Number of results: 16,648

**Science**

Half-life is a measure of the rate of decay of an isotope. True False I think it is false?

*February 12, 2013 by Cassie*

**DPS**

An isotope has a 12.4 hour half life. If it has an activity of 30mCi at noon today, what was its activity at 3 p.m. yesterday?

*April 2, 2013 by Gajender Goswami*

**Physics**

Half life of radium is 44 years.The sample will reduce to 50% of its orignal value ater how many years?

*November 5, 2014 by M.Junaid*

**Chemistry**

The rate constant for a second-order reaction is 0.54 M-1s-1. What is the half-life of this reaction if the initial concentration is 0.27 M

*December 9, 2014 by anonymous.*

**JNV**

An isotope has a 12.4 hrs half-life. If it has an activity of 30mCi at noon today, what was its activity at 3 pm yesterday?

*August 3, 2015 by VSG*

**math calculus**

Find the half-life (in hours) of a radioactive substance that is reduced by 30 percent in 40 hours.

*August 30, 2015 by Urgent help*

**Energy**

If the half life of Ir - 131 is 42 days, how much would be remaining after 168 days?

*October 6, 2016 by katie*

**Physics**

Half life of radium is 44 years.The sample will reduce to 50% of its orignal value after how many years?

*January 28, 2017 by Salman*

**Chemistry**

Can you have one half-reaction take place, without the other half-reaction taking place immediately? The other half-reaction takes place when the cell potential is raised. I half witness this in some electrochemical cells. Sincere Thanks.

*November 15, 2010 by Frances*

**CHEMISTRY**

The half-cell, Tl | Tl+(1 mol L-1), is connected to a Pt | H+ | H2(1 atm) half-cell in which the concentration of H+ is unknown. The measured cell voltage is 0.0841 V and the Pt | H2 | H+ half-cell is the cathode. Standard reduction potentials are given on the next page. (a) ...

*November 27, 2012 by sabrina*

**CHEMISTRY**

The half-cell, Tl | Tl+(1 mol L-1), is connected to a Pt | H+ | H2(1 atm) half-cell in which the concentration of H+ is unknown. The measured cell voltage is 0.0841 V and the Pt | H2 | H+ half-cell is the cathode. Standard reduction potentials are given on the next page. (a) ...

*November 28, 2012 by sabrina: Anyone know how to answer this?*

**CHEMISTRY**

The half-cell, Tl | Tl+(1 mol L-1), is connected to a Pt | H+ | H2(1 atm) half-cell in which the concentration of H+ is unknown. The measured cell voltage is 0.0841 V and the Pt | H2 | H+ half-cell is the cathode. Standard reduction potentials are given on the next page. (a) ...

*November 28, 2012 by sabrina: Can someone please help!*

**Chemistry Numerical**

The half life period of a radioactive element is 27.96 days. Calculate the time taken by a given sample to reduce to 1/8th of its initial activity

*November 20, 2014 by Harsh*

**Chemistry**

Technetium-99 has been used as a radio graphic agent in bone scans. If the isotope has a half life of 6.0 hours, what amount is left of 10.0 mg after 2 days?

*November 2, 2016 by Please help*

**chemistry half reactions**

How do i solve this half reaction with Mg(OH)2(s) --> Mg(s)? Complete and balance the displayed half reaction in basic aqueous solution taking into account the electrons. Mg(OH)2(s) → Mg(s)

*November 23, 2010 by Confused*

**chemistry**

Strontium-90 has half-life of 28 years. if a 1.00-mg sample was stored for 112 years. what mass of Sr-90 would remain?

*April 6, 2010 by bob*

**Pre calc**

If 250 mg of a radioactive element decays to 200 mg in 48 hours, find the half-life of the element

*April 28, 2010 by Dom*

**chemistry**

The half life of phosphorus -32 is 14.3 days. What percentage of an original samples radioactivity remains after 57.2 days?

