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April 20, 2014

Search: The half-life of Palladium-100 is 4 days. After 20 days a sample of Palladium-100 has been reduced to a mass of 3 mg

Number of results: 46,194

Calculus
The half-life of Palladium-100 is 4 days. After 12 days a sample of Palladium-100 has been reduced to a mass of 4 mg. What was the initial mass (in mg) of the sample? What is the mass 5 weeks after the start?
Thursday, February 18, 2010 at 11:49pm by <3

physics
If the physical half-life of sulfur-35 is 87.1 days, and the biologic half-life in the testicle is 632 days, what is its effective half-life in this organ? I know i have to find the time and then the half-life. But im having trouble finding the time A(t)=Ao x e ^ (-0.693) (t...
Thursday, October 24, 2013 at 9:58pm by Sarah

Math
normally I would have used \ amount = a(e^(kt)) where a is the initial amount, in your case it was 1 for 100% and k is some constant. but since they were talking about "half-life" I used 1/2 as the base for half-life questions, amount = a(1/2)^(t/half-life period) in your case...
Tuesday, October 11, 2011 at 7:58pm by Reiny

Chemistry
The metal palladium crystallizes in a face-centered cubic lattice with an edge length of 388.8 pm. What is the density of the palladium?
Monday, February 4, 2013 at 6:32pm by Sarah

science
Knowing the half-life of C-14 would allow you to take twice the half-life. From searching the Internet under "C-14 half life", I found that the half-life of Carbon 14 is 5730 years. This should help a little more. Thanks for asking.
Saturday, April 4, 2009 at 10:10pm by PsyDAG

chemistry
It depends upon what the half life is measured in. If the half life is 3.54 sec then k is in sec^-1. If half life is 4.5 min, then k is in min^-1. You may be asking the other way around (what unit for half life if k .....) but I think you gt the idea.
Monday, May 17, 2010 at 8:59pm by DrBob222

math
An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent. a)(a) What is the half-life of the element? half-life: b)How long will it take for a sample of 100 mg to decay to 51 mg? time needed:
Saturday, May 18, 2013 at 4:06am by Rachel

help huge test friday science
Half life is the time it takes for 1/2 the material to decay into something different. If you start with 100 marbles, (and they had a half life of 2 days), you would have 50 marbles at the end of 2 days, 1/2 of that or 25 at the end of 4 days, 12.5 at the end of 6 days, 6.25 ...
Friday, February 8, 2008 at 12:38am by drbob222

Half-Life
Uranium-238 decays to Lead-206. The half life of Uranium-238 is 4.5 billion years. If you have a 100 g sample. How much sample will you have after 2 half lifes?
Sunday, February 19, 2012 at 5:08pm by Noah

chemistry
You have k at one T (684) and you can calculate k at another T (427) with the Arrhenius equation. Then knowing it is first order, you can use ln(No/N) = kt. You can use any convenient number (such as 100) for No, use half that for N (50 if you use 100), plug in k at 427 (that'...
Friday, November 19, 2010 at 4:42pm by DrBob222

Chemistry
You will need k and you don't have information to get it. Look up the half life of C-14 which I think is in the neighborhood of 5800 years. Use the exact number when you find it. Then k = 0.693/t1/2 ln(No/N) = kt Substitute 100 for No. N = 25 k from the half life Solve for t.
Friday, March 22, 2013 at 2:03pm by DrBob222

College algebra
fraction remain = (1/2)^n where n is the number of half life half life = p/n where p is the period of decaying i.e. 47 years so, first find n (number of half life using the half life equation and then find the fraction remain. convert this fraction to % hope that helps
Sunday, May 12, 2013 at 4:20pm by bonjo

Chemistry
Uranium-238 has half life of 4.51 * 10^9 years Uranium-234 has half life of 2.48 * 10^5 years Thorium-230 has half life of 8.0 * 10^4 years Radium-226 has half life of 1.62 * 10^3 years Lead-210 has half life of 20.4 years. The rate constant for the decay of unstable nuclide X...
Tuesday, March 20, 2012 at 2:23pm by Harry

