# how many half-lives have passed if 87.5% of a substance has decomposed?

86,566 results

1. ### Chemistry

How many half-lives have passed if 87.5% of a substance has decomposed? How many if 99.999% has decomposed? For 87.5% decomposition 1/8 is left. (1/8) = (1/2)^3 Three half lives is the answer Fot 99.999% decomposition, 10^-5 is left. Solve 10^-5 = (1/2)^n for the number of ...
2. ### science

how many half-lives have passed if 87.5% of a substance has decomposed? how many if 99.999% has decomposed?
3. ### Science

If the initial amount of Carbon-14 in the mammoth was 8 grams, how many half-lives have passed i the fossil sample has 1 gram left? How many years have passed since the mammoth's death?
4. ### 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 half life of 10 days. ...
5. ### chemistry

how many half-lives of radon-222 have passed in 11.46 days?
6. ### science

Using absolute dating,a fossil is dated to be 3 million years old and decomposed 1 half-life. If it takes the same fossil 12 million years to decompose to 4 half-lives,how old will the fossil be when it is measured to be at 3half-lives?
7. ### Chemistry

how many half lives have passed if only 0.625g remain of the original 40g?
8. ### Exponential Modeling

The half-life of a radioactive substance is one day, meaning that every day half of the substance has decayed. Suppose you have 100 grams of this substance. How many grams of the substance would be left after a week?
9. ### Chemistry

K-42 has a half-life of 12.4 hours. If you begin with 250g of K-42, determine how much you will have left after 4 half-lives. How long does 4 half-lives take? please help
10. ### Chemistry

How do you calculate the amount of a radioactive substance remaining after an integral number of half-lifes have passed?
11. ### chemistry

what fraction of an original sample of a radioactive isotope remains after three half-lives have passed? 1/8?
12. ### science

how many half-lives have passed if only 1/16 of the original amount of the element remains? a-two b-three c-four d-five
13. ### physical science

a scientist found a fossilized bison. using Carbon-14 dating, she found that the fossil was about 45,840 years old. Carbon-14 has a half-life of 5730 years. how many half-lives have passed?
14. ### 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)
15. ### 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 A’, which represent the rate of decay of the substance. b) what is the half-life for this substance? c) ...
16. ### algebra

1) how many billions of years will it take 1000 grams of uranium-238 to decay to just 125 grams? 2) a researcher had 37.5 g left from a 600 g sample of sulfer-35. how many half-lives passed during that time? 3) look at problem 2. how many days passed during that time?
17. ### Science

Please respond I have this last question and then I can be done this course Using absolute dating,a fossil is dated to be 3million years old and decomposed 1half-life. If it takes the same fossil 12million years to decompose to 4half-lives, how old will it be when it is ...
18. ### Science

13.)How can substance A and B be compared? Choose all that apply. A.)The particles of substance A have more energy than the particles of substance B.*** B.)The particles of substance A are more tightly held together than the particles of substance B. C.)The particles of ...
19. ### Math

1. Iodine-131 is used to find leaks in water pipes it has a half life of 8.14 days. If 36 days have passed and there is now 2.34g left. What is the initial amount? 2. Sr-85 is used in bone scans and has a half life of 64.9 days. If there is 23 percent of the sample remaining ...
20. ### Algebra

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 ...
21. ### Calculus

a certain radioactive substance is decaying so that at time t, measured in years, the amount of the substance, in grams, is given by the function f(t)=3e^-3t. What is the rate of decay of the substance after half a year: I first found the derivative of f(t)=3e^-3t which is f'(...
22. ### 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...
23. ### 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 ...
24. ### 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....
25. ### 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 ...
26. ### Math

A radioactive substance decays according to the formula Q(t) = Q0e−kt where Q(t) denotes the amount of the substance present at time t (measured in years), Q0 denotes the amount of the substance present initially, and k (a positive constant) is the decay constant. (a) ...
27. ### Math

A radioactive substance decays according to the formula Q(t) = Q0e−kt where Q(t) denotes the amount of the substance present at time t (measured in years), Q0 denotes the amount of the substance present initially, and k (a positive constant) is the decay constant. (a) ...
28. ### science

A 10g sample of radioactive substances is lift to decay for five half-lives. How much of the radioactive substance remains?
29. ### Math

the half life of a radioactive substance is one day. You have 100 grams. how much of the substance would be left after a week?
30. ### chemistry

