moles to grams


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The molar mass of a substance is the mass of one moles of the substance

For exampel;Ethanol whose molar mass is C2H6O has a molecular mass of 46.1 amu

Now we know how to find the mass of one mole of substance,there two important questions to ask.First,how much does a given number of moles of a substance weight?Second,how many moles of a given formula unit does a given mass of  substance contains?Both questions are easily answered using dimensional analysis or the conversion -factor method.


To illustrate,consider the conversion of moles of ethanol to mass in grams of ethanol

1 mol C2H5OH = 46.1 g C2H5OH

Thus,the factor converting moles of ethanol to grams of ethanol is  46.1 g C2H5OH/ 1 mol C2H5OH.Note that the unit you are converting from is one the bottim of the conversion factor; the unit you are converting to is on the top.

For example: Determine the grams of zinc iodide from the 0.0654 mol of ZnI2.

Solution: Use the formula weight of  znI2 to write the factor that converts from mol of ZnI2 to g ZnI2.Note that the unit you are converting from is on the bottom of the conversion factor.

Molar mass of ZnI2 is 319 amu, (which is obtained by summing the atomic weight in the formula).Therefore,

1 mol ZnI2 = 319 amu

conversion factors are :  1 mol ZnI2/319 g ZnI2   or 319 g ZnI2/ 1 mol ZnI2

given x conversion factor

0.0654 mol ZnI2 x   319 g ZnI2/ 1 mol ZnI2  = 20.9 g ZnI2