# Fluorine-20 has a half-life of 11.0 s. If a sample initially contains 49.0 μg of this isotope, how much remains after 66.0 s ?

33,042 results
1. ## science

The half-life of carbon 14 is 5730 years. if a 1 g sample of old carbon is 1/8 as radioactive as 1 g of a current sample, then the age of the old sample is about ___________years. 22,900 17,200 11,500 716

2. ## 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

3. ## Chemistry

Nitrogen dioxide decomposes at 300°C via a second-order process to produce nitrogen 14) monoxide and oxygen according to the following chemical equation. 2 NO2(g) → 2 NO(g) + O2(g). A sample of NO2(g) is initially placed in a 2.50-L reaction vessel at

4. ## Chemistry

Upon decomposition, one sample of magnesium fluoride produced 1.65kg of magnesium and 2.58kg of fluorine. A second sample produced 1.38kg of magnesium. How much fluorine (in grams) did the second sample produce?

5. ## chemistry

How long will it take for 25% of the C-14 atoms in a sample of C-14 to decay? The half-life for the radioactive decay of C-14 is 5730 years. If a sample of C-14 initially contains 1.1 mmol of C-14 , how many millimoles will be left after 2275 years?

6. ## chemistry

Fluorine-20 has a half-life of 11.0 s. If a sample initially contains 49.0 μg of this isotope, how much remains after 66.0 s ?

7. ## Chemistry

Gallium65, a radioactive isotope of gallium, decays by first order-kinetics. The half-life of this isotope is 15.2 min. How long would it take for 7/8 of a sample of this isotope to decay? 15.2 min 30.4 min 45.6 min 48.0 min I'm not sure how to do this. I

8. ## chemistry

There are 5g of 131I left after 40.35 days. How many grams were in the original sample if its half-life is 8.07 days? What is the half life of a radioisotope if you started with 1 gram and 0.250 grams is left after 6 days? im not looking for a free answer,

9. ## Science

The half life of an element x is 5days. If we have 5g of x initially, what is the mass of x after

10. ## Physics

Gold-198 with a half life of 2.6 days is used to diagnose and treat liver disease. Write a half life decay equation that relates the mass of au-198 remaining to time in days. What percentage of a sample of Au-198 would reamin after 1 day, 1 week? Given the

11. ## physics

The half life of a radioactive sample is 6.93 days.after how many days will only one -tenth of the sample be left behind?

12. ## math

An element has a half-life of 30 years. If 1.0 mg of this element decays over a period of 90 years, how many mg of this element would remain? Begin amount is 1.0 elapsed time is 90y half life 30 years n=9/30 n=3 90/2^2 90/8 = 11.25mg thinking it's wrong

13. ## 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

14. ## College Algebra

Use a calculator to help solve the problem. One isotope of holmium, 162Ho, has a half life of 22 minutes. The half-life of a second isotope, 164Ho, is 37 minutes. Starting with a sample containing equal amounts, find the ratio of the amounts of 162Ho to

15. ## 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

16. ## math

Iodine-131 is a radioactive isotope used in the treatment of thyroid conditions. It has a half-life of 8 days. Half-life is the amount of time it takes for half of the substance to decay (or disappear). If a patient is given 20 mg of iodine-131, how much

17. ## college algebra

One isotope of holmium, 162Ho, has a half life of 22 minutes. The half-life of a second isotope, 164Ho, is 37 minutes. Starting with a sample containing equal amounts, find the ratio of the amounts of 162Ho to 164Ho after one hour. Rounded to three decimal

18. ## 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

19. ## Chemistry

The half life of U238 is 4.5 x 10^9 yr. A sample of rock of 1.6 g produces 29 dis/sec. Assuming all radioactivity is due to U238 find percent by mass of U 238. I have tried ln(t)/ln(0)= -kt and still cannot get the answer What I get is A) 4.5x10^9

20. ## 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

21. ## Engineering Math

An unknown radioactive element decays into non-radioactive substances. In 120 days the radioactivity of a sample decreases by 59 percent. What is the half life of the element? How long will it take for a sample of 100 mg to decay to 77 mg? The answer is

22. ## chemistry

the half-life of polonium-218 is 3.0 minutes. what percentage of the original sample remains after 4 half-lives?

23. ## Chem 2

The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentration. a) How long will it take for 10% of the U-238 atoms in a sample of U- 238 to decay? b)If a sample of U-238 initially contained 1.9×1018

24. ## chem

Cesium-137 has a half life of 30.0 years. If initially there are 8.0 kg of cesium-137 present in a sample, how many kg will remain after 60.0 years?

