Author Topic: Chemistry doubt  (Read 8062 times)

Offline red_911

  • SF Immigrant
  • **
  • Posts: 75
  • Reputation: 105
  • spread knowledge
Re: Chemistry doubt
« Reply #15 on: May 24, 2010, 11:49:36 am »
Ok remember when concentrated NaCl is electrolyzed:
First the solution contains Na+ Cl- and H+ and OH- (from water). The positive inos go to the cathode, and negative ions to the anode.

At the CATHODE
the H+ ions accept electrons, since it is less reactive than Na (always elements which is more reactive 'likes' to stay in the ionic form)
2H+  2e-  ---> H2

At the ANODE
the Cl- ions give up the electrons more readily than the OH- ions do.
2Cl-  -->  Cl2  +  2e-

what left in the solution is Na+ and OH- which combine to form NaOH

in your ques ..is 'D' .. the indicator solution turns blue at -ve as NaOH is produced .. Chlorine doesnt  show any change in presence of an indicator solution ;)

jus understand the concept ..


lol...Thanks alot ... but y does the indicator solution turns blue only at -ve electrodde and not the whole solution ?

Offline Vin

  • SF V.I.P
  • ********
  • Posts: 7914
  • Reputation: 52609
  • Gender: Male
    • Theory of Life - A new skew.
Re: Chemistry doubt
« Reply #16 on: May 24, 2010, 11:54:08 am »
lol...Thanks alot ... but y does the indicator solution turns blue only at -ve electrodde and not the whole solution ?

good ques .. see in this question u hav to act smart .. i think i forgot to mention .. look at the options .. u now kno tht NaOH is produced so the indicator turns blue ..there are two options with 'bule/purple' A and B .. now see A .. at -ve 'red' is given which is not possible because no acid it produced during the reaction so u r left with D .. ;)

Offline nerdvictim

  • Newbie
  • *
  • Posts: 18
  • Reputation: 28
Re: Chemistry doubt
« Reply #17 on: May 24, 2010, 03:21:36 pm »
hey, between which elements can you find carbon in the reactivity series ?!  ???

Offline Vin

  • SF V.I.P
  • ********
  • Posts: 7914
  • Reputation: 52609
  • Gender: Male
    • Theory of Life - A new skew.
Re: Chemistry doubt
« Reply #18 on: May 24, 2010, 03:23:38 pm »
hey, between which elements can you find carbon in the reactivity series ?!  ???


LEARN it ! ;)

Offline nerdvictim

  • Newbie
  • *
  • Posts: 18
  • Reputation: 28
Re: Chemistry doubt
« Reply #19 on: May 24, 2010, 03:32:26 pm »
LEARN it ! ;)

:P i sure will! thank you  ;D

Offline Vin

  • SF V.I.P
  • ********
  • Posts: 7914
  • Reputation: 52609
  • Gender: Male
    • Theory of Life - A new skew.
Re: Chemistry doubt
« Reply #20 on: May 24, 2010, 03:40:21 pm »
:P i sure will! thank you  ;D

sure .. ;) your welcome

Offline The Golden Girl =D

  • Without Allah I'm nothing <3
  • Honorary Member
  • SF Overlord
  • *****
  • Posts: 13757
  • Reputation: 65532
  • Ain't Nothin worth your tears =D
    • www.thegoldengirl157.blogspot.com
Re: Chemistry doubt
« Reply #21 on: May 24, 2010, 06:32:31 pm »
Ok remember when concentrated NaCl is electrolyzed:
First the solution contains Na+ Cl- and H+ and OH- (from water). The positive inos go to the cathode, and negative ions to the anode.

At the CATHODE
the H+ ions accept electrons, since it is less reactive than Na (always elements which is more reactive 'likes' to stay in the ionic form)
2H+  2e-  ---> H2

At the ANODE
the Cl- ions give up the electrons more readily than the OH- ions do.
2Cl-  -->  Cl2  +  2e-

what left in the solution is Na+ and OH- which combine to form NaOH

in your ques ..is 'D' .. the indicator solution turns blue at -ve as NaOH is produced .. Chlorine doesnt  show any change in presence of an indicator solution ;)

jus understand the concept ..



 u said H2 goes to cathode , then y u said sodium hydroxide changes indicator to blue when it is at the bottom not even close to the +ve electrode
Verily, in the remembrance of Allah do hearts find rest(13:28)

Please, Don't forget to Include GG in your Prayers =D

Offline Ghost Of Highbury

  • O_o_O lala!
  • SF Farseer
  • *******
  • Posts: 4096
  • Reputation: 41428
  • Gender: Male
  • Namaskaram!
Re: Chemistry doubt
« Reply #22 on: May 24, 2010, 06:41:15 pm »
Ok remember when concentrated NaCl is electrolyzed:
First the solution contains Na+ Cl- and H+ and OH- (from water). The positive inos go to the cathode, and negative ions to the anode.