Chemistry
Mefenamic acid (Ponstan Forte) has a half life of 2 hours. Naproxen has a half life of 12 to 17 hours. Both are anti inflammatory drugs of apparently similar nature but could someone please explain the difference in half life? Thank you Mike
Thursday, August 13, 2009 at 4:31am by Mike

Science
That is three half-lives? first half life 1/2 remaining second half life 1/4 remaining third half life 1/8 remaining amountrmaing=0riginalamount (1/2)^(t/th) where t is time, th is halflife time.
Friday, April 17, 2009 at 1:29pm by bobpursley

life science
I cant grasp half life - the study guide question is how is half life dating used by scientists - I have 2 lines to write an answer
Thursday, February 7, 2008 at 11:53pm by claire

half-life
1. The half-life of a first-order reaction is 9.89 minutes. How many minutes will have elapsed after 27 half-lives? My answer is 267.03. 2. The half-life of a second-order reaction is 2.508 days. How many days will have elapsed after 8 half-lives? My answer is 5.330. Is this ...
Wednesday, February 7, 2007 at 5:43pm by Issac

chem
Can someone please help me with the following questions? 1:Suppose you were given an ancient wooden box. If you analyze the box for carbon-14 activity and find that it is 50% of that of a new piece of wood of the same size, how old is the wood in the box? 2:How old is an ...
Tuesday, January 2, 2007 at 8:15pm by Margaret

Chemistry
The half life of Ni-28 is six days. What fraction of a sample of this isotope will remain after 18 days? A 1/2 B 1/4 C 1/8 D 1/16 You can do this two or three ways. a. 18 days/6 days = 3 half lives; the sample will be 1/2 after 1 half life, 1/4 after two half lives, and 1/8 ...
Monday, July 19, 2010 at 8:17pm by DrBob222

chemistry
If half of it has decayed, then it has gone though one half life. What is the half life of C-14?
Saturday, November 26, 2011 at 11:42am by DrBob222

Chemistry
ln(No/N) = kt If we start with an arbitrary number, say 100, and 10% is used, that would leave 90 ln(100/90) = k(25sec) solve for k. You want the half life; therefore, substitute the k you find in the same equation but this time start with 100 and N = 50 (half is gone). Solve ...
Monday, May 3, 2010 at 9:44pm by DrBob222

chemistry
Do you have the half-life given in the problem or are you allowed to look it up? If so there is an easier way to set it up. To solve 2n = 16, take the log of both sides. log 2n = log 16 n*log 2 = log 16 n*0.301 = 1.2 etc. There is another way. Remember that half-life means the...
Monday, August 22, 2011 at 8:49pm by DrBob222

Math
Wow - that's a lot of work. each half-life diminishes the amount by half. 1/8 = 1/2 * 1/2 * 1/2 So, 150,000 years is 3 half-lives The half-life is thus 50,000 years.
Tuesday, August 20, 2013 at 9:23am by Steve

Chemistry
a)Calculate the lattice constant a in palladium (Pd).express your answer in angstroms. b) Calculate the distance (in angstroms) between adjacent (110) planes in palladium (Pd). Hint: use your work from part (a).
Thursday, November 22, 2012 at 8:32am by selly

linear/exponential
This question involves the half-life formula. In this exercise, we are to give a half-life for an exponentially decaying quantity. Need answer to the following: The half-life of a drug in the bloodstream is 4 hours. By what factor does the concentration of the drug decrease in...
Saturday, November 24, 2007 at 4:08pm by kayse

algebra 2
element x has a half life of 90 seconds. How much of a 100 gram sample of element x is left after half an hour
Tuesday, February 15, 2011 at 1:26am by frances

Half-Life
Use ln(No/N)=kt to determine the value of k. For example, start with 100 atoms/molecules/whatever in the reaction that is decomposing) so No = 100 and N = 100-42.6 = 57.4. t, or course, is 18.5 min. Then, knowing the value of k, use the same formula to calculate t. (No will be...
Sunday, June 21, 2009 at 7:02pm by DrBob222

