The retired chemistry professor in me sees a teaching moment here.
The "mole" is exactly analogous to the "dozen". The only difference is scale. A dozen is defined as 12 things. A mole is defined as "a very large number" of things; 6.022x10^23 (an Avagadro's number) of things to be exact.
If you want to build a dozen cars you would need (among other things) a dozen engines and four dozen wheels/tires. If you want to build a dozen methane molecules you would need a dozen carbon atoms and four dozen hydrogen atoms.
Making a dozen cars might make sense and it would be easy to count out the required number of parts as they are macroscopic.
Making a dozen methane molecules is silly... that amount of material is way too small to be useful. Furthermore atoms/molecules are too small to be counted individually (at least in any convenient manner).
So, instead of counting atoms/molecules individually, we use their mass and weigh out macroscopic collections of them. In order to do this we need to know the molar mass (the factor for converting between count, i.e. moles, and mass) of each type of atom or molecule.
Fortunately the molar mass is easy to determine if one has a periodic table. The molar mass of atoms is equal to their atomic weight which is listed on the periodic table. For molecules/compounds, just add the atomic masses of the components to arrive at the molar mass.
Thus 1 mole (12 g) of carbon plus 4 moles of hydrogen (4 x 1 g = 4 g) will yield 1 mole of methane which weighs 16 grams (12 + 4).
One could do the same thing with automobiles if one wanted as long as you know the weight of each component. If you know that engines weigh 200 kg each and wheel/tires weigh 25 kg each. Then the "dozen mass" of engines would be 2,400 kg (12x200) and the "dozen mass" of wheels/tires would be 300 kg (12x25).
Thus to make a dozen autos, you could weigh out 2,400 kg of engines and 300 kg of tires/wheels and you would know that you had enough of each to make a dozen autos.
Of course, if you simply follow photographic recipes one can ignore moles and just use the specified weights. It is not that moles are unimportant just that someone else has done the conversion from moles to grams for you.
The problem comes in if you want to make changes to a recipe. For instance, if you want to use a potassium salt instead of the sodium salt called for in the recipe. Now moles become important because the conversion factor (molar mass) changes.
To use the auto example, say you changed from tires/wheels weighing 25 kg each to fancy aluminum tire/wheels that weigh only 20 kg each. If you weighed out 300 kg of tires/wheels your would have 15 of them (300/20 = 15) instead of the dozen (12) you need.
This would be wasteful at a minimum. For a chemical reaction the excess (or deficit) of a particular component might well change the outcome of the reaction/procedure. Thus the need to adjust the recipe.
Hopefully... maybe?... this helps to explain the chemical concepts.
The "mole" is exactly analogous to the "dozen". The only difference is scale. A dozen is defined as 12 things. A mole is defined as "a very large number" of things; 6.022x10^23 (an Avagadro's number) of things to be exact.
If you want to build a dozen cars you would need (among other things) a dozen engines and four dozen wheels/tires. If you want to build a dozen methane molecules you would need a dozen carbon atoms and four dozen hydrogen atoms.
Making a dozen cars might make sense and it would be easy to count out the required number of parts as they are macroscopic.
Making a dozen methane molecules is silly... that amount of material is way too small to be useful. Furthermore atoms/molecules are too small to be counted individually (at least in any convenient manner).
So, instead of counting atoms/molecules individually, we use their mass and weigh out macroscopic collections of them. In order to do this we need to know the molar mass (the factor for converting between count, i.e. moles, and mass) of each type of atom or molecule.
Fortunately the molar mass is easy to determine if one has a periodic table. The molar mass of atoms is equal to their atomic weight which is listed on the periodic table. For molecules/compounds, just add the atomic masses of the components to arrive at the molar mass.
Thus 1 mole (12 g) of carbon plus 4 moles of hydrogen (4 x 1 g = 4 g) will yield 1 mole of methane which weighs 16 grams (12 + 4).
One could do the same thing with automobiles if one wanted as long as you know the weight of each component. If you know that engines weigh 200 kg each and wheel/tires weigh 25 kg each. Then the "dozen mass" of engines would be 2,400 kg (12x200) and the "dozen mass" of wheels/tires would be 300 kg (12x25).
Thus to make a dozen autos, you could weigh out 2,400 kg of engines and 300 kg of tires/wheels and you would know that you had enough of each to make a dozen autos.
Of course, if you simply follow photographic recipes one can ignore moles and just use the specified weights. It is not that moles are unimportant just that someone else has done the conversion from moles to grams for you.
The problem comes in if you want to make changes to a recipe. For instance, if you want to use a potassium salt instead of the sodium salt called for in the recipe. Now moles become important because the conversion factor (molar mass) changes.
To use the auto example, say you changed from tires/wheels weighing 25 kg each to fancy aluminum tire/wheels that weigh only 20 kg each. If you weighed out 300 kg of tires/wheels your would have 15 of them (300/20 = 15) instead of the dozen (12) you need.
This would be wasteful at a minimum. For a chemical reaction the excess (or deficit) of a particular component might well change the outcome of the reaction/procedure. Thus the need to adjust the recipe.
Hopefully... maybe?... this helps to explain the chemical concepts.