Tuesday
September 16, 2014

Homework Help: Chem

Posted by Tracy on Sunday, September 24, 2006 at 10:18am.

Okay so I have this assignment and I thought I knew how to do this but appearntly I am just lost. I know what the answer is suposed to be and I am deifantly no wheres near that. If you can sorta point me in the right direction that would be great. Thanks! The question is:

The isotope 99mTc, (t = 6.01 hours) is used in the diagnostic imaging of the heart and other organs. For diagnosing heart function, a particular dose has an activity of 3.09 x 108 disintegrations per second. Calculate the mass in grams of 99mTc required to produce this activity level. Use 98.91 amu as the atomic mass of 99mTc.

I thought you would use A=landaN and solve for N. And then you woudl get landa by using landa=0.693/(t1/2) and then just divide the amount for N by avagadros number to get moles, then change the moles to grams. Then chnage the mass they give you to grams and multiply the moles that you found for N by the gram amount and you would get the mass. I dont know if that makes sense but it does on my paper.


Use Activity= lambda*N Yes, lambda is .693/t1/2. Yes, you proceeded correctly, get moles, then grams.

N/avonumber * 98.91 = mass you are looking for.


But that doesnt work out cause thats what I did. But you still need to chnage to grams, and when you do it is WAYYYY wrong. lol I'm so confused


let me see your calcs.


Okay:
A= 3.09 X10^8 dis./s
t1/2= 6.01hrs

A=landaN
N=A/landa
Units are in seconds so gotta chnage the t1/2 to seconds
Landa=(0.693/6.01hrs)(1hr/60min)(1min/60s)
=0.00003203 /s

N=(3.09 x 10^8 dis/s)/(0.00003203 /s)
= 9.647205745 x 10^12 N

9.647205745 x 10^12N(1mol/6.022 x 10^23)
= 1.601993647 x 10^-11mol

98.91amu(1.66054 x 10^-24g /1amu)
= 1.642440114 x 10^-22g

= 1.601993647 x 10^-11mol (1.642440114 x 10^-22g /1mol)
=2.63 x 10^-33g

The answer is supposed to be 1.58 x10^-9g


Okay:
A= 3.09 X10^8 dis./s
t1/2= 6.01hrs

A=landaN
N=A/landa
Units are in seconds so gotta chnage the t1/2 to seconds
Landa=(0.693/6.01hrs)(1hr/60min)(1min/60s)
=0.00003203 /s

N=(3.09 x 10^8 dis/s)/(0.00003203 /s)
= 9.647205745 x 10^12 N

9.647205745 x 10^12N(1mol/6.022 x 10^23)
= 1.601993647 x 10^-11mol
<font=14>You are OK to here. Now just multiply 1.602 x 10^-11 x 98.91 = 1,58 x 10^-9 g</font=12>
98.91amu(1.66054 x 10^-24g /1amu)
= 1.642440114 x 10^-22g

= 1.601993647 x 10^-11mol (1.642440114 x 10^-22g /1mol)
=2.63 x 10^-33g

The answer is supposed to be 1.58 x10^-9g





N/avonumber * 98.91 = mass you are looking for.

But N= A/lambda= A*t1/2/.693

Now t1/2 has to be in seconds...

N= 3.09E8*6.01hr*3600sec/hr /.693
N= 9.65E12

mass= N/avonumber * 98.91
=9.65E12*98.91/6.02E23
=1.59 nanograms

check that.


Ohhh okay. so I think what I was doing wrong was just the fact that I was changing the AMU to grams, then dividing it and I forgot that amu can be considered grams at some points/


Okay thanks, I think I got it. I got 2.0E-9 so at least I know I'm in the right area. Thanks sooooo much.


I went through this independently and obtained 1.58 x 10^-9 g, also.

Answer this Question

First Name:
School Subject:
Answer:

Related Questions

Math - 11. In a survey of 260 dancers, 172 knew the ballroom dances, 145 knew ...
Physics - A copper wire with a criss section of 5 mm^2 and 2 km long has an ...
Pre Calculus - solving exponential equations with exponents on each side 5^x =4...
science - can energy be lost or does it transfer somewhere else? I thought ...
math - f(x)=x^3+4 f=1, f=-1 would the answer be 5 and 4? help Thought I knew ...
Fin 200 Intro to Finance - I have to make a statement of cash flow for the ...
Math- Corrections - (-9)-4w+7w=42 I thought I knew how to do this, but my ...
Healthcare - I have to do an assignment on Trends and Consumerism in Healthcare...
Advice...about chemistry degree Dr.Bob - Based on the question topic posted by ...
math - in a survey of 260 dancers: 172 knew the ballroom dances 145 knew latin ...

Search
Members