Question

An experiment is conducted to investigate the kinetics of reaction between bromopropane and 0.1 moldm^-3 of sodium hydroxide. The rate equation is as follows: Rate = K[bromopropane][oh-]. The half-life of bromopropane in one of the experiments is T minutes. What is the new half life(in minutes) of bromopropane when the concentration of bromopropane is doubled and concentration of sodium hydroxide is reduced to 0.01 moldm^-3 ?

Answer 1

stuck at this question for a long time =( would appreciate any help given.

Answer 2

this is indeed a tricky one.

this will take time.

Answer 3

are you sure that this ques. has nothing misssing?? or nothing incorrect??

i am just asking...

Answer 4

no there is nothing, it is a preliminary question from one of my schools here... dam its tough

Answer 5

i can give you options, gimme a min

Answer 6

yup .... it is.. tough...

i am trying..
i am hoping to get the answer...

Answer 7

A .0.05 T
B. 0.1T
C. 5T
D. 10T

Answer 8

it's night time.... and i must go now.
i will try this ques. tomorrow..
i m going right now.

this ques. is really very .. difficult.

Answer 9

for the second scenario in which A + B → P, the half-life of the reaction cannot be determined! because ln[B][A]o[A][B]o=k([B]o−[A]o)t

Answer 10

it can =/

Answer 11

i roughly know that u musnt take into account the changes occuring to bromoproapne because we are only concern with the half life of bromopropane and not the overall reaction

Answer 12

but the problem is i dont know how to go about doing it

Answer 13

i thought about that it is a second order reaction that the reactants are not the same. and we do not know anything about the initial concentration of bromopropane.

Answer 14

yes it is a second order reaction, but it is first order with respect to bromopropane

Answer 15

so concentration of bromopropane against time would result in having a constant half life

Answer 16

this goes for oh- too

Answer 17

it is only second order overall reaction

Answer 18

but i think that the half lives are dependent on each other.

Answer 19

i get what u mean.. but thats what i've been learning so far =(

Answer 20

if its first order with respect to a concentration.. u will get a constant half life

Answer 21

It is SN2 reaction. it has only one step. it is second order most of the times.

Answer 22

yes but reaction is first order with respect to bromopropane, thus plotting [bromopropane] against time will give u a constant half life, but if u plot [bromopropane][Oh-] against time, u will not get a constant half life

Answer 23

its only second order overall reaction, now we r only concern with a single reactant, not both

Answer 24

is it true that you look at the components separately?

Answer 25

yes, i believe we have to.. O.O

Answer 26

:) where did you get this question?
can I see your source?

Answer 27

Im from singapore =/, the source is from National junior College preliminary examination 2012

Answer 28

dont worry, i double check the qn and made sure i wrote it all down correctly

Answer 29

do you have the answer of this ques???
is it 10T??

Answer 30

yes it is 10T =D teach me pls!

Answer 31

i put 5T as my answer...

Answer 32

wait for some time ,..
i am solving a ques.

as soon as i am done withi this one, i will tell you how i arrived at the sol.

PS. i don't know it is right or not.

Answer 33

ok!

Answer 34

this formula helped me..

Answer 35

AND THIS ONE TOO

Answer 36

NOW, WHAT I DID WAS, USED THE FORMULA HIGHLIGHTED IN GREY. AND CALCULATED THE HALF LIFE IN TWO CASES.

CASE 1 : WHEN BROMOPROPANE AND NaOH ARE SAY... X AND 0.1
CASE 2: WHEN BROMOPROPANE AND NaOH ARE 2X AND 0.01

CALCULATED THE HALF LIFE IN HE TWO CASES.........


ARE YOU FOLLOWING WHAT I AM SAYING???????????????????

Answer 37

ITS COMPLICATED.. I KNOW

Answer 38

how do u find the half life ? @.@

Answer 39

using the greyed formula

Answer 40

yes,,,

Answer 41

hmmm.... integrated rate law @.@

Answer 42

what happened????????

you type a message,,,,
then erase it....
:)

hard to comprehend?

Answer 43

its not in my syllabus! D=

Answer 44

yes.. absolutely... integrated rate law

Answer 45

????????????? wat??????????????????????

integrated rate law not in sylabus??

Answer 46

yes means i do not learn it XD, so they wanted to use what we've learnt from the simple rate equation to deduce the answer...

Answer 47

for half life, you need to know integrated rate law...

