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Izzie0711
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An ion, RMM 14 g, initially moving at 200 ms-1 in a vacuum is subject to a constant acceleration of 400 ms-2 for 5 s. What force was required to give the ion this acceleration?Surely this is just F=ma however that is wrong and I don't know how to do it!
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BobbJo
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RMM has no unit.

1 mol of the ion weighs 0.014 kg
so 1 ion weighs 2.3 x 10^-26 kg
force is therefore 9.3 x 10^-24 N
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Kian Stevens
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(Original post by BobbJo)
RMM has no unit.

1 mol of the ion weighs 0.014 kg
so 1 ion weighs 2.3 x 10^-26 kg
force is therefore 9.3 x 10^-24 N
RMM has no unit...? It's g mol-1.
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BobbJo
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(Original post by Kian Stevens)
RMM has no unit...? It's g mol-1.
No. Molar mass has unit g/mol. RMM has no unit. Please do not confuse the OP.

RMM is defined as the ratio of the average mass of one molecule of an element or compound to one twelfth of the mass of an atom of carbon-12.
https://en.wikipedia.org/wiki/Molecular_mass
https://revisionscience.com/a2-level...e-formula-mass
https://www.dictionary.com/browse/re...molecular-mass
http://www.docbrown.info/page04/4_73calcs02rfm.htm
https://www.onlinemathlearning.com/molecular-mass.html
https://glossary.periodni.com/glossa...molecular+mass
https://dictionary.cambridge.org/dic...molecular-mass
https://www.quora.com/What-is-the-di...e-formula-mass
https://www.quora.com/How-do-I-teach...molecular-mass
https://www.thoughtco.com/molecular-...inition-606382
http://www.sky-web.net/science/calculate-RMM.htm
https://www.thefreedictionary.com/re...molecular+mass
https://study.com/academy/answer/how...-of-a-gas.html
http://www.rsc.org/learn-chemistry/r...id=CMP00005234
http://www.rsc.org/learn-chemistry/r...id=CMP00005011

RMM = mass of 1 molecule / 1/12 the mass of a C-12 atom
this quantity has no unit
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Izzie0711
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(Original post by BobbJo)
RMM has no unit.

1 mol of the ion weighs 0.014 kg
so 1 ion weighs 2.3 x 10^-26 kg
force is therefore 9.3 x 10^-24 N
This is right! Thank you I understand
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Kian Stevens
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My mistake. Confused RMM for Mr.
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BobbJo
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(Original post by Kian Stevens)
My mistake. Confused RMM for Mr.
RMM and Mr are the same thing. They are dimensionless quantities. The quantity called molar mass has a unit which is g/mol.

https://en.wikipedia.org/wiki/Molar_mass
"Molar mass is closely related to the relative molar mass (M
r) of a compound, to the older term formula weight (F.W.), and to the standard atomic masses of its constituent elements. However, it should be distinguished from the molecular mass (also known as molecular weight), which is the mass of one molecule (of any single isotopic composition) and is not directly related to the atomic mass, the mass of one atom (of any single isotope). The dalton, symbol Da, is also sometimes used as a unit of molar mass, especially in biochemistry, with the definition 1 Da = 1 g/mol, despite the fact that it is strictly a unit of mass (1 Da = 1 u = 1.660 538 921(73)×10−27 kg).[7][3]

Gram atomic mass is another term for the mass, in grams, of one mole of atoms of that element. "Gram atom" is a former term for a mole.

Molecular weight (M.W.) is an older term for what is now more correctly called the relative molar mass (M
r).[8] This is a dimensionless quantity (i.e., a pure number, without units) equal to the molar mass divided by the molar mass constant.[9]"
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Kian Stevens
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(Original post by BobbJo)
RMM and Mr are the same thing. They are dimensionless quantities. The quantity called molar mass has a unit which is g/mol.

https://en.wikipedia.org/wiki/Molar_mass
"Molar mass is closely related to the relative molar mass (M
r) of a compound, to the older term formula weight (F.W.), and to the standard atomic masses of its constituent elements. However, it should be distinguished from the molecular mass (also known as molecular weight), which is the mass of one molecule (of any single isotopic composition) and is not directly related to the atomic mass, the mass of one atom (of any single isotope). The dalton, symbol Da, is also sometimes used as a unit of molar mass, especially in biochemistry, with the definition 1 Da = 1 g/mol, despite the fact that it is strictly a unit of mass (1 Da = 1 u = 1.660 538 921(73)×10−27 kg).[7][3]

Gram atomic mass is another term for the mass, in grams, of one mole of atoms of that element. "Gram atom" is a former term for a mole.

Molecular weight (M.W.) is an older term for what is now more correctly called the relative molar mass (M
r).[8] This is a dimensionless quantity (i.e., a pure number, without units) equal to the molar mass divided by the molar mass constant.[9]"
You know, there are that many units for things which appear virtually the same, with the only difference being dimensionality, that it really is easy to confuse them all without the ability to check online or elsewhere.
There's so many different 'closely related but...' cases that it's difficult to differentiate. Personally, myself and many others I know simply use Mr, RMM etc. interchangeably, and have done for a long time.
So, again, apologies for not having the intricate detail at hand.
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