If you have 12 moles of a substance, how many molecules do you have of that substance? Suppose the substance has a molecular weight of 342. How many grams of that substance would you have to dissolve in a liter of water to make a 12 M solution?
31. ### Chemistry

Based on mass spectrometer analysis of Uranium-235 and Lead-207, I have determined the age of a zircon to be 89.125 million years old. How many half-lives passed? What are the percentages of Uranium-235 and Lead-207?
32. ### chemistry

Based on mass spectrometer analysis of Uranium-235 and Lead-207, I have determined the age of a zircon to be 89.125 million years old. How many half-lives passed? What are the percentages of Uranium-235 and Lead-207?
33. ### Chemistry

About twenty radioisotopes with ultra-long half-lives, from 82 million years (244- Plutonium) to 6 million billion years (50-Vanadium) are found in the earth’s crust, yet no radioisotopes with half-lives less than 70 million years (146- Samarium) are found. Why not? Use this...
34. ### algebra

A radioactive substance decays according to the formula A=A0e^kt where A0 is the initial amount of substance (in grams) A is the amount of substance(in grams) after t years k is a constant The half-life of the substance is 10 years.If we begin with 20g of the substance,how ...
35. ### calculus

assume the half-life of the substance is 31 days and the initial amount is 183.9 grams. (a) Fill in the right hand side of the following equation which expresses the amount A of the substance as a function of time t (the coefficient of t in the exponent should have at least ...
36. ### 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?
37. ### math with application

If 12 % of a radioactive substance decays in 7 hours, what is the half-life of the substance? Carry out all calculations exactly, then round the final answer to three decimal places. The half life is what hours?
38. ### Chemistry

Which substance can not be decomposed by ordinary chemical means? how? 1. methane 2. mercury 3. ethanol 4. ammonia
39. ### 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?
40. ### Chemistry

For my homework the question is... What is the half life of polonium 214 if a 1 gram sample decays to 31.25mg after 820 seconds? Im not sure how you arrive at the answer, my friend says the answer is 5 but were not sure how to do it..thanks for any help u may have ln(No/N)= kt...
41. ### Physics

Suppose a hypothetical radioactive nucleus (Hy) has a half-life of 10 days. If we have 80 gms of the substance at the start of an experiment, how many gms of the substance will remain undecayed after 30 days
42. ### Calculus-derivatives

Verify if these are correct answers. 1. The derivative of f(x)=e^2x -e^-2x is f'(x)=2e^2x - 2e^-2x? 2.A certain radioactive substance is decaying so that at time t, measured in years, the amount of the substance, in grams, given by the function f(x)=3e^-3t. What is the rate of...
43. ### PLS HELP ASAP 1 SUPER HARD & ANNOYING QUESTION

Use the diagram to answer question 13. so substance A looks like a row of three little circles on the top and bottom all organized (total six dots). substance b is all clumped together circles and is disorganized. 13. How can substance A and B be compared? Choose all that ...
44. ### math

A professor knows that in her class 37% of the students have passed an Algebra course, 29% have passed an English course, and 21% have passed both courses. If one student is selected at random from this class, find the probability that:
45. ### 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?
46. ### Physics

A radioactive substance decays from 2.0kg to 1.6kg in 156 days. What is the decay constant and the half life of the substance?
47. ### 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 ...
48. ### Physics

A radioactive substance has a half life of 60s.what fraction of the original substance would you expect to exist after 180s.
49. ### CALCULUS

Let y(t) denote the mass of a radioactive substance at time t.t. Suppose this substance obeys the equation y′(t)=−14y(t). Assume that, initially, the mass of the substance is y(0)=M>0. At what time does half of the mass remain? (Round your answer to 3 decimal ...
50. ### math

an extremely volatile substance, Ofnetite, has a half-life of 25 minutes. Find the percentage decrease of this substance in the first two hours.
51. ### College Calculus

A radioactive substance has a half-life of 27 years. Find an expression for the amount of the substance at time t if 20 grams were present initially.
52. ### chemistry

Which of the following is true of a substance with a pH of 11.0? A. The substance is an acid. B. The substance is a base. C. The substance is neutral. D. The substance is a transition metal. I think A
53. ### math

if the rate for radioactive decay for a substance is r=-.0063 and time is being measured in days how do you find the half-life of the substance to the nearest hour?
54. ### Algebra 2

