Question

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

Answer 1

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.