## Converting mass to kilograms for de broglie

$\lambda=\frac{h}{p}$

romina_4C
Posts: 100
Joined: Thu Jul 11, 2019 12:17 am

### Converting mass to kilograms for de broglie

If a problem wants you to find the wavelength of an ion or an atom given the speed its traveling and no other information, how do you get the mass of the singular atom? If it was potassium for example, would you use the molar mass of potassium, change it to kilograms, and then divide by avogadros number?

Michael Du 1E
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Joined: Sun Sep 22, 2019 12:16 am

### Re: Converting mass to kilograms for de broglie

This is what I was wondering too, I was thinking about that process in which after converting to Kg, I would then convert from mols to atom with the Avogadro's number, but I am not too positive.

Brooke Yasuda 2J
Posts: 102
Joined: Sat Jul 20, 2019 12:17 am

### Re: Converting mass to kilograms for de broglie

if you are trying to find the mass of one atom of potassium to substitute into de broglie's equation, you would have 1 atom of K, multiply by the reciprocal of avogadro's number to get moles. From moles convert to grams, from grams convert to kilograms. From there substitute into de broglie's equation to find the wavelength.

Alexa Mugol 3I
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Joined: Sat Aug 17, 2019 12:17 am

### Re: Converting mass to kilograms for de broglie

That is correct. Since it's asking you for the wavelength of a single atom, you'd have to find the mass in kg of a single atom. It's also a good idea to make sure your units cancel out in your calculations and you're left with the units that you want.

WYacob_2C
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Joined: Sat Jul 20, 2019 12:16 am

### Re: Converting mass to kilograms for de broglie

You would need to find the mass. The molar mass is given in grams/mol, so first you would need to convert into atoms using (6.022 x10^23 atoms/mol). Then, convert grams into kilograms.

Anything with mass and velocity has a wavelength, so it will work out, you just need to use dimensional analysis to find the mass.

Matthew Tsai 2H
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Joined: Wed Sep 18, 2019 12:20 am

### Re: Converting mass to kilograms for de broglie

Yes, you would need to convert to kilograms because Planck's constant, h, uses kilograms.

Megan Jung 3A
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Joined: Thu Jul 11, 2019 12:17 am

### Re: Converting mass to kilograms for de broglie

Yes, you would need to convert into mass per atom by using the molar mass of potassium. Once you have molar mass (g/mol) divide by avagadro's number (1mol/6.022x10^23 atoms) and finally convert g to kg for SI unites (1kg/1000g).

Posts: 125
Joined: Sat Aug 17, 2019 12:17 am

### Re: Converting mass to kilograms for de broglie

romina_4C wrote:If a problem wants you to find the wavelength of an ion or an atom given the speed its traveling and no other information, how do you get the mass of the singular atom? If it was potassium for example, would you use the molar mass of potassium, change it to kilograms, and then divide by avogadros number?

Regarding units, you want to use: g (limiting reagent, molar mass), kg (whenever using Joules), m, J, s.

Yes, for the mass of a single atom of an element, you would take the molar mass (grams/mole), divide by Avagardo's Number this will yield (grams/atom). Then you would divide by 1000 to find (kg/atom). You have to convert to kg, because h in De Broglie has units (Js).