An antacid tablet containing magnesium hydroxide instead of calcium carbonate was dissolved in 100.0 mL of 0.2893 M HCL. 10 mL of this solutions was titrated to endpoint with 25.20 mL of 0.1007 M NaOH. How much magnesium hydroxide was in the antacid tablet(in mg)?

Question

Any help is appreciated

Answer 1

Mg(OH)2 + 2HCl ==> MgCl2 + 2H2O

millimols HCl added = mL x M = 100 x 0.2893M = 28.93 total acid added.

mmols HCl not used = 25.20 mL x 0.1007 = 2.538 for a 10 mL portion of the above acid; therefore, if 100 mL had been titrated you would have used 25.38 mmols NaOH which corresponds to 25.38 mmols acid not used. So how much acid was used.
begin = 28.93
-not used = 25.38
----------------
used = 3.55 mmols.
3.55 mmols acid used = 1/2 that for mmols Mg(OH)2 in the sample. Convert that to grams if you want to know grams Mg(OH)2 in one tablet.