*May 7, 2012 by matt*

**Chemistry**

Chromium-48 has a short half-life of 21.6 h. How long will it take 360.00 g of chromium-48 to decay to 11.25g. Please help me

*December 11, 2012 by Cindy*

**Chemistry**

A radioactive element has a half-life of 6.41 days. What percent of the original sample will be left after 15.0 days?

*January 6, 2013 by John*

**physical science**

sodium-24 has a half life of 15 hours,how much of a 50 gram sample will be left after 60 hours

*February 16, 2013 by sue moore*

**Algebra**

An isotope has a half-life of 97 years. how much of a 19-gram sample is left after 150 years?

*November 13, 2014 by Miles*

**Radioactivity**

Iodine-131 is a radioactive isotope. After 8.00 days, 50.2% of the sample remains. What is the half life of 131-I?

*September 28, 2015 by Jessica*

**Science**

The half-life of randon-222 is 8 days. What was the original mass if 6 grams remains after 24 days?

*February 19, 2016 by Sarah*

**Calculus**

An artifact was found with 63.8% of Carbon 14, how old is the mummy, assuming the half-life of Carbon 14 is 5730 years.

*March 27, 2016 by Homework Help*

**math**

I asked the following the other day and received the following answer: Posted by Matthew on Sunday, March 17, 2013 at 11:03pm. A quantity of oxygen gas had 16.32 g of the radioactive isotope oxygen-19 in it. When measured exactly 10 minutes later, the amount of oxygen-19 was 0...

*March 18, 2013 by Matthew*

**chemistry**

The half-life of stronitum-90 is 28 years. How many grams of this nuclide in a 4.00g sample will remain after 112 years?

*April 27, 2010 by Peter*

**Chemistry**

The half-life of xe-133 is 126 hours. Starting with 250 mg, after 500 hours around how many mg remain?

*May 22, 2010 by Lily*

**Chemistry**

A certain radioactive element has a half life of 1 h. If you start with a 1-g sample of the element at noon, how much is left at 3:00 PM? At 6:00PM? At 10:00 PM?

*October 8, 2010 by Jennifer*

**Chemistry**

In 6.20 h a 100 g sample of ag 112 decays to 25 grams. what is the half life of ag 112. I think the answer is 3.10 but I'm not sure. Thanks in advance =)

*June 15, 2011 by Jackie*

**chemistry**

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

*August 27, 2011 by marjani*

**chemistry**

If the radiicativr decay of nuclear explosion contains 90 Sr , with a half life of 28.1 years how long will it take for 99 of this radioaioot to decay

*December 5, 2011 by devin*

**Calc**

Radioactive radium () has a half-life of 1599 years. What percent of a given amount will remain after years?

*April 15, 2012 by Pamela*

**physics**

If a radioactive isotope has a half-life of 1 year, how much of the original sample will be left at the end of the 2nd year?

*August 23, 2012 by Anonymous*

**Chemistry**

Carbon-14 has a half-life of 5730 y. How much of a 144 g sample of a carbon-14 will remain after 1.719 (times) 10 4y?

*December 11, 2012 by David*

**Chemistry**

Carbon-14 has a half-life of 5730 y. How much of a 144 g sample of a carbon-14 will remain after 1.719 (times) 10 4y?

*December 11, 2012 by David*

**physical science**

cobalt-60 has a half-life of 5.26 years, how much of a 500 gram sample will be left after 21 years

*February 16, 2013 by sue moore*

**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?

*August 6, 2013 by Alice*

**physics**

The half-life of a certain radioactive isotope is 32 hours.What fraction of the sample would remain after 16 hours?(a)0.50(b)0.25(c)0.62(d)0.71

*September 22, 2013 by john*

**Chemistry**

The half-life of 232Th is 1.4 * 10^10. Find the number of disintegrations per hour emitted by 1 mil of 232Th in 1 min.

