Questions tagged [units]
For questions about the definition and usage of units of measurement.
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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 to obtain the value of the gas constant R = 8.20574 × 10⁻² L atm K⁻¹ mol⁻¹
While reading a chemistry book, I saw a table of values of the gas constant for different units.
For example,
$$R=8.20574\times 10^{-2}\ \text{L}\cdot\text{atm}\cdot \text{K}^{-1}\cdot \text{mol}^{-1}\...
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What do the units of enthalpy kJ/mol represent?
Enthalpy is making me slightly confused.
Here $\Delta H$ refers to the change in enthalpy. Does this refer to the enthalpy change of reaction? Are they the same? It seems to be change in enthalpy, ...
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Units of mass on the atomic scale
what are the systems of recording atomic masses and their units?
I know that the nucleon number is the number of protons and neutrons
I also know that the mass number on the periodic table is the ...
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What is the correct unit of a RI detector used for HPLC analysis?
I analyze sugar compounds in soft drinks with HPLC using refractive index detection (RID) on Agilent 1260 Infinity Binary LC (System User Guide (PDF)). I am not sure which unit to put next to the $y$-...
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What is the unit of molar density?
I'm reading Unit operations of Chemical Engineering, 5th edition by Warren McCabe.
They defined the "molar density $\rho_{M}$" as $\ce{\rho_{M}=\frac{n}{V}}$. The parameters $n$ and $V$ are ...
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Masses of atoms and molecules [duplicate]
This is my understanding so far:
Average atomic mass is the mass of an element considering isotopes and is measured in atomic mass units. However relative atomic mass is the average mass of an atom ( ...
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Is it possible for me to derive Avogadro's number?
To my understanding the mole is the unit used to translate between mass on the atomic level and mass in the macro level, defined as the number of atoms in $12$ grams of Carbon-$12$, which apparently ...
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Definition of Avogadro's constant
I've read this excerpt from Wikipedia countless times, but I'm still confused:
The Avogadro number is the approximate number of nucleons (protons or neutrons) in one gram of ordinary matter.
Shouldn'...
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What is the correct method for converting a concentration given in ppm to molarity?
I need to convert a concentration of dissolved boric acid $(\ce{H_3BO_3})$ in water (at high temperature and pressure) from ppm to mol/L.
Concentration of boric acid: $c_{ppm}=1500\ \ce{ppm}$
Molar ...
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Is 1% m/m the same as 1% w/w?
Hydrocortisone cream seems to be sold as 1% w/w, but my cream is 1% m/m, which is confusing. Are they the same units or the same concentrations?
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How is the ln k term in the linearised Arrhenius equation acceptable?
In my syllabus we only study about rate laws under the topic "Rates of reactions", but as I was interested in it, I started to search about that topic. And then I found the Arrhenius equation
$$\ln k ...
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How to rewrite kinetic mass balance to get to proper SI units?
Suppose from kinetic mass balance I get the following differential equation of the molarity substances $A$,$B$, and $C$ in a reactor, with molar in- or outflow rate $\phi$, and rate constant $k$:
$$
\...
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How do you rewrite molarity to weight percentage or volume percentage?
Suppose I have a molar concentration $[C]$ in $mol/m^3$ in a continuous reactor, from which the differential equation is as follows:
$ \frac{\partial [C]}{\partial t} = k[A][B] + \phi C_{,in} - \phi ...
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Help with Forster distance conversion for FRET
For my project on Fluorescence, I'm trying to simplify the equation for the Forster distance (I obtained this from the Lakowicz book). To keep track, the units are in square brackets.
$$R_0 = \left(\...
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Convention for writing concentration units
1st part of my question:
Q) The concentration of an NaCl solution is 1M. Express this in percent wt. by vol. unit.
Ans:
$$\text{In %(w/v) unit}=\frac{58.5\pu g}{1000\pu{mL}}\times \frac{100}{100}=5.85\...
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Conversion from a PPB value to µg/m3 of Isobutylene
I have a quite simple problem, found a lot of information about it, but I am not sure anymore if I do my calculations right.
I own a sensor, which reports measurements in isobutylene units as PPB. So ...
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How to convert from dipole derivative to atomic units?
