Longer Questions. Show all your calculations clearly and use the correct units a

Question

Longer Questions. Show all your calculations clearly and use the correct units and correct number of significant figures. A 500 mg tablet containing an antacid mixture of aluminum hydroxide, magnesium hydroxide, and inert material was dissolved in 50.0 mL of 0.500 M HCl solution. The resulting solution, which was still acidic, required-26.5 mL of 0.377 M NaOH for neutralization. How many moles of OH- were in the tablet? If the tablet contained equal moles of aluminium hydroxide and magnesium hydroxide, how many grams of each were in the tablet?

Explanation / Answer

(a) moles of OH- in the tablet

moles of HCl used = 0.5 x 0.05 = 0.025 mols

moles of NaOH required for neutralization = 0.377 M x 0.0265 L = 9.9905 x 10^-3 mols

moles of NaOH in the tablet = 0.025 - 9.9905 x 10^-5 = 0.015 mols

(b) If equal amounts of Al(OH)3 and Mg(OH)2 were present in tablet

total moles of [Al(OH)3 + Mg(OH)3] = 0.015/5 = 3 x 10^-3 mols

mass of Al(OH)3 in tablet = (3 x 10^-3/2) x 78.0036 = 0.117 g

mass of Mg(OH)2 in tablet = (3 x 10^-3/2) x 58.3197 = 0.0875 g

moles of Al(OH)3 = 0.0075/3 = moles

moles of Mg(OH)2 = (2/5) x 0.015 = 6 x 10^-3 mols

mass of Al(OH)3 in tablet = 9 x 10^-3 mol x 78.0036 g/mol = 0.70 g

mass of Mg(OH)2 = 6 x 10^-3 mol x 58.3197 g/mol = 0.35 g

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