The whole idea in dimensional analysis is to convert what you have into what you want. To make that happen you use a factor. The factor is then arranged so that the unit you don't want to keep (the unit you have) cancels and the unit you want to change to doesn't cancel. Example. Convert 10 inches to cm. You know there are 2.54 cm in 1 inch; therefore, the factor is EITHER 2.54 cm/1 in OR 1 in/2.54 cm. You use the one that cancels the unit you have and keeps the one you want.
10 inches x (factor) = ? cm
Since we have two ways for the factor let me show you what happens in each.
10 inches x (1 inch/2.54 cm) = 3.94 BUT LOOK AT THE UNITS. That's 3.94 inches^2/cm which is not what you want. You want inches in 10 inches to cancel and you want the answer to be in cm. So let's try the other way to place the factor. That's
10 inches x (2.54 cm/1 inch) = 25.4 and the unit is cm. Why? Because you see the inches unit in 10 inches in the numerator cancels with the inch unit in 1 inch in the denominator which leaves the unit cm all by itself and that's the unit for 25.4.
It makes no difference if you are converting mols to grams, inches to cm, mols to number of molecules, it's all done the same way; i.e.,
what you have x (factor) = what you want. Hope this helps.
Can anyone explain dimensional analysis to me like (grams to moles, avogadros number) and all those things. Im doing all the work but im obviously doing it wrong my answers are completely opposite of what they should be.
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