A chemist must prepare 500.0mL of hydrochloric acid solution with a pH of 0.90 at 25°C.

He will do this in three steps:

a. Fill a 500.0mL volumetric flask about halfway with distilled water.
b. Measure out a small volume of concentrated (7.0M) stock hydrochloric acid solution and add it to the flask.
c. Fill the flask to the mark with distilled water.

Calculate the volume of concentrated hydrochloric acid that the chemist must measure out in the second step. Round your answer to 2 significant digits.