[choyaoov]

A 0.05895-g sample of impure magnesium hydroxide is dissolved in 100.0 mL of 0.2050 M HCL solution. The excess acid then needs 19.85 mL of 0.1020 M NaOH for neutralization. Calculate the percent by mass of magnesium hydroxide in the sample, assuming that it is the only substance reacting with the HCL solution.

[enahs]

That is a good question. Why don't you give it a try first?