Question #6b970

1 Answer
Stefan V.
Apr 8, 2015

The mass of the magnesium hydroxide present in the tablet is #"1 g"#.

So, you know that each tablet contains 500 mg of magnesium. However, this magnesium is actually a part of magnesium hydroxide, #Mg(OH)_2#.

To see how much magnesium hydroxide you have in every tablet, you must first determine the percentage by mass magnesium has in #Mg(OH)_2#. To do this, use their respective molar masses

#(24.3050cancel("g/mol"))/(58.3197cancel("g/mol")) * 100 = "41.68%"#

This means that you get 41.68 g of magnesium for every 100 g of #Mg(OH)_2#. As a result, 500 mg of magnesium would correspond to

#500 * 10^(-3)cancel("g Mg") * ("100 g "Mg(OH)_2)/(41.68cancel("g Mg")) = "1.199 g "Mg(OH)_2#

Rounded to one sig fig, the number of sig figs given for 500 mg, the answer will be

#m_(Mg(OH)_2) = color(green)("1 g")#

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