How many moles are in a 42.5 g sample of magnesium oxide #MgO#?

Answer 1

Approx. #1.0*mol#

Oxygen has an atomic mass of #16.0*g*mol^-1#; magnesium has an atomic mass of #24.3*g*mol^-1#. We add these masses together, and we get a molar mass for #MgO# of #40.3*g*mol^-1#.

How many #MgO# formula units does such a mass represent?

To find the molar quantity, we simply divide the mass by the molar quantity, to get an answer in #"moles"#:

#"Moles of MgO"# #=# #(42.5*cancelg)/(40.3*cancelg*mol^-1)=1.05*mol#.

The answer is dimensionally consistent; we wanted an answer in moles. We got an answer in #1/(mol^-1)=1/(1/(mol))=mol# as required..........

How many formula units of #MgO# does such a mass represent?

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Answer 2

Jose Ayala

There are approximately 0.666 moles in a 42.5 g sample of magnesium oxide (MgO).

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.