I need to convert dipole derivative output by Gaussian into atomic units. The dipole derivative is given in Gaussian in the weird units $(\mathrm{km/mol})^{1/2}$. I know that
$\pu{1 D^2/(Å^2amu)}$ = $\...
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How many mg caffeine is 1mM caffeine?
I am finding some articles about caffeine consumption confusing, because they test in units of mM instead of mg.
https://www.ncbi.nlm.nih.gov/m/pubmed/25342885/
Wikipedia says that the molar mass ...
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What is the dimension of molar mass?
I was told that the number of moles is ‘dimensionless’. Does this mean that the dimension of molar mass is simply mass and hence the unit g/mol can be expressed as equal or proportional to the dalton?
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Is 1 ppb equal to 1 μg/kg?
In an article I recently submitted, a reviewer asked that I provide a concentration in μg/kg instead of ppb (parts per billion), and mentions that the later is not correct. I am not a chemist, and I ...
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Can Rydberg constant be in joules?
In my textbook (Chemistry Part - I for Class XI published by NCERT), there is an equation for the energy of an electron in an energy state: $$E_n = -R_\mathrm H\left(\frac{1}{n^2}\right)$$ and there ...
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What is the name of the physical quantity that is given in kJ/g?
The chemical potential $\mu$ of a pure phase corresponds to the Gibbs free energy $G$ divided by the amount of substance $n$:
$${G\over n} = \mu,$$
so the units of $\mu$ are $\pu{kJ mol^-1}.$
What do ...
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How switching values of $R$, $K_p$ and $K_c$ does not alter the value of change in standard Gibbs energy? [duplicate]
$\Delta_\text r G=RT\ln \frac{Q}{K}$
If we switch $K_p$ from $K_c$, accordingly $Q_p$ will change to $Q_c$. Therefore, value of $\Delta_\text r G$ remains the same.
$ΔG^\circ=−RT\ln K=ΔH^\circ−TΔS^\...
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Units of collisional cross-section and reactive cross-section
I haven't been able to find the units of the reactive cross-section (σ* = Pσ) online but when I do a unit analysis from the equation:
$$ k = PσN_A √(\frac{8k_BT}{πμ}) e^{-E_a/RT}$$
then when plotting ...
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Is Avogadro's constant equal to 1? [closed]
The mole is defined to be exactly $\mathrm{mol}=6.02214076\cdot 10^{23}$ entities. Avogadro's constant is defined as $N_A=6.02214076\cdot 10^{23}\mathrm{mol}^{-1}$.
Then why is it not usual to write
$$...
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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 ...
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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 ...
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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?
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Why is the units of rate constant dependent on the order of the reaction?
In many textbooks, it is written that
For order (m + n), the rate constant, k has units of mol1−(m+n)·L(m+n)−1·s−1
However, by the Arrhenius equation, k can be expressed as
k = PZexp(-Ea/RT)
and ...
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Calculate concentration of 10 µM to ng/ml Cannabidol [closed]
I would like to calculate the concentration of 10 µM unit in vitro to blood plasma unit ng/ml?
What formula do I need to use?
Do I need to use molecular weight? In my case, it is 314,47 g/mol for ...
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Dealing with different units (psi) in ideal gas equation
My assignment is as follows:
A sample of air is trapped in a container at $\pu{16.2 psi}$. If the initial temperature is increased from $\pu{10 ^\circ C}$ to $\pu{32 ^\circ C}$, what is the final ...
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Is the amount of cubic inches in a cubic foot exact up to infinite significant figures?
I know we are supposed to use SI units and I know they are defined very well.
But does that mean that Imperial units of length/volume aren't exact? Don't they have infinite significant figures in the ...
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Thermochemistry: On Units of Enthalpy Change and Implicit Given of Initial Temperature of Calorimeter
I would like to ask two separate questions. But first, so that we are on the same page, the experiment used a constant-pressure calorimeter, and it is a neutralization reaction of 1M of HCl and 1M of ...
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Unit conversion of Molar Conductivity
I know this might be a silly question but I am confused with different answers of internet. My question is:
Molar conductivity is given as:
Molar conductivity = $\frac{\kappa}{M}$.
S.I. unit of :
$...
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