Molar mass

[yyh020635]

Why does the molar mass equals to the relative atomic mass of the element? I found that amazing when it's possible to know how many atoms are there in a certain amount of element. Can anyone explain in details?

 

Thanks in advance.

[Sensei]

Why does the molar mass equals to the relative atomic mass of the element?

 

Because molar mass was earlier.

The idea came from Amedeo Avogadro in 1811

http://en.wikipedia.org/wiki/Avogadro_constant

He didn't calculate Avogadro const, he just came up with idea.

Scientists calculate it hundred years later.

 

f.e.

take 18 grams of water, and 58-59 grams of NaCl, then pass current through it, and you will produce equal volumes of Hydrogen and Chlorine gases on electrodes, and 40 grams of NaOH will remain in container.

You don't even have to know what is Avogadro const.

 

Doing electrolysis of various materials/metals, you can calculate how much they lost mass. Electrodes are dissolved in solution, joining with oxygen and/or hydrogen. Containers which are normally collecting hydrogen and oxygen, will have different volumes of gases than in pure water electrolysis. f.e. electrolysis of iron made electrodes gives no oxygen on positive electrode - it's entirely immediately reacting with iron, and it's visible as yellow-reddish water. Electrode is literally disappearing. 1 hour is enough for me to wipe it out entirely. And water is totally opaque, yellow-reddish not transparent. But hydrogen container will be filled by gas - so we can easily calculate how much of oxygen reacted with iron.

After heating such solution, to get rid of entire water, there will remain small amount of powder. We can also calculate its mass.

Edited January 26, 2014 by Sensei