# Questions tagged [mole]

The mole is a standard amount of a substance A mole of a substance is a number of units (particles, atoms, molecules, ions, peas, hard candies, people, universes) equal to the number of atoms of carbon-12 in one gram of carbon-12, or an Avogadro's number of stuff. The mole allows us to relate real-word measurements to atomic scale phenomena.

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### What advantages does the mole have over counting large numbers using SI prefixes?

I'm trying to understand why chemists use the mole unit instead of just counting and using SI prfixes to simplify the big numbers with units such as zetta- or yotta-molecules (yotta=10^24). Here's ...
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### At what point does Avogadro's law not apply?

A mole of hydrogen gas takes up 22.4 L, but so does a larger molecule like $\ce{CO2}$. Methane ($\ce{CH4}$) is an even larger sized molecule, but a mole of it will still take up 22.4 L. I would assume ...
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### How to find the amount of moles given mass percentage data

A hydrated aluminium sulphate, $\ce{Al2(SO4)3.xH2O}$, contains 8.10% of aluminium by mass. Find the value of x. My attempt: (Assuming 100g sample) Calculate the amount of aluminium using the formula ...
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### Why are the mass ratios of O to KClO3 and O2 to KClO3 the same?

I just did a lab that involved heating KClO3 (with MnO2 as a catalyst) to decompose it into KCl and oxygen gas. That part is easy. What's throwing me is the % yield calculations. The theoretical ...
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### Why not an Avogadro's principle for solid matter?

Avogadro stated that for any ideal gas, 1 mole of particles will occupy a specific volume at a specific ratio of pressure and temperature. So why doesn't this apply to a liquid or solid?
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### Does 11.2 dm3 of nitrogen consist of 0.5 moles at STP?

Which of the following statements is true? $11.2~\mathrm{dm^{3}}$ of nitrogen at STP A: has a mass of $14\ \mathrm{g}$. B: consists of $0.5\ \mathrm{mol}$ atoms. My instinct was that the answer is ...
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### Comparing heat of hydrogenation per mole of butenes and 1,3-butadiene

The question asks us to select the compound with the smallest heat of hydrogenation per mole out of the following: a) 1-butene b) trans-2-butene c) cis-2-butene d) 1,3-butadiene Since all four ...
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### What is the correct value of the Avogadro constant? And how was it derived?

I found different values of Avogadro constant in different places. So what is the correct value? $\pu{6.0221367*10^{23}}$ or $\pu{6.02214129*10^{23}}$ or $\pu{6.0221415*10^{23}}$ or anything else?
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### CuCl2 dissolved in water

We dissolve $10\ \mathrm{g}$ of $\ce{CuCl2}$ in $0.1\ \mathrm{L}$ of water. Given that: $M(\ce{Cl})=35.5\ \mathrm{g/mol}$ $M(\ce{Cu})=63.5\ \mathrm{g/mol}$ How can one calculate the molar ...
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### Perplexing claim in Chang and Overby's “General Chemistry”

I'm reading the chapter on gases in Chang and Overby's book "General Chemistry: The Essential Concepts" [1, p. 145], and the following passage is causing me some confusion: The work of the Italian ...
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### Solute mole fraction for hydrated magnesium sulfate dissolved in water

Problem: 70 grams of pure, hydrated $\ce{MgSO_4}$ is dissolved in 90 grams of $\ce{H_2O}$. If the mole fraction of the solute is 0.039, find the molecular formula of the solute. My flawed attempt ...
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### Calculating the number of molecules remaining

This is the question in my text book: From $392\:\mathrm{mg}$ of $\ce{H2SO4}$, $1.204 \times 10^{21}$ molecules are removed. How many moles of $\ce{H2SO4}$ are left? What I tried doing: First I ...
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### Is the largest number of molecules in 36 g of water or 54 g of dinitrogen pentaoxide?

Recently my teacher asked us which of the following has the largest number of molecules? He gave us two options: $\pu{36 g}$ of $\ce{H2O}$ $\pu{54 g}$ of $\ce{N2O5}$ I'm stuck, because both of ...
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### Determine molecular weight of biomass based on ultimate analysis [duplicate]

The ultimate analysis (by weight percent) for beech wood is: $$\ce{C}=49.05\,\%,\; \ce{H}=5.83\,\%,\; \ce{O}=45\,\%,\; \ce{N}=0.12\,\%$$ Using the ultimate analysis values, the molar mass of each ...
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### Converting 26.62 NOx µg/L into mM (millimolars)?

I have to convert a whole lot of nutrient data : $\ce{NH_4}$, $\ce{PO_4}$ and $\ce{NO_x}$ data that is in µg/L into mM (millimolars). Could someone give me an example for 26.62 $\ce{NO_x}$ µg/L? or ...
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### Why are the masses of atoms less than the sum of their subatomic particles?

The mass of carbon-12 is $\pu{12 u}$ by definition. However, one carbon-12 atom comprises 6 neutrons (each weighing $\pu{1.0087 u}$), 6 protons (each weighing $\pu{1.0072 u}$), and 6 electrons (each ...
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### How to calculate a temperature change when the released heat of a process ist only partly absorbed by the medium?

