## anonymous one year ago HAlf Life problem Radon-222 has a half-life of 4.0 d (abbreviation for “diem”—Latin for “day”). If the initial mass of the sample of this isotope is 6.8 g, calculate the mass of radon-222 remaining in the sample after: a) 8 d b) 16 d c) 32d the awnsers are : a) 1.7g b)0.62g c) 0.026g i can't figure out how to do it

1. anonymous

You mean 0.42 for b?

2. anonymous

no it is 0.62 for 6 this question is from a text book with given awnsers

3. anonymous

Check it again.

4. anonymous

i will show you a picture one second

5. anonymous

Kk.

6. anonymous

7. anonymous

its a word file

8. anonymous

Is that the only you cant figure or is it all of them?

9. anonymous

It is probably a typo as I know I got a and c right. If b is between the ones I got right, then I am sure it is a mistake

10. anonymous

Is that really a textbook? If so, what publisher is it?

11. anonymous

12. anonymous

and i can't figure out how to do all 3

13. anonymous

i think it is called nature of matter 11 thre could have possible been a mistake, they are common in textbooks

14. anonymous

$Half life period=\frac{ \ln2 }{ k }$ Mass after some days is given as y(t) where t is the time in days y0 would be initial mass. Formula for mass after some days is $y(t)=y _{0}e ^{-kt}$

15. anonymous

Try it and would get a and c right but not b. Strange.

16. anonymous

okay ty i will try it and see if i get the awnser right

17. anonymous

KK, I can wait.

18. anonymous

in the formula you put -kt what does that represent?

19. anonymous

as the expoenet

20. anonymous

There would be a negative sign because it is decaying. k is the constant from knowing the half life period. t is the time in days

21. anonymous

with the formula i am doing y(8)=6.8 and im am confused for what i do after

22. anonymous

because i am still getting the wrong answer

23. anonymous

can you do a question so i know how its done

24. anonymous

you forgot yo use the e^-kt part.

25. anonymous

to*

26. anonymous

You done e before in Algebra right?

27. anonymous

yeah it's the exponent right? i didnt know what values would go for the k

28. anonymous

Read my explanation above for the formula.

29. anonymous

lol i did but i still dont understand

30. anonymous

we briefly learned this in class so i am very confused

31. anonymous

Half life period is the period it takes for an element to lose half its mass

32. anonymous

which was four days

33. anonymous

so is the k value supposed to be 4

34. anonymous

Yes! Now solve for k

35. anonymous

No. Read my 2 formulas above.

36. anonymous

what does the IN mean?

37. anonymous

Oh man, I thought algebra 2 was needed to take chemistry. ln is natural logarithm. But dont worry about its meaning since you probably havent took algebra 2 yet. It is in a scientific calculator. Do you see it. Its actually lowercase of L then n, not in btw.

38. anonymous

yeah i found it now i can solve for k using this

39. anonymous

btw this is highschool chemistry fir grade 11 and you only need grade 10 scince to be able to take it :P

40. anonymous

is k value 1.45?

41. anonymous

How?

42. anonymous

beacuse in*2 *1.45=4

43. anonymous

$4=\frac{ \ln2 }{ k}$ Cross multiply $4k=\ln2$ Divide both sides by 4 $4=\frac{ \ln2 }{ k }$

44. anonymous

Dont forget to close the parentheses inside the ln

45. anonymous

i am getting 0.17

46. anonymous

if this isnt correct i will ask my chemistry teacher at school tom

47. anonymous

im very confused right now

48. anonymous

Yea you are correct. But makes but includes the other decimals. I got 0.1732

49. anonymous

yeah i rounded

50. anonymous

Now do a).

51. anonymous

yeah i fiannly got the right awnser

52. anonymous

tysm for helping me

53. anonymous

No problem! Just remember the formula and its meanings and you're all good.

54. anonymous

Okay thank you