Math/Radioactive Dating
First, let me correct a typo I made and it affects the answer but only slightly. k = 0.693/t1/2 = 0.693/1.25E9 = 5.54E-10 Then go through the x and 100-x bit I did earlier and x = 75 with 100-x = 25. Finally, ln(No/N) = kt ln(100/25) = 5.54E-10(t) ln(4) = 5.54E-10 t 1.386 = 5....
Saturday, February 19, 2011 at 5:56pm by DrBob222

Earth Science
Why is potassium-argon dating most applicable to dating very old rocks? potassiumís long half-life potassiumís short half-life argonís long half-life argonís short half-life
Thursday, February 21, 2013 at 12:09am by Anonymous

science
Half disappeared in one half-life. Half that remaining disappeared in the next half-life.
Saturday, April 4, 2009 at 10:10pm by bobpursley

Half-life
one half =1/2 left two half=1/4 three half=1/8 four half=1/15 one halflive=1/4 * 2hours=30 min
Monday, November 18, 2013 at 8:45am by bobpursley

college chem
No, I think you misunderstood. If the fifth life (I've never heard it used that way) is 20 s and that's the tim for 1/5 of it to be used, then start with No = 100 atoms/whatever it is so at the end of 20 s we will have 80 remaining. Then 1/5 x 80 = 16 so we have 80-16 - 64 ...
Sunday, February 21, 2010 at 10:31pm by DrBob222

math
Strictly speaking, a half-life is a number with dimensions of time, not an equation. It's value depends upon what the material is. If you meant to ask what is the amount N of material remaining After time t, in terms of half life T, then N(t)/No = (1/2)^(t/T) T is the half ...
Friday, February 15, 2008 at 12:47am by drwls

Chemistry(Please check)
Here are the equations for half life for order 0, order 1, and order 2. I didn't include order 3 because those reactions are not very common. zero order: half life = (Ao)/2ak 1st order: half life = ln 2/ak 2nd order: half life = 1/ak(Ao) note: a and k are constants.l (Ao) is ...
Monday, February 20, 2012 at 3:07pm by DrBob222

Chemistry
(a) Calculate the lattice constant a in palladium (Pd). Use only the information available in the class Periodic Table, and express your answer in angstroms. (b) Calculate the distance (in angstroms) between adjacent (110) planes in palladium (Pd). Hint: use your work from ...
Thursday, November 22, 2012 at 4:30am by c

Physics
yes. the half-life is how long it takes for the remaining amount to go down by 1/2. Since the half-life is given as 1 week, that means that each week there is only half as much at the end of the week as there was at the beginning of that week.
Thursday, August 29, 2013 at 2:13pm by Steve

Chemistry
Hydrogen gas dissolves in palladium with the hydrogen molecules going into the spaces between the metal ions. Determine the molarity, molality, and percent by mass of the H2:Pd solution (d=10.8g/cm)containing 0.94g hydrogen gas dissolved in 215 grams of palladium metal.
Friday, February 17, 2012 at 8:05pm by James

Chemistry
The half life of a material is the time it takes for exactly 1/2 of the material you started with to disintegrate into another material. In this case, the half life is 60 days. Therefore, 1/2 will be left after 60 days, 1/2 of the 1/2 (that is 1/4) will be left after 120 days...
Sunday, October 28, 2007 at 8:16pm by DrBob222

math
The general formula for a "half-life" problem is Value = original(1/2) ^(t/k) , where k is the half-life period. so what do you think?
Tuesday, November 1, 2011 at 6:53am by Reiny

Half-Life
If the half-life of a radionuclide is 1 month, is a sample of it completely decayed after 2 months?
Sunday, February 19, 2012 at 5:08pm by Dee

college chem
oh i see 1/5 times 80 is 16 so that is the fifth life of the rxn. for the half life usage should i take 50 seconds using the convenient number of 100 seconds?
Sunday, February 21, 2010 at 10:31pm by hymie

Second order half life
At 100 degrees C , a certain substance undergoes second-order decomposition with a half-life of 26 minutes. If the initial concentration of the substance is 3.9◊10−2M , what is the value of the rate constant at 100degrees C? So I put in (1560seconds) 1/2 = 1/ k (3.9◊10&#...
Tuesday, September 21, 2010 at 6:46pm by Sar

