.60

Step 2: Calculate [OH⁻]

We use the following expression.

pOH = -log [OH⁻]

[OH⁻] = antilog -pOH = antilog -0.60 = 0.25 M

Step 3: Calculate [NaOH]

NaOH is a strong base that releases 1 OH⁻. Then, [NaOH] = 0.25 M

Step 4: Calculate the mass of NaOH

The molar mass of NaOH is 40.00 g/mol. The mass required to prepare 0.9 L of a 0.25 M solution is:

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