im needing help on my chemistry .... chemical reactions and moles.

Question

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

that's the balanced equation.

question 1. If one antacid tablet contains 0.10 g of Magnesium hydroxide how many grams of stomach acid does this tablet neutralize?

question 2. How many grams of hydrochloric acid would be neutralized if 0.700 mole of water is produced?

Im having a hard time figuring out the answers and understanding

Answer 1

So, you have the balanced equation: Mg(OH)₂ + 2HCl ==> MgCl₂ +2H₂O

You MUST understand what this balanced equation tells you. It tells you that ONE MOLE of Mg(OH)2 reacts with TWO MOLES of HCl to produce ONE MOLE of MgCl₂ and TWO MOLES of H₂O.

Knowing this, we can convert 0.10 g of magnesium hydroxide to moles, then determine moles of HCl that will react with that many moles of magnesium hydroxide, and finally convert that to grams of HCl. All this will be done using the MOLE RATIOS described in the balanced equation. So, here we go....

0.10 g Mg(OH)2 x 1 mole Mg(OH)2/58.32 g = 0.001715 MOLES Mg(OH)2

MOLES HCl reacting: 0.001715 moles Mg(OH)2 x 2 moles HCl/1 mol Mg(OH)2 = 0.00343 MOLES HCl

GRAMS HCL reacting: 0.00343 moles HCl x 36.5 g/mole = 0.125 grams = 0.13 grams HCl (2 sig. figs.)

If 0.700 moles of H₂O are produced, the balanced equation tells us that 0.700 moles of HCl must have been used because 2 moles of H₂O are produced from 2 moles of HCl (see balanced equation). That's because they are in a 1 : 1 mole ratio. Looking at it using dimensional analysis, we have...

0.700 moles H₂O x 2 moles HCl/2 moles H₂O = 0.700 moles HCl

Grams HCl = 0.700 moles HCl x 36.5 g/mol = 25.6 grams of HCl neutralized