*April 10, 2014 by Nic*

**Chemistry**

The half-life of Th-232 is 1.4E10. Find the number of disintegrations per hour emitted by 1 mol of Th-232.

*April 10, 2014 by Nic*

**isd muscat**

after two hours 1/16th of the radioactive isotope remains undecayed.half life of the isotope is

*April 11, 2014 by saritha*

**Chemistry**

Iodine 131 is a radioactive isotope. After 4.00 days, 70.8% of a sample of 131I remains.What is the half life of 131I?

*April 26, 2014 by Natalie*

**Pre-Calc**

A radioactive isotope has a half life of 8.1 days. If the sample starts with 25 grams, how much will there be after 90 days?

*November 3, 2014 by Jennifer*

**matg**

Cobalt-60 has a half-life of about 5 years. How many grams of a 300 g sample will remain after 20 years? (Points : 1)

*November 6, 2014 by Anonymous*

**chemistry**

The half-life of C14 radioactive is 5760 yr. After how much time will 200 mg C14 sample be reduced to 25 mg?

*May 3, 2015 by yashpal*

**Ethics**

Which of the following answers to the meaning of life did Tolstoy hold prior to his change of heart and mind? my answer is A a. Life has no meaning, and we must embrace that fact. b. Life's meaning is to provide comfort for oneself and one's family. c. Life's meaning is to ...

*February 17, 2014 by Annmarie*

**Ethics**

Which of the following answers to the meaning of life did Tolstoy hold prior to his change of heart and mind? my answer is A a. Life has no meaning, and we must embrace that fact. b. Life's meaning is to provide comfort for oneself and one's family. c. Life's meaning is to ...

*February 17, 2014 by Annmarie*

**algebra**

Homer is giving some cookies to each of his three brothers. To the oldest, he gives half of the cookies and half a cookie. He then gives half of what is now left and half a cookie to his second brother. Finally, he gives half of what is now left and half a cookie to his second...

*November 24, 2009 by john*

**Mathematics**

If a man and a half finishes a job and a half within a day and a half, how many men can finish 3 jobs within 3 days. Please I need help, I am not so sure with my answer of 6. I would like to verify it. THANKS

*June 25, 2013 by xavier*

**English III**

In “Lucinda Matlock,” what is the title character's attitude toward life? A. She thinks life is hard. B. She thinks life is worthwhile. C. She thinks life is boring. This one has to be C because she is happy all the time.

*June 10, 2012 by Anonymous*

**Chemistry**

How much time in years (assume a 365 day yr) would it take for a 1.6678g sample of 239Np to decay to a mass of 0.8671g if it has a half life of 2.030*10^5s

*May 6, 2011 by Jay*

**Science**

_____ is useful for dating very old rocks because it has a half-life of 1.3 billion years. A. thorium-232 B. potassium-40 C. uranium-235 D. carbon-14 is the answer D?

*November 17, 2016 by Kalie*

**Physics help**

how would you investigate if the half life of water dripping from a burette is constant? I know the method but what equation and principle would ya'll use?

*February 17, 2008 by Daggeron*

**Chemistry**

HCO2H(g) ¨ CO2(g) + H2(g) The half-life for the reaction at 550 ‹C is 24 seconds. How many seconds does it take for the formic acid concentration to decrease by 75%?

*November 11, 2009 by Anonymous*

**chemistry**

What is the half-life of a compound if 69 percent of a given sample of the compound decomposes in 59 min? Assume first-order kinetics.

*January 31, 2010 by danielle*

**chemistry**

For the reaction A to products}, the following data were obtained: t=0 s, A}]=0.715 M; 22 s, 0.605 M; 74 s, 0.345 M; 132 s, 0.055 M. What is the half-life of the reaction?

*February 28, 2010 by joe*

**chemistry**

For the reaction A to products}, the following data were obtained: t=0 s, A}]=0.715 M; 22 s, 0.605 M; 74 s, 0.345 M; 132 s, 0.055 M. What is the half-life of the reaction?