Hi, I am able to do this question without the "80% of the heat released was absorbed by the water" part, and ended up getting 892.2g How, does "80% of the heat released was absorbed by the water" ...
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### Calculation of Solute Mole Fraction

Suppose we had an aqueous solution of density 0.984 g cm$^{-3}$, containing 100.0 g ethanol per liter. How would we compute the mole fraction of ethanol in this solution? My calculations so far ...
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### How to understand the concept of moles? [duplicate]

I have trouble relating to the mole concept. For example in a question like the following: How many moles of $\ce{K}$ are in 1 mole of $\ce{KOH}$? How is it that in 1 mol of $\ce{KOH}$ there ...
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### Why 6.023x10^23 is not written as 6023x10^20?

We know that 1 mole is equal to $6.023\times10^{23}$ atoms. But why it is not written as $6023\times10^{20}$ ?
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### What is the total concentration (in mol dm−3) of ions in each of the following solutions, assuming complete dissociation

$0.750\ \mathrm{mol\ dm^{-3}}$ solution of $\ce{K2CO3}$ (I believe is $2.25\ \mathrm{mol\ dm^{-3}}$) $0.355\ \mathrm{mol\ dm^{-3}}$ solution of $\ce{AlCl3}$ (I believe is $1.42\ \mathrm{mol\ dm^{-3}}$...
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### Why is O2 enough to form a mole of Oxygen? [closed]

I understand that this is the most basic knowledge of moles, however I'm still unsure - according to easy research, $\ce{O2}$ forms a mole of Oxygen. As a mole is $6.022*10^{23}$, exactly what on the ...
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### Calculating the volume of 1 mole of liquid water

I am doing some rough calculations to test my understanding of elementary chemistry. In what follows, I calculate the volume of one mole of liquid water at about $\pu{4 ^\circ C}$ and $\pu{1 atm}$: ...
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### Why was atomic mass scale changed from Oxygen - 16 to Carbon - 12?

Why was unified atomic mass scale introduced and why was Oxygen - 16 replaced by carbon - 12 for standardizing atomic scale?
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### How to find the volume of oxygen release by the decomposition if potassium chlorate?

In the reaction: $$\ce {2KClO3 -> 2KCl + 3O2}$$ What is the volume of oxygen released under NTP conditions when $36.75~\mathrm{g}$ of $\ce {KClO3}$ is heated? I tried to find the answer this ...
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### How do I calculate the mass percent in the original mixture?

I have the question: "A mixture of $\ce{KClO3}$ and $\ce{KCl}$ with a mass of 0.950g was heated to produce $\ce{O2}$. After heating, the mass of residue was 0.700g. Assuming all the $\ce{KClO3}$ ...
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### How report metal amounts as amount of their respective metal oxides?

I have performed an element analysis, and I I have calculated the amount of each metal in my sample, given in milligrams. Let's say I weighed in 10 mg of the powder. I want to see how much of that I ...
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### Understanding a concentration term

I am having a problem wrapping my mind around the idea that in $230\:\mathrm{mL}$ of $0.615\:\mathrm{M}$ $\ce{KCl}$ there is $0.141\:\mathrm{mol}$ of $\ce{Cl^-}$ ions. I guess I still do not ...
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### How many moles of aspartame are present in 4.00mg of aspartame? (3 sig figs) [closed]

This is a part of my online chemistry homework (mastering chemistry) I know how to do it but when I enter $\pu{1.36E-5}$ into the program, it says that it's incorrect and that the correct answer does ...
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### What is the mole fraction in mixture before combustion?

What is the mole fraction of $\ce{C2H6} / \ce{C3H8}$ in mixture, if both compounds reacted with $\ce{O2}$ in stoichiometric ratio? Mass of produced $\ce{CO2}$ is $1.819$ times larger than the mass of ...
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### The relationships between n , T , P , V for a gas?

The symbols : T : temperature // V : volume // P : pressure // n : number of mole what it is clearly known about the relationship between one another is : P is inversely proportional to V ( from ...
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### How can we say that one mole of a substance contains avogadro number of particles?

I just want to know, what was the procedure through which the value of one mole of a substance was considered as a an aggregate of $6.023\cdot10^{23}$ particles. Secondly, how do we calculate the ...
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### Why is the definition of the mole as it is?

I have asked my teacher, as she was introducing the concept of mole to us, why that number was chosen, instead of more convenient one. She told me that it came from the definition of the mole, that is ...
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### How to calculate the number of moles present in a litre of saturated solution?

The solubility product of a salt having same molecular formula as $\ce{Ca_3(PO_4)_2}$ is $1.08\cdot10^{-28}$. Then find the number of moles of ions present in the saturated solution. My approach: I ...
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### Calculating the mass in g of a molecule [closed]

If I have the amount of the molecule in moles, how do I calculate the mass of an individual molecule? For example, if the molecule was water?
From time to time I do little pro bono lessons for second grade in math, physics, and chemistry. Recently I came across this question. In a container is $2~\mathrm{mol}$ of $\ce{SO3}$ (sulfur ...