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Moles

Converting Mass into Moles and Moles into Mass.

The equation which converts mass into moles is

moles = mass ÷ RFM.

Mass refers to the mass of whatever they give you in the question.
RFM is the relative formula mass of a compound
(or use the relative atomic mass if it is an element).

Example 1.

How many moles are there in 35 grams of calcium carbonate?

The RFM of calcium carbonate is 100.

moles = mass ÷ RFM

moles = 35 ÷ 100
= 0·35 moles of calcium carbonate.

Example 2
.

How many moles are there in 125 grams of carbon?

The RAM of carbon is 12.

moles = mass ÷ RAM

moles = 125 ÷ 12
= 10·42 moles of carbon.

The equation can be rearranged to convert moles into mass

mass = moles x RFM.

Example 3
.

How many grams are there in 42 moles of neon?

The RAM of neon is 20.

mass = moles x RAM

mass = 42 x 20
= 840 grams of neon.

Example 4
.

How many grams are there in 5·67 moles of carbon dioxide?

The RFM of carbon dioxide is 44.

mass = moles x RAM

mass = 5·67 x 44
= 249·48 grams of carbon dioxide.

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