*February 28, 2010 by joe*

**chemistry**

For the reaction A to products}, the following data were obtained: t=0 s, A}]=0.715 M; 22 s, 0.605 M; 74 s, 0.345 M; 132 s, 0.055 M. What is the half-life of the reaction?

*February 28, 2010 by joe*

**Chemistry**

half life of tritium is 12.5 years. how much will remain after 100 years if you started wit 256 grams?

*October 14, 2010 by Anonymous*

**chemistry**

the half-life of radon-222 is 3.823 days. what was the original mass if 0.050g remains after 7.646 days?

*October 21, 2010 by Anonymous*

**chemistry**

Iodine-131 has a half-life of 8 days. How many grams of a 12 g sample will remain at the end of 40 days? how do i solve this? i thought it was 12^40=1.5 but that's wrong...

*November 18, 2010 by jess*

**Calculus**

suppose that a population is dying with a half life of of 43years. The initial size is 1600. Find the 1 year DTDS for this population

*February 6, 2011 by Anonymous*

**physics**

if you have an element that starts out at 40g and has a half-life of 10 days, you keep it for 30 days- how much doe you end up with? .

*April 7, 2011 by sandy*

**College Math**

Only 43% ofthe carbon-14 in an artifact remains. How old is the artifact? Would the answer be less than the half life?

*February 19, 2012 by Angel*

**ALGEBRA**

You have 480 grams of a radioactive kind of tin. If its half-life is 10 days, how much will be left after 30 days?

*March 21, 2012 by Anonymous*

**Algebra 2**

half life carbon -14 is 5,730 years. If you start out 50 grams, how long will it take until it reaches 2 grams?

*May 20, 2012 by chels*

**Science**

A certain isotope has a half-life of 12 hrs. How long will it take for 100 ƒÝgr to decay into only 25 ƒÝgr?

*July 15, 2012 by Haley*

**Science**

if a radioactive isotope has a half-life of one year, how much of the original sample will be left at the end of the second year?

*August 23, 2012 by aileen*

**Science**

if a radioactive isotope has a half-life of one year, how much of the original sample will be left at the end of the second year?

*August 23, 2012 by aileen*

**Calculus**

The half-life of Radium-226 is 1590 years. If a sample contains 100 mg, how many mg will remain after 4000 years?

*November 16, 2012 by Anonymous*

**Math**

assume the substance has a half-life of 11 years and the initial amount is 126 grams. How much remains at the end of 8 years?

*January 25, 2013 by Jackie*

**chemistry**

If something originally contained 32.0 g of Po-210, which has a half-life of 10.5 minutes, and was now 73.5 minutes old, how many grams would be left?

*May 13, 2013 by Mary*

**Math**

An unknown radioactive substance has a half-life of 124 years. How long will it take a 67 grams sample to degrade to 18 grams?

*February 17, 2016 by Maria*

**Algebra**

A radioactive kind of nitrogen has a half life of 10 minutes. If you start with 64 grams of the substance, how much will be left after 20 minutes?

*May 6, 2016 by Ana Y*

**Algebra 2**

A particular radioactive element has a half life of 10.0 days. How much is left after 30.0 days if the sample started with 345g?

*November 2, 2016 by Please help*

**Chemistry**

A particular radioactive element has a half life of 10.0 days. How much is left after 30.0 days if the sample started with 345g?

*November 2, 2016 by Please help*

**Quick Math**

I have a question: How would you solve this? a dozen dozen apples at half a dozen dimes a dozen? In this cause is dozen 12? And half a dozen dimes in 60 cents? So half a dozen dozen is 144/2 so that's 72 correct? yes, half a dozen dozen is 144/2 = 72 but I don't know what that...

*December 5, 2006 by Gina*

**science**

Please help me with this question.... The isotope 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 isotope in a sample of caesium to decay to one-sixteenth of its original amount? k = 0.693/t1/2...

