What is Molecular weight: Definition and 31 Discussions
The molecular mass (m) is the mass of a given molecule: it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quantity relative molecular mass, as defined by IUPAC, is the ratio of the mass of a molecule to the unified atomic mass unit (also known as the dalton) and is unitless. The molecular mass and relative molecular mass are distinct from but related to the molar mass. The molar mass is defined as the mass of a given substance divided by the amount of a substance and is expressed in g/mol. The molar mass is usually the more appropriate figure when dealing with macroscopic (weigh-able) quantities of a substance.
The definition of molecular weight is most authoritatively synonymous with molecular mass; however, in common practice, it is also highly variable as are the units used in conjunction with it. Many common preparatory sources use g/mol and effectively define it as a synonym of molar mass, while more authoritative sources use Da or u and align its definition more closely with the molecular mass. Even when the molecular weight is used with the units Da or u, it is frequently as a weighted average similar to the molar mass but with different units. In molecular biology, the weight of macromolecules is referred to as their molecular weight and is expressed in kDa, although the numerical value is often approximate and representative of an average.
The terms molecular mass, molecular weight, and molar mass are often used interchangeably in areas of science where distinguishing between them is unhelpful. In other areas of science, the distinction is crucial. The molecular mass is more commonly used when referring to the mass of a single or specific well-defined molecule and less commonly than molecular weight when referring to a weighted average of a sample. Prior to the 2019 redefinition of SI base units quantities expressed in daltons (Da or u) were by definition numerically equivalent to otherwise identical quantities expressed in the units g/mol and were thus strictly numerically interchangeable. After the 20 May 2019 redefinition of units, this relationship is only nearly equivalent.
The molecular mass of small to medium size molecules, measured by mass spectrometry, can be used to determine the composition of elements in the molecule. The molecular masses of macromolecules, such as proteins, can also be determined by mass spectrometry; however, methods based on viscosity and light-scattering are also used to determine molecular mass when crystallographic or mass spectrometric data are not available.
Hello everyone
I am trying to solve the following question from the book Analytical Chemistry 7th edition by Gard D. Christian - Page 164 Example 5.17
My problem is when I calculate the molecular weight of Pb(NO_3)_2 I get 331.2 g/mol but in the book they get 283.2 g/mol . Could you explain...
Found myself wondering about this recently, though I can't recall the context. When Mendeleev proposed the periodic table of elements, I believe that it was known that atomic weights of the known elements were multiples of hydrogen's atomic weight. Presumably also with substances like oxygen...
Homework Statement
Calculate the molecular weight of Al2(SO4)3.14.3H2O
Homework EquationsThe Attempt at a Solution
May i know how to do this ? Does it mean 14*3 = 42(H20) , where there re 84H , 42O atoms ?
Edit: thread moved from non HW forum.
I'm trying to calculate the unit molecular weight of polystyrene. I'm given the structure, and I have to count all the elements in the structure. To calculate the weight, I keep counting 8C & 7H. The correct answer is 8C +8H. I'm having a hard time...
Homework Statement
So for my homework assignment in 'Materials Science and Engineering', We were given the following problem.
1. Li and Ra both are both BCC metals. For this problem assume they form a complete solid solution (even though the very large difference in their atomic size tell us...
Homework Statement
Here is the question:
What weight of neutral red (molecular weight 289) must be dissolved in 1.00 ml to give a =40.0 µM (µmol l-1) solution? Give your answer in MICROGRAMS (µg).
Homework Equations
Not sure the only one I'm aware of is mole concentration (mol dm^-3) =...
A compound contains boron (40.3%), nitrogen (52.2%), and hydrogen (7.5%) - by mass. If 6.32g of this compound if dissolved in 100g of benzene, the solution freezes at 1.30 celcius. If the cryoscopic constant is 5.12 and freezing pt of benzene is 5.48, what is the molecular weight of compound...
Hi All,
I use commercial quantum dot from evident tech, and from the datasheet I can know its molecular weight (Mw), my question is, is this Mw also includes the organic ligand or only consider its core? what is the normal case?
thanks,
Yuliar
Hey there,
I am currently working on creating models in Abaqus of Wrist implants to see how they respond under different loading conditions. I have used Mimics to export orphan meshes of the wrist bones and also imported the wrist implant itself. My simulations seems to be running fine all...
[b]1. A 0.0097561 g quantity of an unknown gas occupies 0.2 L at 500 K and 2 atm. What is the Molecular Weight (MW) of the gas ?