A radioactive substance decays at a rate of y = ae^-0.1483t, where t in in hours. Find the half-life of the substance. How do I solve this problem if I am only given the constant.
55. ### 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...
56. ### chemistry

Examine the information. Element A has a half-life of 10 days. A scientist measures out 200 g of this substance. After 30 days has passed, the scientist reexamines the sample.  How much Element A will remain in the sample 100g 12.5g 50g 25g is it d?
57. ### Math

Suppose that the half-life of a substance is 250 yrs. .If there were initially 100 g of substance .How much will remain after 500 years??with solution please
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. ### 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 ...
60. ### Math

A radioactive substance decays to the formula N=8e^-0.6t , where N is the number of milligrams present after t hours. Determine the initial amount of the substance to the nearest 10th of an hour, determine the half life of the substance, and determine the number of hours for 0...
61. ### Math

I need help in algebra 1. I have 4 questions, I already answered 3 of them, but I need help with the other 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). 1. Write an exponential ...
62. ### Pre Cal

a radio actice substance decays so that half of the substance decays every 2 minutes. if 100 g of the substance are present initially, how many grams will be present after 4 minutes and 8 minutes respectively?
63. ### Algebra 2

A 14 gram sample of a substance that's used to preserve fruit and vegetables has a k-value of 0.1092. Find the substance's half-life, in days. Round your answer to the nearest tenth.
64. ### chemistry

2. Imagine you have two beakers. Both beakers are filled with the same amount of water. The water in both beakers is the same temperature as well. You add 50 g of Substance A to the first beaker, and 50 g of Substance B to the second beaker. After stirring both beakers, there ...
65. ### chemistry

if you had 120 grams of sugar and all of it decomposed,how many moles of water were decomposed?
66. ### Physics

100g of radioactive element X are placed in a sealed box. The half-life of this isotope of X is 2 days. After 4 days have passed, what is the mass of element X in the box? b) If the box is completely evacuated (perfect vacuum), then N atoms of X are added. After 4 days have ...
67. ### chm

An unknown radioactive substance has a half-life of 3.20 . If 34.8 of the substance is currently present, what mass was present 8.00 hours ago?
68. ### statistics

A professor knows that in her class 37% of the students have passed an Algebra course, 29% have passed an English course, and 21% have passed both courses. If one student is selected at random from this class, find the probability that: c) the student did not pass algebra.
69. ### chemistry

Substance A and substance B react to form substance C as described by the equation: A + B ↔ C If only substance A and substance B are placed in an enclosed vessel and allowed to react what would the reaction be?
70. ### Chemistry

The half life for a first order reaction is know to be 4.5 h. How long will it take for 85% to be decomposed, in h?
71. ### Math/Calculus

After 5 days, a particular radioactive substance decays to 37% of its original amount. Find the half life of this substance. Is this right? Th= ln 2/ln(1/.37) x 5 days
72. ### Geology

If a rock contains an isotope with a half live of 600 million years, and 0.5 half lives have elapsed since the rock formed, how old is the rock in millions of years?
73. ### Pre Calculus

Exponential growth and decay find the half life of a radioactive substance if 220 grams of the substance decays to 200 grams in 4 years?
74. ### Chemistry

Suppose 1.0 mol of substance A reacts with 1.0 mol of substance B. to produce 2.0 mol of substance C. In a reaction, 2.4 mol of substance A is allowed to react with 2.1 mol of substance B. What amount in moles of substance c is produced?
75. ### Chem

which substance cannot be decomposed by a chemical change? carbon dioxide, methane, carbon monoxide, or carbon
76. ### chemistry

the half-life of polonium-218 is 3.0 minutes. what percentage of the original sample remains after 4 half-lives?
77. ### 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. ...
78. ### chemistry

upper atmosphere chloromethane can be decomposed by light according to the reaction:CH3Cl -> CH3(g) + Cl(g)The energy required for this reaction is 428 kJ mol–1. If each molecule of chloromethane is decomposed by one photon, what is the maximum wavelength that photon can ...
79. ### Math

Suppose f(t) = P0e^-0.3t grams of radioactive substance are present after t seconds. If 200 grams of substance are present initially, how much is present after 4 seconds? What is the half-life of the substance?
80. ### English

