How do I convert grams to moles to mole ratios? #"Mg" + "O"_2 -> "MgO"# 16.2g+10.67g=26.86g

1 Answer
Mar 22, 2017

Answer:

Here's how you can do that.

Explanation:

For starters, make sure that the chemical equation is balanced

#color(blue)(2)"Mg"_ ((s)) + "O"_ (2(g)) -> color(purple)(2)"MgO"_ ((s))#

Notice that the reaction consumes #color(blue)(2)# moles of magnesium and #1# mole of oxygen gas and produces #color(purple)(2)# moles of magnesium oxide.

You can thus say that the number of moles of each chemical species that takes part in this reaction must satisfy

#"moles Mg " : " moles O"_2color(white)(.): " moles MgO"#

#color(white)(aaaacolor(blue)(2)aaaa. color(black)(":") aaaacolor(black)(1) aaaaacolor(black)(":") aaaaacolor(purple)(2)#

Now, you can convert grams to moles by using molar mass. In this case, you have

#M_ ("M Mg") = "24.3050 g mol"^(-1)#

#M_ ("M O"_2) = "32.0 g mol"^(-1)#

#M_ ("MgO") = "40.3050 g mol"^(-1)#

So, to convert the mass of magnesium from grams to simply, use the element's molar mass as a conversion factor

#16.2 color(red)(cancel(color(black)("g"))) * "1 mole Mg"/(24.3050 color(red)(cancel(color(black)("g")))) = "0.6665 moles Mg"#

Do the same for the sample of oxygen gas.

#10.67 color(red)(cancel(color(black)("g"))) * "1 mole O"_2/(32.0color(red)(cancel(color(black)("g")))) = "0.3334 moles O"_2#

Finally, do the same for the magnesium oxide.

#26.86 color(red)(cancel(color(black)("g"))) * "1 mole MgO"/(40.3050color(red)(cancel(color(black)("g")))) = "0.6664 moles MgO"#

So, you know that when #0.6665# moles of magnesium react with #0.3334# moles of oxygen gas, you get #0.6664# moles of magnesium oxide.

The values are not an exact match because of rounding and of the values used for the molar masses of the three chemical species.