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### Topic: Atomic Structure  (Read 5259 times)

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#### Acidian

• Guest ##### Atomic Structure
« on: October 23, 2005, 10:52:36 AM »
I've amaged 9 questions of a worksheet but I cannot manage 2.

1.Describe one example of the use of radionuclides in investigating the mechanism of a reaction, and one of a use in industry.

For industry I would say regulating sheet thickness of aluminium foil. I'm finding it difficult to understand the first question.

2. The ratioof tritium 3H to hydrogen 1H is 1:1x10^19. If the half-life of tritium is 12.25 years, calculate the actual number of tritium atoms remaining in 10g of water after a period of 49 years.

I'm lost in the part of changing grams into atoms for some reason. The answer has to result to 4182 atoms (he gave us the answers but I cannot get to it).

Thank you in Advance

#### sdekivit

• Chemist
• Full Member
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• Mole Snacks: +32/-3
• Gender: • B.Sc Biomedical Sciences, Utrecht University ##### Re:Atomic Structure
« Reply #1 on: October 23, 2005, 11:10:25 AM »
this belongs to radiochemistry but since you know the ratio between H-3 and H-1 the problem should be easy. We start with 10 g H2O that you can convert to atoms by dividing by the molar mass and then multiply with the number of Avogadro.

--> then you know the amount of tritium in H2O due to the ratio and it's simply a matter of using the decay law.

--> my answer is 4178 atoms but it's depending on the numbers you take in your calculation.
« Last Edit: October 23, 2005, 11:16:53 AM by sdekivit »

#### Acidian

• Guest ##### Re:Atomic Structure
« Reply #2 on: October 23, 2005, 11:31:42 AM »
You mean this?

18g H2O = 2g H2
10g H2O = ?

(2x10)/18 = 1.11 (to 3s.f.)

No of atoms:
1.11 x (6.02214199 × 10^23) = 6.68 x 10^23

((((6.68 x 10^23/2)/2)/2)/2) = 4.175 x 10^22

1:1 x 10^19

(4.175 x 10^22) / 1 x 10^19 = 4175 atoms

P.S. Sorry for posting in the wrong part of the forum
« Last Edit: October 23, 2005, 11:39:15 AM by Acidian »