Chemistry
The half-life of iodine -131 is 16 days. If you start with 100 gram sample, how many half-lives have past when you have less than a gram left?
Sunday, October 28, 2007 at 8:28pm by Taylor

Chemistry
Palladium-107 undergoes ‚ decay (t1/2 = 6.5 x 105 yr) to form silver-107. How long will it take for 0.150 mol of silver-107 to form from 1.25 mol of palladium-107? help please...thank you :)
Tuesday, December 7, 2010 at 9:12am by Queen

Chemistry
A good rule of thumb is that it takes about 10 half lives for a material to decay to the point that it isn't dangerous (from the radiation). How would you like to live in a house that is built above a tank holding an isotope with a half life of 10 seconds? How about one with a...
Sunday, November 2, 2008 at 5:40pm by DrBob222

help huge test friday science
I cant grasp half life - the study guide question is how is half life dating used by scientists - I have 2 lines to write an answer
Friday, February 8, 2008 at 12:38am by claire

chemistry
A given reaction has an activation energy of 24.52 kJ/mol. At 25C the half-life is 4 minutes. At what temperature will the half-life be reduced to 20 seconds?
Saturday, April 9, 2011 at 4:04pm by Eddy

chemistry
If there are 80 milligrams of a radioactive element decays to 10 milligrams in 30 minutes then what is the elements half life in minutes? Ok i narrowed it down to either 10 or 30...but im rly confused so if u could help it wuld be grea 80 40 1 min 20 2 min 10 3min looks like ...
Sunday, March 4, 2007 at 7:19pm by jojo

Chemistry
Which radioactive sample would contain the greatest remaining mass of the radioactive isotope after 10 years? A. 2.0 grams of 198 Au B. 2.0 grams of 42 K C. 4.0 grams of 32 P D. 4.0 grams of 60 Co By the way the numbers next to the elements are their atomic masses. thanks ...
Saturday, March 3, 2007 at 8:50pm by Sanjay

chemistry
Pray tell what does caffeine have to do with tritium? For tritium, k = 0.693/t1/2 You will need to look up the half-life of tritium unless that is the "caffeine" half-life. Substitute k into the below equation. ln(No/N) = kt Nl = 125 N = 22 k = from above calculation. t = time...
Monday, April 11, 2011 at 7:07pm by DrBob222

math
You have just isolated a new radioactive element. If you can determine its half-life, you will win the Nobel Prize in physics. You purify a sample of 2 grams. One of your colleagues steals half of it, and eight days later you find that 0.1 gram of the radioactive material is ...
Sunday, October 21, 2012 at 2:34pm by Roseanne

Chemistry
All isotopes of technetium are radioactive, but they have widely varying half-lives. If an 800.0 g sample of technetium-99 decays to 100.0 g of technetium-99 in 639,000 y, what is its half life
Tuesday, December 11, 2012 at 11:06pm by Matthew

Alg2
If you can express the amount as y = a*2^(-t/n) then the half-life is n years. That is, as t increases by n, the amount is multiplied by 1/2 ae^-.0856t = a*2^(-t/n) divide by a and take logs -.0856t = -t/n ln 2 divide by t .0856 = ln2/n n = ln2/.0856 = .6931/.0856 = 8.1 So, ...
Thursday, December 8, 2011 at 7:37pm by Steve

chemistry
8mg to 0.25 mg means how many half lives. 1 half life = 4 mg remain 2 half lives = 2 mg remain 3 half lives = 1 mg remain 4 half lives = 0.5 mg remain 5 half lives = 0.25 mg remain. It takes 124 hours for a half life; therefore, it must take 124 x 5 for the 5 half lives.
Tuesday, October 12, 2010 at 8:29pm by DrBob222

Chemistry
Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 200mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals? 1- One half ...
Wednesday, September 18, 2013 at 7:12pm by Nadia

Chemistry
Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 200mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals? 1- One half ...
Thursday, September 19, 2013 at 4:26pm by Nadia

