[FLgirl]

Question: Magnesium hydroxide, the active ingredient in milk of magnesia, neutralizes stomach acid, primarily HCl, according to the following reaction:

Mg(OH)2(aq) + 2 HCl(aq) ---> 2 H2O(l) + MgCl2(aq)

What mass of HCl, in grams, can be neutralized by a dose of milk of magnesia caontaining 3.26g Mg(OH)2?


My problem with the question: To be able to get the relationship between moles of magnesium hydroxide and moles of HCl, don't they need to be on opposite sides of the reaction? my book shows them that way, but not when they are both on one side. I tried solving it and got it wrong. Help?

[Arkcon]

No, they don't have to be on opposite sides of the equation.  They can ask you to relate grams, to moles, and back again, for something on the same side of the equation.  Just as they've done here, the HCl is neutralized (reacts to form a compund that no longer has the properties of an acid) with the magnesium hydroxide.  Lets see how you relate the grams to moles for each.

[FLgirl]

My attempt at a solution was this: 3.26g Mg(OH)2 X 1mol Mg(OH)2 /34.01g Mg(OH)2 X 2 mol HCl/ 1 mol Mg(OH)2 X 36.46g HCl/ 1 molg HCl = 6.99

but it was wrong!

[Borek]

Check your molar mass of Mg(OH)₂.

[EpicWinston]

Yea you made a mistake on the molar mass of Mg(OH)₂ recall that you have to take the subscript into account. The molar mass should have been 58.3

[FLgirl]

Thanks you guys. crucial little detail I messed up on..