Question

Am I doing this right? What mass of `"HCl"` reacts with `"3.26 g"` of `"Mg"("OH")_2`?

`"3.26 g Mg"("OH")_2 xx ("1 mol Mg"("OH")_2)/("58.326 g Mg"("OH")_2) xx ("2 mol HCl")/("1 mol Mg"("OH")_2) xx "36.458 g HCl"/"1 mol HCl"`

`=` `"4.075 g"`

Answer 1

Here's what I would do. Since `"3.26 g"` of `"Mg"("OH")_2` neutralizes a certain amount of `"HCl"`, we start with that much mass of magnesium hydroxide and determine what mass of `"HCl"` it corresponds to.

The balanced equation is

`2"HCl"(aq) + "Mg"("OH")_2(s) -> 2"H"_2"O"(l) + "MgCl"_2(aq)`

So we use the general pathway

`"g Mg"("OH")_2 stackrel(-: "g/mol Mg"("OH")_2)(->) "mols Mg"("OH")_2 stackrel(xx "mol HCl"/("mol Mg"("OH")_2))(->) "mols HCl" stackrel(xx "g/mol HCl")(->) "g HCl"`

to write out

`3.26 cancel("g Mg"("OH")_2) xx cancel("1 mol Mg"("OH")_2)/(58.3188 cancel("g Mg"("OH")_2)) xx (2 cancel("mol HCl"))/cancel("1 mol Mg"("OH")_2) xx "36.4609 g HCl"/cancel"1 mol HCl"`

`=` `color(blue)("4.08 g HCl")`

It looks like your mathematical process is right, but you seem to have used slightly different molar masses.

I used `"35.453 g/mol Cl"`, `"1.0079 g/mol H"`, `"24.305 g/mol Mg"` and `"15.999 g/mol O"`. Other than that, you have it.