Answer 48

i learn the formula T1/2 = ln(2)/k

Answer 49

i think i will learn the rate law in university if i wish to carry on chemistry =/

Answer 50

integrated*

Answer 51

this is for the first order equation.
and this one comes from the integrated rate law for first order equation.
by putting the conc. at time t = 1/2 of the initial conc.

yup u will..
but if u are asked this question of half life, then?

Answer 52

i manged to solve the question using T1/2 = ln(2)/ k[oh-] . so when [oh-] is divided by 10, t1/2= 10T relative to the initial experiment. But my tutor said it was wrong because that the equation i was using only applies to pseudo-zero order reaction

Answer 53

is it true its only for pseudo-zero? =/

Answer 54

yes,, your teacher is right in saying this..

you can't use first order equation to solve second order problem

Answer 55

T.T then i have no clue... because if i used that formula you gave me.. i wont finish the paper on time.. its a multiple choice question and we're only given 1.8 mins for each question T.T

Answer 56

anyway THX anish, at least i know how to derive the answer now

Answer 57

seeriously????????????????????????????????

i mean 1.8 mins for a question like this???

Answer 58

or.. how the answer was derived XD

Answer 59

:0

Answer 60

yes, we have 1.15 hours to finish 40 questions of multiple choices =(

Answer 61

welcome to.. singapore

Answer 62

where r u from anish? =)

Answer 63

:)

that's not fair..

i think a question like this is in your paper just to kill your time.. i suppose..

Answer 64

i am from INDIA.

Answer 65

oooo! we had an exchange visit from india not long ago! =O

Answer 66

do u know of a school called CJC in short from india?

Answer 67

not sure which part though..

Answer 68

CHRIST JUNIOR COLLEGE??
ITS IN BANGALORE....

SOURCE -- GOOGLE :)
https://www.google.co.in/#sclient=psy-ab&q=CJC+SCHOOL&oq=CJC+SCHOOL&gs_l=hp.3..0l2j0i22i30l2.2256.7239.0.10211.10.10.0.0.0.0.269.2165.2-10.10.0.ernk_timepromotionb..0.0...1.1.17.psy-ab.XbrrUcM5swg&pbx=1&bav=on.2,or.r_cp.r_qf.&bvm=bv.47883778,d.bmk&fp=9410b04d0e27bfd9&biw=1252&bih=527

Answer 69

yes! its christ junior college!

Answer 70

BUT I NEVER HEARD OF IT...
:(

Answer 71

ohhh haha XD im from catholic junior college in singapore, in short for cjc too XD

Answer 72

you're in university alrdy? studying chemistry?

Answer 73

:-)

i think that's precisely why they came there..

yes. i am pursuing my graduation in chemistry

Answer 74

yea haha XD chemistry as in theroretical chemitry?

Answer 75

i dunno what course to take for university and im 4 months away from my A levels @.@

Answer 76

well.......... take the subject in which you have interest...

Answer 77

true... haha XD. aight thx anish!

Answer 78

welcome... ezizio...!!

Answer 79

u from singapore na???

Answer 80

na?

Answer 81

delete the na..
:)

u from singapore..?

Answer 82

oh haha yea i am XD

Answer 83

you've been here?

Answer 84

no.. not yet....

Answer 85

but someday........ i want to go and see places like singapore ...

Answer 86

now i can tell my friends that i have an international friend..:::
an acquaintance from singapore..:P

Answer 87

o.o singapore is very small and boring XD but its a nice place to live in haha XD

Answer 88

:-P

Answer 89

lol! same here =D, but after my exams.. i have to serve national service for two years haha XD full time

Answer 90

national service????
millitary??

Answer 91

yea the military for two years =/

Answer 92

it's compulsory for all males...

Answer 93

isnt it..??

Answer 94

yea o.o you served yurs too?

Answer 95

dude.... this is awesome.....

u know something??
i had always dreamt of joining army....
but due to poor eyesight, i am not eligible to go in army..

but in singapore, all males go to army,....
wish i was in singapore..:(

no, i haven't served.... but i wanted to.:!

Answer 96

O.O i see =(, but 2 years is a long time =(...2 yearsof my life is wasted D=

Answer 97

no. no.. not wasted,,,
its good.. its very good..

army.. discipline, good physique, u will learn to work in a team...for your country..

u know something..??

it is you who will be going to the army.. but i am feeling excited about it....:)
strange,,, isnt it?