Chemistry
Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 200mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals? 1- One half ...
Thursday, September 19, 2013 at 7:54pm by Nadia

math
300 = 600e^-.00043t 1/2 = e^-.00043t -ln2 = -.00043t t = 1612 so, after 1612 years, half is gone. That's the half-life. Check: web search reveals a half-life of 1600 years or so.
Thursday, May 3, 2012 at 8:04pm by Steve

chemistry
Find the number of disintegrations per minute emitted by 1.1 mol of 232-Th in 1 min. The half-life of 232-Th is 1.4 x 1010 year I was able to do this with the following technique: 1.1 x 6.022 x10^23 =6.62x10^23 1.4x10^10=7.358x10^15 minutes I think then it is 6.62x10^23 x 7....
Thursday, August 2, 2012 at 1:18pm by Nancy

college
. S-35 (t1/2 = 87.4 d) is used in cancer research. The biological half-life in the human body is 90 days. What is the effective half-life of S-35?
Monday, May 3, 2010 at 9:51am by kurt

Physics
If T is the half life in days (1.6)/2.0 = (T/156)^(1/2) 0.8 = 0.08006 T^1/2 9.992 = T^1/2 T = 99.8 days The decay constant k is related to the half life by k = ln2/T
Tuesday, August 6, 2013 at 11:28pm by drwls

Half-life
After two hours, 1/16 of the initial amount of a radioactive isotope remains undecayed. What is the half-life of the isotope?
Monday, November 18, 2013 at 8:45am by Andrea

chemistry
The answer is "yes" but I am not sure what formula you are referring to. Are you expected to use the absorbance v. time graph to get the half-life? If so, ēSelect a point on the graph with a high value for absorbance, A. Read the time in minutes, T1. ēOn the absorbance axis, ...
Monday, May 17, 2010 at 9:14pm by GK

college chem
S-35 (t1/2 = 87.4 d) is used in cancer research. The biological half-life in the human body is 90 days. What is the effective half-life of S-35?
Monday, May 3, 2010 at 2:50pm by Anonymous

Chemistry 1046
Yes. See your post above. First calculate k using the half life, then use ln(No/N) = kt Use No = 1.1 mmol N = unknown k from half life t = 25.2
Tuesday, July 3, 2012 at 8:19am by DrBob222

Physics
Well, we know that half of it will change into another form in 5700 years, so if you start with .5 mg than in 5,700 years you would have half or .25 mg. 11,400 is another half life so half of .25 = .125 mg. 22,800 is two more half lives so half .125 twice.
Sunday, December 9, 2007 at 4:36pm by Rhonda

Physcis 30
Q1) If there are 100 radioactive atoms with a half-life of 30 seconds, how many radioactive atoms will remain after one half-life (30 seconds)? How many will remain after two half-lives (60 seconds)? Three half-lives? So basically, after 30 seconds it will be 50.After 60 sec. ...
Thursday, January 6, 2011 at 11:13am by Marium

Chemistry
.25=e^(-.692t/24) take the ln of each side, solve for t. You need to do that calc for practice. Now, the easy way with the numbers given. In the first half life, you have .50 left in the second half life, you have .25 left....which means .75 has been consumed. two half lives...
Wednesday, November 11, 2009 at 7:30am by bobpursley

half-life
Rn-222 has a half-life of 3.82 days. How long before only 1/16 of the original sample remains? Solution: recognize 1/16 as a fraction associated with 4 half-lives (from (1/2)4 = 1/16) 3.82 days x 4 = 15.3 days
Wednesday, February 7, 2007 at 5:43pm by Jeje

calculus
let the equation be A = 100 e^(kt) a) if amount = 95 95 = 100 e^(1k) .95 = e^k k = ln .95 so A = 100 e^(ln.95 t) when t = 50 A = 100 e^(50ln.95) = 7.69 g are left for half-life time, only 50 g of the original 100g would remain 50 = 100 e^(ln.95 t) .5 = e^(ln.95 t) ln.95t = ln....
Monday, March 19, 2012 at 12:43pm by Reiny

College Math
after one half-life, 1/2 of the material is gone. So, since more than half has gone, more than one half-life has passed.
Sunday, February 19, 2012 at 7:57pm by Steve

Math
Suppose a quantity is halvd every 18 years. use the approximate half-life formula to estimate its decay rate. is the half life equation y= 1/2^t1/2 2^1/2t= 1/y t 1/2= log2 (1/y) Where do I put 18 at?
Friday, December 4, 2009 at 4:05pm by Randi