25. ## chemistry

a radioactive material is undergoing nuclear decay. After 40 minutes, 25% of the sample remains. What is the half-life of the sample

26. ## Ap chemistry

a sample of radioactive iodine (half life=3 days) originally weighed 10 g, but now weighs 0.625 g. How old is the sample?

1. For the 1st order reaction whose rate law constant, k, is 1.5x10-3s-1, t½ is a. 7.7 minutes *** b. 462 minutes c. 6.5 minutes d. 4.5 minutes 2. If the half-life of a 1st order reaction is 137 minutes, k= a. 8.43x10-5s-1 b. 11,900 s-1 c. 5.06x10-3s-1

28. ## ChemB

The activity of carbon 14 in living tissue is 15.3 disintegrations per minute per gram of carbon. The limit for reliable determination of age is based on carbon 14 is .10 disintegration per min per gram of carbon. Calculate the max age of a sample that can

29. ## chemistry

The isotype caesium -137, which has a half life of 30 years, is a product of nuclear power plants. How long will it take for the amount of this isotype in a sample of caesium to decay to one-sixteenth of its original amount? first half life 1/2 second 1/4

30. ## Chemistry

Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. How many beta particles are emitted in 190s by a 3.10mg sample of Co-60? What is the activity of the sample in Bq?

31. ## 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

33. ## 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

34. ## Chemistry (Dr.Bob222)

The half-life of P-32 is 14 days. How long after a sample is delivered can a laboratory wait to use a sample in an experiment if they need at least 10 percent of the original radioactivity? I need help on how to set up this problem. What is the general

35. ## chemistry

Upon decomposition, one sample of magnesium fluoride produced 1.65kg of magnesium and 2.58kg of fluorine. A second sample produce 1.38kg of magnesium. How much fluorine (in grams) did the second sample produce?

36. ## Chemistry

Upon decomposition, one sample of magnesium fluoride produced 1.65kg of magnesium and 2.58kg of fluorine. A second sample produced 1.50 kg of magnesium. How much fluorine (in grams) did the second sample produce?

37. ## Physics (Inside the atom)

A sample of radioactive isotope I is to be used for medical diagnosis of the kidneys. The isotope has a half-life of 8.0 days, and the sample is required to have an activity of 8 x 10^5 per second at the time it is given to the patient. Calculate the mass

38. ## 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

39. ## 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

40. ## Chemistry

Po-210 Ia an alpha emitter with a half-life of 138 days. how many grams of Po-210 remain after 552 days if the sample initially contained 5.80g of Po-210?

41. ## science

a radioisotope, Iodine-131, has a half life of 8.1 days. explain what this means. draw a particle diagram for a sample 12 particles of I-131 initially after 8.1 days and after16.2 days.

42. ## 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

43. ## Math

You have just isolated a new radioactive element. If you can determine its half-life, you will win the Nobel Prize in physic. You purify a sample of 2 grams.One of you colleges steals half of it, and 3 days later you find that 0.1 grams of the radioactive

44. ## 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)

45. ## physics lab

For an unknown sample of the experiment, students measure 1602 counts when they first receive their sample and 1317 counts 3.5 minutes later. Calculate the half-life t12 of their sample.

46. ## 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

47. ## math

The half life of the radio active substance is the time require the half the substance to decay. the mount A ( in grams) of 100 gram sample of a radio active substance remaining after t half lives by A equals to 100 (0.5) t. suppose the substance has a

48. ## physics

Suppose 32000 radioactive nuclei are in a sample. About how many remain after two days if the half-life is 22 hrs? What is the initial activity of the sample in decays per minute?

49. ## chemistry

90Sr is one of the harmful radionuclides resulting from nuclear fission explosions. It decays by a first-order process with a half-life of 28 years. How many years would it take for 99.99% of a given sample released in the atmosphere to disintegrate?

50. ## chemistry

A sample of 131 I was purified and then analyzed for iodine content. It was found that the sample was 99.8% pure. 25 hours later the sample was tested again and it was found that the sample was now just 78.2% pure. What is the half - life of 131 I?

51. ## physics

The half-life of Th(227) is 18.72 days. It decays by alfa emission to Ra(223), an alfa emitter whose half-life is 11.43 days. A particular sample contains 10^6 [10E(+6)] atoms of Th(227) and no Ra(223) at time t=0. a) How many atoms of each type will be in

52. ## pre calc

You have a sample of a certain radioactive substance. After two days, thirty percent of the sample has decayed. What is the half-life of the material and how much will have decayed after a week?