[b]2. PV = nRT
[b]3. mw=0.0097561*0.082*500/2*0.2
mw=1
Homework Statement
The molecular weight of a monoprotic acid HX was to be determined. A sample of 15.126 grams of HX was dissolved in distilled water and the volume were brought to exactly 250mL in a volumetric flask. Several 50mL portions of this solution were titrated against NaOH solution...
Homework Statement
A compound with a molecular weight of 110.1 g that contained only C, H, and O was analyzed by combustion. the combustion of a 5.19 g sample of the compound resulted in the formation of 12.4 g of carbon dioxide and 2.55 g of water. What is the molecular formulas of this...
Homework Statement
I'm trying to figure out how to compute the average molecular weight of a gas mixture (nitrogen dioxide and dinitrogen tetroxide). I think I'm suppose to use this equation: M(mix)=X(NO2)M(NO2)+ X(N2O4)M(N2O4) , where I would just need to calculate the mole fractions and the...
Few quick questions, too lazy to look up this info my self:
1. Whats the max molecular weight for a single polymer strand of styrne (i.e what's the max number of styrenes you can link up).
2. Anyone know about the industrial process to produce ABS?
3. What is a good solvent for Styrene...
I need to calculate the mean square speed of molecules in an ideal gas. Mean square speed is equal to 3RT/M, where M is the molecular weight. But what units do I use for the molecular weight if I use 0.08206 L.atm/(mol.K) as R?
Thanks a lot.
Homework Statement
A gaseous hydrocarbon weighing 0.185g occupies a volume of 110.cm^3 at 26 celsius and 743mmHg. what is the molecular weight of this compound?
Homework Equations
PV=nRT
The Attempt at a Solution
i have no idea where to start ;(
Glucose (C6H12O6) is a monomer that can form naturally occurring polymers.
What would be the approximate molecular weight of a polymer made from 5 glucose monomers?
a) 810
b) 828
c) 882
d) 900
i said D, but my friend in convincing me its B :S
The specific heat at constant volume of an unknown solid is measured at high temperature to be 319.5Jkg-1K-1. Estimate its molecular weight.
Cv=3R
Attempt.
I used the above equation to get a mass of the solid to be 0.0128kg but I have no idea of what to do next!
is there any corrolation between thermal conductivity coefficient and molecular wieght Mw
according to the units [K] W/(m·K) it is independant of mass units (kg or g/mol etc)
in my question i am asked to show with a graph, but i have no idea what graph they are talking about
While both molecules have a very similar molecular weight, their boiling and melting points vary significantly. Explain the behavoir.
i have look everywhere to try and figure out why the bp and mp are different from mw but i just can't get anywhere!
Homework Statement
I did an experiment and found the weight of CaC(2)O(4)H(2)0 to be 31.4966 subtracted by the weight of a crucible which is 31.2612.
I put this for my weight of CaC204H20 (as I can't think of any other weight that it would be requested). I followed the next question...
WOuld someone be able to give us a hand for this question, I am stumped.
Polyethylene is a synthetic polymer or plastic with many uses. 2.06 g of a polyethylene sample was dissolved in enough benzene to make 100 mL of solution, and the osmotic pressure was found to be 1.86 torr at 25oC. What is...
Homework Statement
I just purified alkaline phosphatase, and my calculated molecular weight is 100000 g/mol, while literature value is 89000 g/mol. According to how others in my lab did calculations, my calculations are performed correctly, so I am left to explain why my purification is...
Hi Guys!
my question goes like this
a 5% solution of urea is isotonics with 0.877% of Solute A. Calculate the relative molecular weight of solute A.
now my dear friend, i know its a very simple question but unfortunately, just can't getting any interpretation. I know isotonics sol...
When it says; "Molecular Weight: daltons (g/M)" What does daltons mean and what does (g/M) stand for? Does g/M stand for g/mol or what?
How can they calculate Molecular Weight for nucleotides?
Thanks for any inputs.
What is the molecular weight of potassium phosphate buffer pH 6.8 and pH 6.4? I tried to find the answer but no luck. Please help calculate. Thank you. :bugeye:
Hi friends.
I am wondering about the next calculation.
Imagine there is a hole of some diameter, through which it is discharging a jet of an ideal gas of molecular weight W_1 (Kg/mol). Outside, there is an atmosphere at rest of molecular weight W_2 (Kg/mol). The external atmosphere has...
Chemical Separation Using Ranque-Hilsch Vortex
The full title for the post should be "Can molecules be separated in solution using a Ranque-Hilsch vortex?"
I am a chemist, and my conventions re: aerosols/liquids may be wrong. My interest is in a system that might enrich a soluble analyte in...