# Mole quick question

Hi, when using the mole equation (mole = mass/Mr) does the mass have to be in grams or does it not matter as long as all the masses are in consistent units?
Original post by subbhy
Hi, when using the mole equation (mole = mass/Mr) does the mass have to be in grams or does it not matter as long as all the masses are in consistent units?

grams
Original post by charco
grams

Why would it matter if it was in kg or tonnes?

As long as I know that it is
Original post by subbhy
Why would it matter if it was in kg or tonnes?

As long as I know that it is

Because the relative masses are in g mol^-1 and so to get the moles from the equation, the mass must be in grams so the g’s cancel.

Let’s try inputting the units of mass and Mr into the formula moles = mass/Mr

(g)/(g mol^-1) = 1/(mol^-1) = mol
(edited 5 months ago)
Original post by TypicalNerd
Because the relative masses are in g mol^-1 and so to get the moles from the equation, the mass must be in grams so the g’s cancel.

Let’s try inputting the units of mass and Mr into the formula moles = mass/Mr

(g)/(g mol^-1) = 1/(mol^-1) = mol

Ah okay thank you
Original post by TypicalNerd
Because the relative masses are in g mol^-1 and so to get the moles from the equation, the mass must be in grams so the g’s cancel.

Let’s try inputting the units of mass and Mr into the formula moles = mass/Mr

(g)/(g mol^-1) = 1/(mol^-1) = mol

My teacher said you will still get the same answer but it should be in gens