53. ## pre calc

You have a sample of a certain radioactive substance. After two days, thirty percent of the sample has decayed. What is the half-life of the material and how much will have decayed after a week?

54. ## Chemistry

Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. How many beta particles are emitted in 190s by a 3.10mg sample of Co-60? What is the activity of the sample in Bq?

55. ## Chemistry

Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. How many beta particles are emitted in 190s by a 3.10mg sample of Co-60? What is the activity of the sample in Bq?

56. ## Chemistry

If a 40 gram sample of radioactive isotope was present at 4pm, but a 5 gram sample remained at 4:30 pm, what is the half-life in minutes?

57. ## chem

A typical dose of a radioactive sample is 27.0 mCi. How long does it take for the activity to reduce to 0.100 mCi? The half life of the sample is 211,000 y.

58. ## 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

59. ## physics

Radioactive nuclei are produced in an irradiated sample at the rate of 10 s-1. If the number in the sample builds up to a maximum of 1000, calculate the mean life and the half-life of the radioactive nuclei Using dN / dt = P - λ N dN / dt = 1000n /10/ 1 =

60. ## chemistry

fluorine-18 half life of 110 min if 100mg was shipped at 8:00 am how many mg are still active at 1;30 pm same day

61. ## physics

Radon 86222Rn is a radioactive gas with a half-life of 3.82 d. If there are initially 400 decays/s in a sample, how many radon nuclei are left after 2 d ? Please help, I don't understand how to do this.

62. ## Ap chemistry

if a 84g sample of thorium decays with a 10 minute half life, how much would the sample weight in a half hour?

63. ## chemistry

Upon decomposition, one sample of magnesium fluoride produced 1.66kg of magnesium and 2.56kg of fluorine. A second sample produced 1.29kg of magnesium. How much fluorine (in grams) did the second sample produce?

64. ## College Chemistry

Upon decomposition, one sample of magnesium fluoride produced 1.66kg of magnesium and 2.56kg of fluorine. A second sample produced 1.25kg of magnesium.How much fluorine (in grams) did the second sample produce?

65. ## Chemistry

Upon decomposition, one sample of magnesium fluoride produced 1.65kg of magnesium and 2.58kg of fluorine. A second sample produced 1.38kg of magnesium. How much fluorine (in grams) did the second sample produce?

66. ## Chemistry

one sample of magnesium fluoride produced 1.65kg of magnesium and 2.58kg of fluorine. A second sample produced 1.31kg of magnesium. How much fluorine (in grams) did the second sample produce?

67. ## modern physics

A radioisotope P has a half-life of 3 s. At t = 0, a given sample of this isotope contains 8000 atoms. Calculate (i) its decay constant, (ii) average life, (iii) the time t1 when 1000 atoms of the isotope P remain in the sample, and (iv) number of decays

68. ## Chemistry

Nitrogen dioxide decomposes at 300°C via a second-order process to produce nitrogen 14) monoxide and oxygen according to the following chemical equation. 2 NO2(g) → 2 NO(g) + O2(g). A sample of NO2(g) is initially placed in a 2.50-L reaction vessel at

69. ## 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

70. ## chemistry

A radium-226 sample initially contains 0.112mol. How much radium-226 is left in the sample after 6400 years. The half-life of radium-226 is 1600 years.

71. ## chemistry

Some radioactive nuclides have very short half-lives, for example, I-31 has a half-life of approximately 8 days. Pu-234, by comparison has a half-life of 24,000 years. Explain why both of these examples are dangerous, even though their half-lives are very

A Cesium 137 sample has a measured radioactivity of 50 microcuries.Cesium 137 has a half-life of 30 years. How long will it take this sample to be reduced to a residual radioactivity of 6.25 microcuries? Is there a formula to calculate half life?

73. ## Chem

Upon decomposition, one sample of magnesium fluoride produced 1.65 of magnesium and 2.57 of fluorine. A second sample produced 1.38 of magnesium. How much fluorine (in grams) did the second sample produce?

74. ## Chemistry

Upon decomposition, one sample of magnesium fluoride produced 1.64 kg of magnesium and 2.57 kg of fluorine. A second sample produced 1.38 kg of magnesium. How much fluorine (in grams) did the second sample produce?

75. ## chemistry

Upon decomposition, one sample of magnesium fluoride produced 1.65 kg{\rm kg} of magnesium and 2.58 kg{\rm kg} of fluorine. A second sample produced 1.50 kg{\rm kg} of magnesium. How much fluorine (in grams) did the second sample produce?