*February 5, 2007 by Mary*

**Life of a Soldier**

Could you please give me some points, details explaining life of an average canadain soldier. Ive jotted down a few, but if you could give me some more, that would help me loads. Didn't get many hours of sleep Poor Living Conditions Had to stand out in the trenches daily, had ...

*October 12, 2011 by Anonymous*

**English**

Especially when the game is called life. There can be a champion in each of us, If we live as a winner, If we live as a member of the team, If we live with a hopeful spirit, For life. ----------------------------- This is a poem. What is the meaning of the last expression "For...

*December 11, 2014 by rfvv*

**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.

*November 8, 2009 by katy*

**Chemistry 212**

the half life of F18 is 2.089x10^-4yrs. How long would it take (in days) for F18 to decrease to 78.71% of its initial amount?

*May 10, 2010 by pookie*

**Chemistry-help please!**

The half-life of Xe-133 is 126 hours. Starting with 250. mg, after 500 hours around how many mg remain? A. 63 B. 16 C. 32 D. 125

*May 23, 2010 by Charleze*

**math**

Radioactive radium has a half-life of approximately 1599 years. What percent of a given amount remains after 100 years?

*February 24, 2011 by rachel*

**math**

Radioactive radium has a half-life of approximately 1599 years. What percent of a given amount remains after 100 years?

*February 24, 2011 by rachel*

**chemistry**

caffeine has a half-life of 4.6 hours in the human body.. How long would it take 125 milligrams tritium to decay to 22 milligrams?

*April 11, 2011 by cam*

**Chemistry**

carbon 14 has a half life of 5715 years. If you start with a 5 gram sample of 14C, what mass is left after 15,000 years?

*April 24, 2012 by Mima*

**Chemistry**

A fossil is found to have a C-14 level of 86% compared to living organisms. How old is the fossil?, (the half life of C14 is 5730 years).

*April 27, 2012 by Mima*

**Chemistry**

Carbon-14 has a half-life of 5730 years In a plant fossil you find that the 14 C has decayed to 1/8 of the original amount how long ago was this plant

*September 24, 2012 by Shay*

**Science chemistry**

It takes 1 hour and 17 min. for a 1.000gsample of a certain isotope to decay to 0.121g. What is the half-life of this isotope? plssss helpp

*September 24, 2012 by Shay*

**chemistry**

It takes 1 hour and 17 min. for a 1.000g sample of a certain isotope to decay to 0.121g. What is the half-life of this isotope? plssss helpp

*September 24, 2012 by Shay*

**earth science**

if carbon 14 has a half life of 24 days how much would be left of 220 gram sample after 168 days

*November 29, 2012 by lan*

**earth science**

if carbon 14 has a half life of 24 days how much would be left of 220 gram sample after 168 days

*November 29, 2012 by lan*

**earth science**

if carbon 14 has a half life of 24 days how much would be left of 220 gram sample after 168 days

*November 29, 2012 by lan*

**chemistry**

Carbon-14 has a half-life of 5730 . In a plant fossil, you find that the has decayed to 1/32.0 of the original amount. How long ago was this plant alive?

*December 3, 2012 by niles28*

**Science**

If a 20 gram sample of a radioactive substance has a half-life of 6000 years, how many grams would be present after 18000 years?

*December 5, 2012 by Owen*

**Biology**

The half-life of Carbon-14 is 5730 years. What is the age of a fossil containing 1/16 the amount of Carbon-14 of living organisms? Explain your calculation.

*December 9, 2012 by Melissa*

**UIW**

Neptunium-239 has a half-life of 2.35 days. How many days must elapse for a sample of 239Np to decay to 0.100% of its original quantity

*September 19, 2013 by Anonymous*

**Math**

Suppose you have a cache of radium, which has a half-life of approximately 1590 years. How long would you have to wait for 1/5 of it to disappear?

*March 26, 2015 by Will*