1. This is the house where he lives. 2. This is the house in which he lives. 3. This is the house that/which he lives in. 4. This is the house that he lives. 5. This is the house he lives. 6. This is the house he lives in. ============== Among the 6 sentences, #4 and #5 are ...
81. ### math

In a group of 105 students, 70 students passed Mathematics, 60 students passed History and 45 students passed Geography; 30 students passed Mathematics and History, 35 students passed History and Geography, 25 passed Mathematics and Geography, and 15 passed all three subjects...
82. ### Math

In a group of 105 students, 70 students passed Mathematics, 60 students passed History and 45 students passed Geography; 30 students passed Mathematics and History, 35 students passed History and Geography, 25 passed Mathematics and Geography, and 15 passed all three subjects...
83. ### chemistry

An unknown substance has a mass of 17.3 . When the substance absorbs 1.557×102 of heat, the temperature of the substance is raised from 25.0 to 45.0 . What is the most likely identity of the substance?
84. ### chemistry

in 1807 the English chemist Humphrey Davy passed an electric current through molten potassium hydroxide and isolated a bright, shiny reactive substance. He claimed the discovery of a new element, which he names potassium. In those days, before the advent of modern instruments...
85. ### math

A researchr assistant made 160mg of a radioactive, and found that there was only 20mg left after 45hours. a) What is the half-life of this substance? b) Write a function to represent the amount of substance left after x hours c) If the researcher kew he needed 100mg of the ...

A radioactive substance has a half-life of 4 days. Suppose we have 800 mg of this substance. a) Find the equation of the mass remaining after t days. Use the exact value for k not a decimal approximation. b) Rounding your answer to the nearest tenth of a mg, find the mass ...

A radioactive substance has a half-life of 4 days. Suppose we have 800 mg of this substance. a) Find the equation of the mass remaining after t days. Use the exact value for k not a decimal approximation. b) Rounding your answer to the nearest tenth of a mg, find the mass ...
88. ### Chemistry

After 79 mins 20.0% of a compound has decomposed. What is the half life of this reaction assuming first-order kinetics?
89. ### chemistry

After 56.0 min, 25.0% of a compound has decomposed. What is the half-life of this reaction assuming first-order kinetics?
90. ### Chemistry

After 53.0 min, 14.0% of a compound has decomposed. What is the half-life of this reaction assuming first-order kinetics?
91. ### Chemistry

After 62.0 min, 11.0% of a compound has decomposed. What is the half-life of this reaction assuming first-order kinetics?
92. ### Chemistry

A forensic scientist is given a white substance that is thought to be cocaine. The substance is found to have a percent composition: 49.48% C, 5.19% H, 28.85% N, and 16.48% O. What is the empirical formula for this substance? Is it cocaine?
93. ### math

500 students sat for an examination in mathematics,physics and chemistry.45 passed all the three subject,60 passed mathematics and chemistry,70 passed physics and chemistry,50 passed mathematics and chemistry,10 passed in mathematics,80 passed in chemistry and 35 passed at ...
94. ### chemisrty

When a substance changes from one phase to another, which of the following occurs? the substance loses or gains heat the average kenetic energy of the substance changes the temperature of a substance changes the molecular motion of a substance changes
95. ### English

What is the theme of the poem Home for the Aged? Home For the Aged by Elizabeth Brewster: The old men sit, five of them on a bench, Half sleeping, half awake, dazed by the sun, In the muted afternoon, between one broadcast ball game and the next Their thoughts are leaves that ...
96. ### precal

If the half-life of a certain radioactive substance is 2000 years, estimate how many years must elapse before only 35% of the radioactive substance remains?
97. ### Math-Exponential Decay

A lab technician had 58 grams of a radioactive substance. Ten days later, only 52 grams remained. Find the half-life of the radioactive substance.
98. ### chemistry

If, for a second-order reaction, the elapsed time after the first half-life is 338.871 seconds, the elapsed time after four half-lives would be (in minutes)... t1/2= 1/k(A). k= 1/t1/2*(A)=1/338.871 s(1) (I let (A)=1). k = ?? After 4 half lives, beginning of the 5th, (A) = 1/24...
99. ### 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 ...
100. ### 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 ...