# Questions tagged [units]

For questions about the definition and usage of units of measurement.

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### Convert daltons (Da) to molar mass (g/mol) [duplicate]

This is probably a stupid question... In converting Da to molar mass (g/mol), Since 1 Da = 1 g/mol, is it logical that 64,776 Da = 64,776 g/mol or am I missing an intermediate calculation? Thank you!
1 vote
78k views

### Conversion of a value between g/gmol and lb/lbmol

I am doing some air emissions calculations and I really just have a bad feeling about my results. By definition, molecular weights are given in $\pu{g/gmol}$. For the substance I have, I was told by ...
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### Uncertainty when beaker goes by 50s

I am helping my daughter do her chemistry homework and am stumped by this one. I have a beaker that seems to count by 50s. That makes uncertainty calculations awkward. What is the “next unit down”? ...
7k views

### How to interpret parts-per notations? Is 1 ppb equal to 1 μg/kg?

In an article I recently submitted, a reviewer asked that I provide a concentration in μg/kg instead of ppb (parts per billion), and mentions that the later is not correct. I am not a chemist, and I ...
3k views

### What is the unit of Z effective?

Z effective is the net positive charge experienced by an electron. But what is the unit of this net charge: coulomb (C) or microcoulomb (μC), or something else?
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### Is the negative excess volume of ethanol/water the cause of my math error?

I have a binary mixture, say ethanol at $90\%wt$ ethanol, $10\%wt$ water. According to Perry's Chemical Engineers' Handbook 9th Ed., that mixture has a density of $0.81797g/cc$ (at $20^{\circ}C$). ...
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### How does the value of the equilibrium constant give information about the extent of reaction at equilibrium?

Pretty much everywhere I've read, the numerical value of the equilibrium constant gives you information about the relative concentrations of products and reactants in the equilibrium mixture; the ...
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### Units conversion of Henry coefficient in adsorption on solids [closed]

In a database of solid microporous materials I have the Henry coefficient in units of $\pu{mol kg^{-1} Pa^{-1}}.$ How to convert to $\pu{Pa^{-1}}?$ I tried to multiply by the molar mass of the sorbate ...
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### How much is 1 mμg?

So I stumbled on a research paper by Okuda and Takedatsu [1] that uses mμg as a symbol for the mass unit. I couldn't find anything about this measure unit anywhere except a recommendation not to use ...
1 vote
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### Find the displacement of mercury in a vertical tube

So we have a 1m tube sealed at both ends. It is initially horizontally placed and the middle 0.1m contains mercury and the two ends contain air. Now the tube is turned vertical, we have to find the ...
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### Will Avogadro's number change if definition of atomic mass unit is changed?

I know that the relation between atomic mass unit and Avogadro's number is a reciprocal relation. My question is if the definition of atomic mass unit is changed, suppose instead of 1/12th mass of ...
1 vote
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### Why isn't entropy dimensionless?

The usual units are J/K, however the only reason temperature has different units than energy is because we didn't used to know temperature was just the average kinetic energy of atoms/molecules. ...
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### Why does osmolarity take into account both penetrating and non-penetrating solutes?

According to Wikipedia: … osmolarity takes into account the total concentration of penetrating solutes and non-penetrating solutes, whereas tonicity takes into account the total concentration of non-...
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### Regarding units of water potential and chemical potential

If water potential is nothing but the chemical potential of a given solution, then why do their units differ? If the unit for the latter is taken as 'Energy per molecule' (which makes sense to me ...
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### Would 10.0 mL of water at 10 °C have the same mass as 10.0 mL of water at 25 °C? [closed]

I am reading a book and it gives the following answer: No, the density of water changes with temperature. 10.0 mL of water at 10 °C would have a higher mass than 10.0 mL of water at 25 °C because the ...
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### How to convert ppm to g/m3?

I'm not very comfortable with chemistry and I need to convert $\ce{CH4}$ concentration values in $\pu{ppm}$ to $\pu{g/m3}$. Is that possible? I've already researched a bit and realised that for water ...
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### Why are these two methods of converting from ppm to g/m3 equivalent?

I've found two methods to convert from $ppm$ to $g/m^3$. They both appear to give equivalent results, but I don't understand why. Can anyone join the dots for me and explain why they are equivalent ...
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### What is the 'electronic energy', in units of 'negative' hartrees, of a molecule?

On a NIST (National Institute for Standards and Technology) page on the molecular details of water and it's various isotopologues, I came across this: Electronic energy: -76.4089547246 hartree There ...
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### Why do the units of rate constants change, and what does that physically mean?

Just to be clear, I do understand that the units of the rate constant k is selected to make the equation dimensionally consistent. That is not what I am asking. It should be the case that k 'means' ...
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### What is the difference in mosM and mOsm units, if there is any at all?

I'm reading Agre's paper on aquaporins [1] and he uses a unit called "mosM" throughout the paper, for example: … ocytes were transferred from 200 mosM to 70 mosM modified Barth's buffer. I ...
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### When multiple sources give the content of an ingredient my an unqualified percentage, can I safely assume this is by weight? Or; it's not a wart

I am trying to make a simple scented shampoo and body soap for my own use and for Christmas gifts. I statr with a base of 32 oz – (a bit under a kg) of a mild commercial castille soap (Dr. Bronner’s ...
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### Are the units of mole of oxygen molecules the same with the units of mole of nitrogen molecules?

Suppose we have in a box $3 \,{\rm mol}$ $\ce{O}$ and $3 \,{\rm mol}$ $\ce{N}$. Is the addition of these two quantities meaningfull? We do it all the time when we want to find the molar fraction. I ...
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### Is it accurate to describe these radiation measurement units in terms of where-it's-measured and relationship-to-time?

I'm reading about measuring radiation and trying to come up with a more intuitive retelling for an audience familiar with math but not necessarily chemistry or any physical science. Is any or all of ...
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### What is the intuition behind 'mol' as a unit 'symbol'

Why are moles written with 'mol' as opposed to something which is easier to write with one character, or even two?