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What exactly is a mole?

The first thing to realize is that "mole" is not a mass unit. It is simply a quantity - a number - like dozen or gross or score. Just as a dozen eggs is 12 eggs, a mole of glucose is $6.02 \times 10^{...
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35 votes

Why was Avogadro's number chosen to be the value that it is?

Why was Avogadro's number chosen to be the value that it is? Your question implies that you already know that it was a choice rather than something derived from first principle. There are some ...
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25 votes
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Why is the definition of the mole as it is?

Why is the definition of the moles as it is? It is a rather arbitary definition that the mole is the number of atoms in 12g of carbon 12. This has not always been the definition. For example, prior ...
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24 votes
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What is the correct value of the Avogadro constant? And how was it derived?

Whenever you're looking for accurate fundamental physical constants, CODATA recommended values are the way to go. As of May 20, 2019, Avogadro's constant is now truly an exact value, with infinite ...
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19 votes
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What is the smallest molar volume?

Boron is a covalent solid with high melting point, like diamond (though not quite), and hence its crystals are hard to make. Unlike diamond crystals, they are not nice and probably wouldn't make a ...
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19 votes
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What is the intuition behind 'mol' as a unit 'symbol'

The symbol mol is due to Ostwald who was a very influential and respected physical chemist more than a century ago. In German, "mole" is "Mol". It is a shortform of Molekül. I ...
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18 votes
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Why are the masses of atoms less than the sum of their subatomic particles?

This is due to the mass-energy equivalence and a phenomenon called binding energy. Forming a nucleus releases energy because the nucleons are falling into a potential energy well. Due to Einstein's ...
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16 votes
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amu and g/mol relation

You are correct, but to make it a little more clear you can include the assumed "atom" in the denominator of amu: $$ \begin{align} m_{\ce{C}^{12}} &= \pu{12amu atom^-1} \\ \\ m_{\ce{C}^{12}} &...
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16 votes

What is the analogue of "molecule" for ionic compounds?

The term you are looking for is formula unit, I think. Wikipedia doesn't really describe it super well, but just to give an example, you could write the sentence $\pu{58.44 g}$ of $\ce{NaCl}$ ...
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16 votes

Avogadro's Number: 6.023 x 10^23 or 6.022 x 10^23?

Currently, the definition of Avogadro constant depends on the definition of the kilogram, and thus has an uncertainty. The recommended value[1][2] is $$N_\pu{A} = \pu{6.022140857(74) \cdot 10^{23} ...
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14 votes
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How to calculate valence factor (n-factor) for a element?

Hint : n-factor of a molecule/compound is defined as the change in oxidation state per molecule. You have correctly calculated the change of one carbon atom as 4. But how many carbon atoms are ...
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13 votes

How to explain the concept of mol and reactions involving mol quantities

The fundamental misunderstandings here are related to two concepts: Conservation (atoms are conserved, molecules are not) A mole is just a number (like the chemist's dozen) I would start with ...
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13 votes

Why was atomic mass scale changed from Oxygen - 16 to Carbon - 12?

The mass scale has changed over time, largely due to different isotopes of the "baseline." Not surprisingly, there's a good Wikipedia article on the matter. In the 20th century, until the 1960s ...
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13 votes

Why is Avagadro's number independent of substance?

It is the same reason that a dozen doesn't depend on whether you are counting grapes or elephants. That is how the mole is defined: it is a number, nothing else. The confusion, I suspect, is because ...
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13 votes

Why was Avogadro's number chosen to be the value that it is?

From the practical historical perspective chemists and physicists needed a number to use as a conversion factor from Daltons to grams to perform stoichiometric reactions. In the beginning, Dalton ...
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12 votes

Why 6.023x10^23 is not written as 6023x10^20?

Dissenter's answer is not quite right, since, strictly speaking, as defined there, the scientific notation will work for positive numbers only. Obviously, it can be easily fixed to work for negative ...
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12 votes
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Why are the mass ratios of O to KClO3 and O2 to KClO3 the same?

Your calculations are correct. The key is that you are measuring percentage by mass: the mass of oxygen in 2.062 g of $\mathrm{K}\mathrm{Cl}\mathrm{O}_3$ is the same whether it is considered the mass ...
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12 votes
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Is this definition of mole correct?

The mole is a base unit as specified in the Système international d’unités (SI) by the bureau international des poids et mesures. Its decisive definition is that published in French: La mole est ...
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11 votes
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What is the cheapest way to give someone 1 mol of gold?

According to Lamb, A. E., Anderson, C. W. N. & Haverkamp, R. G. (2001). The induced accumulation of gold in the plants Brassica juncea, Berkheya coddii and chicory. Chem New Zealand. 2011, 34-36.,...
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10 votes
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Finding out the number of atoms in the sun.

The problem is that you did not include units with your numbers. If you had, you would have easily seen that you are multiplying $m^3$ and $cm^{−3}$ and coming up with 1 instead of 1000000.
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10 votes
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How much sulphuric acid can be obtained from 5 kg of sulfur

$\ce{S6}$, $\ce{S8}$, $\ce{S12}$ – does it make a difference or is it just a trick to make the question more complicated than it is? What you know for sure is: $M(\ce{S}) = 32.065\ \mathrm{g}\cdot \...
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10 votes

What is the dimension of molar mass?

According to ISO ISO/IEC 80000 Quantities and units, BIPM The International System of Units (SI), IUPAC Quantities, Units and Symbols in Physical Chemistry (Green Book), NIST Guide for the Use of the ...
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9 votes
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Why is weight of 1 mole of substance equal to atomic/molecular mass in grams?

Why is weight of 1 mole of substance equal to atomic/molecular mass in grams? According to me, it happens because mole has been defined in such a way. Yes! That is correct. It is defined as the ...
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9 votes
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What is the mass of 1 atom of carbon?

Both approaches are correct. Avogadro's number is $6.02214129\times 10^{23}$ and represents the number of carbon-12 atoms in 12 grams of unbound carbon-12 in the ground electronic state. $12$...
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9 votes
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Why not an Avogadro's principle for solid matter?

Avogadro's law, which can be written as $V \propto n$, where $V$ is the volume of the gas and $n$ is the amount of substance of the gas (measured in moles), can be thought of as just another ...
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9 votes
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How to determine the equation for the reaction of europium with sulfuric acid based on experimental measurements?

Your equation isn't balanced; the oxidation state for europium is +3 and not +1; and europium sulfate does not exist in the solution you describe. From this link: Reaction of europium with acids ...
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9 votes

How to correctly write "7 apples" according to the international system of units (SI)

Mole is just a scale factor I find this description very intuitive: A mole is the amount of pure substance containing the same number of chemical units as there are atoms in exactly 12 grams of ...
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Atomic mass unit based on other atoms

Question: Which one is larger: an atomic mass unit based on the current standard or one based on the mass of a Be-9 atom? Answer It is easy enough to look up the weights of $\ce{^{12}C}$ (12....
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