76. ## chem

The half-life of the Nobelium isotope No^257 is about 23 seconds. 644 seconds (or 28 half-life periods) after the isotope was released there were 20 grams remaining. The number of grans of No^257 after h half life periods is M= 20 * (1/2)^h where h = 0

77. ## 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?

78. ## physics

A building has become accidentally contaminated with radioactivity. THe longest lived material in the building is strontium-90 (atomic mass of 90 Sr 38 is 89.9077). If the building initially contained 5.0kg of this subtstance and the safe level is less

79. ## Science

An element has a half-life of 30 years. If 1.0 mg of this element decays over a period of 90 years, how many mg of this element would remain? Begin amount is 1.0 elapsed time is 90y half life 30 years n=9/30 n=3 90/2^2 90/8 = 11.25mg thinking it's wrong

80. ## Physics (I have a test tmrw)

The half-life of Strontium-90 is 28 a. If 60 g of this isotope is currently in a sample of soil, estimate the amount in the same sample 84 a later. So I did a=60g(1/2)^84/28 But I don't know if thats correct. Thank for your help!

81. ## science

Carbon-14 has a half-life of approximately 5,730 years. How many half-lives have occurred in a sample that contains 50 percent of the original amount of the parent isotope?

82. ## SCIENCE

We did a radioactive decay and half life lab with m&ms and I do not understand these conclusion questions: 1. how many half lives would it take for 500 nuclei to decay to 6.25% of the original number of nuclei? My ans: 3125?- do not think that's right! 2.

83. ## 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

84. ## 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

85. ## calculus

The half-life of a certain radioactive sub- stance is 8 hrs. There are 5 grams present initially. Which of the following gives the best approximation when there will be 1 gram remaining?

86. ## nuclear

Calculate the age of a plant sample that shows about one-eighth of the carbon 14 of a living sample. The half-life of carbon-14 is about 5760 a. Help please...

87. ## nuclear physics

Calculate the age of a plant sample that shows about one-eighth of the carbon 14 of a living sample. The half-life of carbon 14 is about 5760a How do you do this?

88. ## Chemistry

Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. How many beta particles are emitted in 190s by a 3.10mg sample of Co-60? What is the activity of the sample in Bq?

89. ## physical science

A sample of phosphorus-32 has a half-life of 14.28 days. If 55 g of this radioisotope remain unchanged after approximately 57 days, what was the mass of the original sample? help please, im confused.

90. ## Chem

The only stable isotope of fluorine is fluorine-19. Predict possible modes of decay for fluorine-21, fluorine-18, and fluorine-17. Would it just be alpha-particle production, beta-particle production, gamma-ray production, and positron production for all

91. ## physics

How do I do this ? Calculate the age of a plant sample that shows about one-eigth of the carbon 14 of a living sample. The half-life of carbon-14 is about 5760a I don't have the notes on how to do this one... Help

92. ## Chemistry

If 25.0 g of a radioactive sample is left after 100.0 years and each half-life is 25 years, how much sample did you start with?

93. ## Chemistry

To an initially evacuated 50.0L container maintained at 155C were added 3.20g of gaseous xenon and 4.00g of gaseous fluorine. A spark was used to initiate reaction between xenon and fluorine, and gaseous xenon hexafluoride was the sole reaction product.

94. ## Physics ...

116In nuclei are produced at the rate of 10 s-1. Calculate the maximum number of 116In nuclei (number in equilibrium) in the sample if the half-life of 116In is 54 m. So far I have come up with ... The half life = 54m x 60 s-1 = 3.24 x 103 s-1 (In2) / λ =

95. ## Chemistry

Fluorine-18, which has 1/2 life of 110 minutes, is used in PET scans. If 100 mg of fluorine-18 is shipped @8AM, how many milligrams of the radioisotope are still active if the sample arrives at the lab at 1:30 pm?

96. ## Chemistry

Upon decomposition, one sample of Magnesium Fluoride produced 1.65 kg of magnesium and 2.57 kg of fluorine. A second sample produces 1.33 kg of magnesium. How much fluorine (in grams) did the second sample produce?

97. ## 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?

98. ## Chemistry

The half-life of C-14 is 5700 years. If it took seven half lives for a sample of C-14 to decay completely, how many years would have gone by?

99. ## 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

100. ## Science HELP 2nd question

A sample originally contained 2.5 g of rubidium 87 now contains 1.25 g. The half life of rubidium - 87 is 6 x 10 ( to the 10th) years. How old is the sample? Is this possible? why or why not?