## Test #2: Q5 [ENDORSED]

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

Gabi Landes 1-H
Posts: 31
Joined: Thu Feb 22, 2018 3:00 am

### Test #2: Q5

I got this question wrong on the test -- I just want to make sure I am on the right track now. Thanks!

Q5. Electrical signals within the body are transmitted by the movement of sodium ions in and out of neurons. When pain signals are sent, the local velocity of a sodium ion is assumed to be 1.34 m/s. What is the de Broglie wavelength of one ion of sodium?

Given: v=1.34 m*s-1 m=22.989 amu

$\lambda =h/p$
$\lambda$=(6.62608x10-34 J*s)/(22.989 g/mol-1)(1.34 m*s-1)x(6.02214x23 mol-1)x(1000 g/1 kg)
$\lambda$= 1.29x10-8 m

tmehrazar
Posts: 39
Joined: Fri Apr 06, 2018 11:04 am

### Re: Test #2: Q5  [ENDORSED]

looks right to me!

yazminedesan1F
Posts: 40
Joined: Thu Feb 15, 2018 3:00 am

### Re: Test #2: Q5

How were you able to see the quiz earlier than discussion?

Johanna Caprietta 1E
Posts: 30
Joined: Fri Apr 06, 2018 11:02 am

### Re: Test #2: Q5

I was confused with this question as well. It asks for the wavelenth of a sodum ion, does the mean we have to use Avagadro's number to convert from grams to moles or can we solve for the problem by just leaving it as grams.

Chem_Mod
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### Re: Test #2: Q5

How were you able to see the quiz earlier than discussion?

Some TAs were able to return the exam to his/her discussion sections after the Friday lecture already. You will receive your test back in discussion unless your TA decides to return it early.

Kuldeep Gill 1H
Posts: 44
Joined: Fri Apr 06, 2018 11:02 am
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### Re: Test #2: Q5

Johanna Caprietta 1E wrote:I was confused with this question as well. It asks for the wavelength of a sodium ion, does the mean we have to use Avogadro's number to convert from grams to moles or can we solve for the problem by just leaving it as grams.

Yes so the way you would go about this is to find the mass of one sodium ion you do this by taking the molar mass dividing by 1000 to get kg/mol then dividing by Avogadro's number to get the mass of one sodium ion then you just use the de Broglie equation by plugging in mass in kg which you just found and velocity which is given and using planks constant to divide by all of that to find the wavelength! Hope that helps!!

Gabi Landes 1-H
Posts: 31
Joined: Thu Feb 22, 2018 3:00 am

### Re: Test #2: Q5

yazminedesan1F wrote:How were you able to see the quiz earlier than discussion?

My TA passed our quizzes out after class on Friday!

Paywand Baghal
Posts: 32
Joined: Fri Apr 06, 2018 11:01 am

### Re: Test #2: Q5

Kuldeep Gill 1H wrote:
Johanna Caprietta 1E wrote:I was confused with this question as well. It asks for the wavelength of a sodium ion, does the mean we have to use Avogadro's number to convert from grams to moles or can we solve for the problem by just leaving it as grams.

Yes so the way you would go about this is to find the mass of one sodium ion you do this by taking the molar mass dividing by 1000 to get kg/mol then dividing by Avogadro's number to get the mass of one sodium ion then you just use the de Broglie equation by plugging in mass in kg which you just found and velocity which is given and using planks constant to divide by all of that to find the wavelength! Hope that helps!!

I may be wrong but I thought you would need it to be in g/mol to use Avogadro's number, not change it to kg?

Kuldeep Gill 1H
Posts: 44
Joined: Fri Apr 06, 2018 11:02 am
Been upvoted: 1 time

### Re: Test #2: Q5

Paywand Baghal wrote:
Kuldeep Gill 1H wrote:
Johanna Caprietta 1E wrote:I was confused with this question as well. It asks for the wavelength of a sodium ion, does the mean we have to use Avogadro's number to convert from grams to moles or can we solve for the problem by just leaving it as grams.

Yes so the way you would go about this is to find the mass of one sodium ion you do this by taking the molar mass dividing by 1000 to get kg/mol then dividing by Avogadro's number to get the mass of one sodium ion then you just use the de Broglie equation by plugging in mass in kg which you just found and velocity which is given and using planks constant to divide by all of that to find the wavelength! Hope that helps!!

I may be wrong but I thought you would need it to be in g/mol to use Avogadro's number, not change it to kg?

Actually I initially agreed with you but after thinking about it for a while I think you could do it either way since we are cancelling out moles in the end it would either be kg or g so as long as moles can be cancelled out the fact that it is kg or g should not matter you would just have to do the conversion to kg after cancelling out moles the way you suggested and I just did the conversion from g to kg before I cancelled out moles!

105012653 1F
Posts: 30
Joined: Fri Apr 06, 2018 11:02 am

### Re: Test #2: Q5

this makes so much more sense now... thanks!