48 votes
Accepted

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

You are correct suggesting that 1 μg/kg implies 1 ppb, however the reverse is not true. For instance, 1 ppb can also be 1 nmol/mol, and the reader will never have a chance to deduce which one is it ...
andselisk's user avatar
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43 votes
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How much is 1 mμg?

Looks like in 1966 there were still residues of double prefix notation in use. Here's an entry from Russ Rowlett's compilation of units on ibiblio.org (Rowlett): millimicro- (mμ-) an obsolete metric ...
z1273's user avatar
  • 1,379
39 votes

Why do we still need to know about the Rankine temperature scale?

Rankine is commonly used in the aerospace industry in the United States. Rankine is to Fahrenheit what Kelvin is for Celsius. So when people in the United States were creating programs and using ...
Rick's user avatar
  • 491
21 votes
Accepted

What is a Herzberg?

Herzberg filtration speed: The time taken to filter $\pu{100 mL}$ water at $\pu{20 ^\circ C}$ through a filter area of $\pu{10 cm2}$ at a constant pressure of $\pu{5 cm}$ water column (Thomas ...
Mathew Mahindaratne's user avatar
19 votes

Where does the label ‘Dq’ to denote the field split in coordination compounds come from?

I will expand my previous comment into an answer. In the $O_h$ case the metal ion is surrounded by $6$ ligand ions, each with charge $q=-Ze$ located at $\langle\pm a,0,0\rangle$, $\langle0, \pm a,0\...
user5713492's user avatar
  • 1,058
19 votes
Accepted

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 ...
AChem's user avatar
  • 40.2k
18 votes

Why do we still need to know about the Rankine temperature scale?

Most of us in the world use the Celsius scale to measure temperature for day-to-day purposes. The Kelvin scale has been designed in such a way, it is not only an absolute temperature scale, but also 1°...
Pritt says Reinstate Monica's user avatar
17 votes
Accepted

What is the unit of Z effective?

This is an example of terminology which should be taken with a grain of salt. The term "effective nuclear charge" is often casually symbolized with $Z_\mathrm{eff}.$ This is a universally ...
andselisk's user avatar
  • 37.7k
16 votes
Accepted

What is the correct unit for the equilibrium constant?

Andselisk correctly identified the law of dilution and the name Ostwald is often connected with it. $$K_\text{dissociation} = \frac{\alpha^2}{1-\alpha}\cdot c$$ However, the degree of dissociation is $...
Martin - マーチン's user avatar
14 votes
Accepted

Where does the label ‘Dq’ to denote the field split in coordination compounds come from?

I currently happen to have the book by Figgis that Max mentioned. Chapter 2 is devoted to a mathematical formulation of crystal field theory, which I did not bother reading in detail because I do not ...
orthocresol's user avatar
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14 votes
Accepted

Can Rydberg constant be in joules?

Authors may be sloppy about notation in this matter. I recommend considering $R_\ce{H} \approx \pu{10973 cm-1}$ and $Ry \approx \pu{2.18e-18 J}$, noting $Ry = hc \cdot R_\ce{H}$. Units of wavenumbers $...
electronpusher's user avatar
13 votes

Where does the label ‘Dq’ to denote the field split in coordination compounds come from?

A more high-level answer this time. In this approach we first find out the form of the term in the potential that will split the $d$ orbitals. Recall that the character of a proper rotation by angle $\...
user5713492's user avatar
  • 1,058
12 votes

Why do we still need to know about the Rankine temperature scale?

I am currently studying mechanical engineering in the US, and I have used Rankine. It is used similarly to Kelvin. For example, in my thermodynamics class we used it to analyze various heat engines. ...
BillThePlatypus's user avatar
11 votes
Accepted

Is zero-point vibrational energy an intensive or extensive property?

Mathematically, an extensive property $f$ is one for which $f(\lambda x,\lambda y,z) = \lambda f(x,y,z)$ for extensive variables $x$, $y$, and intensive variable $z$. For example, the Helmholtz free ...
a-cyclohexane-molecule's user avatar
11 votes

Which unit should I use for m/z?

TL;DR: According to current IUPAC recommendations, $m/z$ is an abbreviation for a dimensionless quantity. Use of thompson unit is indeed currently discouraged. There is an overview provided in ...
andselisk's user avatar
  • 37.7k
11 votes
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Can someone intuitively explain the reason for the units of entropy (J/K )?

The units of of energy over temperature (e.g. J/K) used for entropy in the thermodynamic definition follow from a historical association with heat transfer under temperature gradients, in other words, ...
Buck Thorn's user avatar
  • 21.7k
11 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 ...
Loong's user avatar
  • 4,813
10 votes

Can Rydberg constant be in joules?

Rydberg constant $R_∞$ is usually given in reciprocal length units historically and because it's determined from hydrogen and deuterium transition frequencies [1]. Current value (in $\pu{m-1}$) is ...
andselisk's user avatar
  • 37.7k
9 votes
Accepted

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

A gram-mole ($\pu{gmol}$),often just called a mole ($\pu{mol}$), is the amount of a material whose mass in grams equal to the numerical value of the atomic or formula mass. For example, a gram-mole of ...
Oscar Lanzi's user avatar
  • 57.1k
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 ...
Dennis's user avatar
  • 91
9 votes
Accepted

Is it possible for me to derive Avogadro's number?

To determine Avogadro's number you have to measure the same unit at the atomic and macroscopic scales. This was first achieved by Millikan who measured the charge of an electron. The charge of one ...
Raoul Kessels's user avatar
9 votes
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How to determine omitted units in a publication

These are degrees Celsius. To prove that, you could search JACS for the publications of the same year/issue for the temperature-related physical constants such as melting point: Douglas et al. [1] ...
andselisk's user avatar
  • 37.7k
9 votes
Accepted

Uncertainty when beaker goes by 50s

A real beaker says "approximate volume". So the volume is approximately between 100 mL and 150 mL. So maybe 125 mL with an uncertainty of 25 mL. Your daughter would know best because she ...
Karsten's user avatar
  • 40.2k
8 votes

What term should I use when I am quantifying the amount of matter, mass or weight?

Because of the reasoning provided by you, i.e. mass is universal, and weight is the product of mass and magnitude of the local gravitational acceleration, I suggest to stay at mass. (A purist's view, ...
Buttonwood's user avatar
  • 29.8k
8 votes

What is the correct unit for the equilibrium constant?

By definition, the equilibrium constant has no units, as we're supposed to be using active masses instead of the molarity/ concentrations of the respective substances. Active mass is a unit-less ...
Abhigyan's user avatar
  • 1,667
8 votes

In biochemistry, when do rate constant units matter in calculating free energy changes?

$K$ should be a unitless value. Otherwise, you'd get a nonsensical unit when you try to take the log of the unit. Each component of the product $K$ is usually an activity, which is frequently similar ...
Zhe's user avatar
  • 17.4k

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