Math - D.E.Q.
The half-life of a radioactive isotope is the amount of time it takes for a quantity of radioactive material to decay to one-half of its original amount. i) The half-life of Carbon 14 (C-14) is 5230 years. Determine the decay-rate parameter  for C − 14.
Tuesday, January 18, 2011 at 12:07pm by Justin

Math
What does the math symbols such as ^ and * mean? I still don't understand exactly what your trying to solve for. Am I trying to figure out the half-life of radioactive waste? Am I trying to figure out how many thousand years it takes in a half-life of radioactive waste? What ...
Tuesday, August 20, 2013 at 9:23am by Joy

Math
#1 70%=0.7 (because70%/100%=0.7) The half-life 1/2=0.5 Equation: 0.7=0.5^(t/5730) t=5730log0.7/log0.5=2949(years)
Sunday, November 21, 2010 at 9:08pm by Mi

math
.36 = (1/2)^(100/k) k = 67.84 so, the half-life is 67.84 days Makes sense, since the sample has decreased by a little more than 1/2 in 100 days. 51/100 = (1/2)^(t/67.84) t = 65.9 days
Saturday, May 18, 2013 at 4:06am by Steve

half-life of radioisotope
Just a word of caution on the wording and me being pedantic. The half life is referring to the original isotope so I like to see the answer referring to this. The mass of the sample may have changed only very slightly.
Friday, October 31, 2008 at 7:23pm by DrRuss

Chemistry
Let's start with 100 atoms of U238. Suppose x atoms of U238 decompose to Pb. Then there must be 100-x atoms U238 not yet decomposed. We know the ratio is 0.1462; therefore, (x/100-x) = 0.1462 and solve for x which is the amount of Pb formed and 100-x is the amount of U left. ...
Friday, May 6, 2011 at 10:18am by DrBob222

Alegbra
Andrew measures the amount of a very unstable substance to be 100 moles. The half-life of this substance is 3 days (after 3 days, half is gone). Write an exponential function that models this situation where y is the amount of substance and x is time in days. Thank you for ...
Tuesday, May 1, 2012 at 6:58pm by Jessica

chem
http://www.webelements.com/palladium/atoms.html
Thursday, January 13, 2011 at 5:30pm by DrBob222

Geology
If 1.0 half life passed, it would be 600 million years. If 0.1 half life passed, it would be 60 million years. Since 0.5 half life has passed, it is 300 million years old.
Thursday, April 15, 2010 at 3:42pm by e

Chem Class
The rate constant of a first-order process that has a half-life of 225 s is ?????? s-1. ok so i divided half life of 1st order= 0.693/K k i put 225 and i got 3.08 x 10^-3 is that right?
Monday, October 25, 2010 at 12:43pm by Laynie

half life
If the radiological half life of a material is 31 minutes, and you have 77 grams now, how much did you have 55 minutes ago?
Thursday, January 13, 2011 at 10:52am by julie

life science
Thank you for using the Jiskha Homework Help Forum. Although you don't reference this specifically, do you mean the game? http://en.wikipedia.org/wiki/Half-life
Thursday, February 7, 2008 at 11:53pm by SraJMcGin

Stats
Suppose X & Y are two independent stocks' returns with: E(X) = E(Y) =15% and V(X) = 144, V(Y) = 256 Problem 1. Buy half X and half Y, so w1 = w2 = 0.5 and Z = (X+Y)/2 Note: The answer says that the variance is 100 but I thought it would be 200. Since I would be adding half ...
Friday, September 14, 2012 at 6:07pm by Matt

Math/Radioactive Dating
How would I calculate the age of a rock only given the amount of each in grams and half-life? 40K decays to 40Ar. Half life of 40K is 1.25 billion years. 40K = 20 grams 40Ar= 5 grams I think the formula is Final Amount of 40K = Initial Amount of 40K * (1/2)^(time/half-life) If...
Saturday, February 19, 2011 at 2:12pm by Lena

