How can I find the actual percent composition of magnesium oxide?
1 Answer
Here's how you can do that.
Explanation:
A compound's percent composition essentially tells you how many grams of each constituent element you get per
#color(blue)(|bar(ul(color(white)(a/a)"% element i" = "mass of i"/"mass of compound" xx 100color(white)(a/a)|)))#
This means that in order to find a compound's percent composition, you need to pick a sample and use
- the total mass of the sample
- the mass of each constituent element in this sample
Now, magnesium oxide,
This will be your sample of magnesium oxide. Notice that one mole of magnesium oxide contains
- one mole of magnesium,
#1 xx "Mg"# - one mole of oxygen,
#1 xx "O"#
The molar masses of the two elements are
#M_("M Mg") = "24.3050 g mol"^(-1)#
#M_("M O") = "15.9994 g mol"^(-1)#
This tells you that one mole of magnesium oxide, i.e.
#"24.3050 g Mg" " "# and#" " "15.9994 g O"#
Now you have all that you need to figure out the percent composition of the compound. You will have
#"% Mg" = (24.3050 color(red)(cancel(color(black)("g"))))/(40.3044color(red)(cancel(color(black)("g")))) xx 100 = color(green)(|bar(ul(color(white)(a/a)color(black)("60.304 %")color(white)(a/a)|)))#
#"% O" = (15.9994color(red)(cancel(color(black)("g"))))/(40.3044color(red)(cancel(color(black)("g")))) * 100 = color(green)(|bar(ul(color(white)(a/a)color(black)("39.696 %")color(white)(a/a)|)))#
You can thus say that
#"60.304 g Mg" " "# and#" " "39.696 g O"#