Physical Science
Radioactive dating is limited by the half life of the element being used. C-14, with a half life of about 6,000 years, is not a good dating element for several hundred thousand years. With half of the material disappearing every 6,000 years or so there isn't enough to count ...
Tuesday, November 12, 2013 at 7:56pm by DrBob222

Chemistry
Half-life N2O5 dissolved in CCl4 decomposes to give N2O4 and O2. The reaction is first order with a half-life of 1234 seconds. How long will it take, in seconds, for the concentration of N2O5 to fall to 1.1% of its initial value?
Saturday, December 1, 2012 at 2:26am by Paul

Chemistry
The half-life (t1/2) of a first order reaction is 0.100 s. What is the rate constant? a. 6.93 s-1 b. 0.693 s-1 c. 0.0693 s-1 d. 0.144 s-1 e. 3.01 s-1
Friday, December 6, 2013 at 1:14am by Shines

algebra
Andrew measures they amount of a very unstable substance to be 100 moles. the half life of this substance is 3 days(after 3 days, half is gone). write an exponential function that models this situation where Y is the amount of substance and X is time in days. use your equation...
Friday, April 26, 2013 at 11:11pm by Anonymous

Half-Life
just do it in your head ... after 1 half-life you would have 50 g left after 2 half-lifes you would have 25 g left
Sunday, February 19, 2012 at 5:08pm by Reiny

Science
Radioactive substance decays so that after t years, the amount remaining, expressed as a percent of the original amount, is A(t)=100(1.6)^(-t). a) Determine the function Aí, which represent the rate of decay of the substance. b) what is the half-life for this substance? c) ...
Tuesday, March 6, 2012 at 11:03pm by jessica

chemistry
How do you find the half-life of an element? Please explain and show me how to do this. I know the answer is 14.3 days, but I don't know how to work it. thank you! the problem is: After 42 days, a 2.0-g sample of phosphous-32 contains only 0.25g of isotope. What is the half-...
Thursday, December 13, 2007 at 9:07pm by Ryan

calculus
The rate at which an amount of a radioactive substance decays is modeled by the differential equation dA/dt = kA, where A is the mass in grams, t is the time in years, and k is a constant. Answer the following. a) If a 100-gram sample of the radioactive substance decays to 95 ...
Monday, March 19, 2012 at 12:43pm by ronnieday

Physics
A half-life is how long it takes for a radioactive isotope to decay by half. At 2 PM, you will have .5 grams of the material. Each hour thereafter, divide the material by half to see how much remains.
Saturday, November 17, 2007 at 12:41pm by Michael

Science Half Lives
I am confused about how to claculate half lives. Can you explain. ( How much of a 400 gm sample od gold is left after 10.8 days if the half life is 2.7)
Tuesday, January 25, 2011 at 11:16pm by Krys

Chemistry
I assume the half life is 64 days and you want to reduce the radiation to 1/8 of its original value. k = 0.693/t1/2 and substitute this into the below equation. ln(No/N) = kt. No = 100 (an arbitrary number I picked). N = 12.5 (100/8) = 12.5 k from above. Solve for t in days.
Wednesday, April 27, 2011 at 8:22pm by DrBob222

Gen Chem
Neptunium-239 has a half-life of 2.35 days. How many days must elapse for a sample of 239-Np to decay to 1.00% of its original quantity? I got: close to 15 days. Is this right? I figured that about 1% of the original quantity would be roughly 6.5 Half lives, and since a half ...
Friday, March 28, 2008 at 5:34pm by Sarah H

Science- DrBob222
I'm confused about the "intersecting" part. The numbers mean this. The half life of Sr-90 is about 28 years so that's 28 years x 1 (1 half life) 50%left. 56 is 28 years x 2 or 2 half lives so 25% left. 84 is 28*3 = 3 half lives or 12.5% left. 112 is 28*4 = 4 half lives or 6.25...
Saturday, October 26, 2013 at 11:50pm by DrBob222

College Chemistry (DrBob222)
k = 0.693/t1/2 ln(No/N) = kt No = any convenient number but I would use 100 to represent 100%. Then if it decreases by 73% that leaves 27% so N = 27 k from above t = ? Solve for t in seconds if you use half life in seconds.
Wednesday, April 16, 2014 at 8:09pm by DrBob222

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