At the CATHODE
the H+ ions accept electrons, since it is less reactive than Na (always elements which is more reactive 'likes' to stay in the ionic form)
2H+  2e-  ---> H2

At the ANODE
the Cl- ions give up the electrons more readily than the OH- ions do.
2Cl-  -->  Cl2  +  2e-

what left in the solution is Na+ and OH- which combine to form NaOH

in your ques ..is 'D' .. the indicator solution turns blue at -ve as NaOH is produced .. Chlorine doesnt  show any change in presence of an indicator solution ;)

jus understand the concept ..



it isnt concentrated, its aqueous .!!!
divine intervention!

Offline Vin

  • SF V.I.P
  • ********
  • Posts: 7914
  • Reputation: 52609
  • Gender: Male
    • Theory of Life - A new skew.
Re: Chemistry doubt
« Reply #23 on: May 24, 2010, 06:43:31 pm »
it isnt concentrated, its aqueous .!!!



AADI U GAVE ME AN ATTACK !! ITS CONCENTRATED AQ. NaCl
« Last Edit: May 24, 2010, 06:46:59 pm by ~VIN1094~ »

Offline 8T

  • SF Citizen
  • ***
  • Posts: 148
  • Reputation: 162
  • Gender: Female
Re: Chemistry doubt
« Reply #24 on: May 24, 2010, 06:50:01 pm »
hi By the way below copper theres mercury Hg
i have a question mj 04 p1 q 30
why is the answer C?
can sum1 explain plz
« Last Edit: May 24, 2010, 06:53:14 pm by 8T »
Know how to ask. There is nothing more difficult for some people, nor for others, easier.

Offline Ghost Of Highbury

  • O_o_O lala!
  • SF Farseer
  • *******
  • Posts: 4096
  • Reputation: 41428
  • Gender: Male
  • Namaskaram!
Re: Chemistry doubt
« Reply #25 on: May 24, 2010, 07:01:12 pm »
hi By the way below copper theres mercury Hg
i have a question mj 04 p1 q 30
why is the answer C?
can sum1 explain plz

the original is dilute NaOH because it has water in it...so say its pH is 10 (>7, because its alkali)

the distillate is water so pH = 7

the NaOH in the flask doesnt have any water left, so its concentrates that means its pH >10 (dilute NaOH)

thus , C
divine intervention!

Offline rhea

  • SF Immigrant
  • **
  • Posts: 66
  • Reputation: 82
Re: Chemistry doubt
« Reply #26 on: May 24, 2010, 07:05:05 pm »
hey can you tell me what colour chnages occur when universal indicator comes in contact with
hydrogen
oxygen
ammonia

and i thought acid /salt added to UI would not change the colour of UI.
right?

Offline 8T

  • SF Citizen
  • ***
  • Posts: 148
  • Reputation: 162
  • Gender: Female
Re: Chemistry doubt
« Reply #27 on: May 24, 2010, 07:16:47 pm »
UI in neutral solutions is green
in alkali blue if weak, violet if strong
in acid red & u do not test for gases with UI
Thanks A@di :)
Know how to ask. There is nothing more difficult for some people, nor for others, easier.

Offline Vin

  • SF V.I.P
  • ********
  • Posts: 7914
  • Reputation: 52609
  • Gender: Male
    • Theory of Life - A new skew.
Re: Chemistry doubt
« Reply #28 on: May 24, 2010, 07:17:12 pm »
hey can you tell me what colour chnages occur when universal indicator comes in contact with
hydrogen
oxygen
ammonia

and i thought acid /salt added to UI would not change the colour of UI.
right?


hydrogen - no change
oxygen - no change
ammonia - blue/purple

yes it does .. right click and click view image











Offline rhea

  • SF Immigrant
  • **
  • Posts: 66
  • Reputation: 82
Re: Chemistry doubt
« Reply #29 on: May 24, 2010, 07:25:17 pm »
hydrogen - no change
oxygen - no change
ammonia - blue/purple

yes it does .. right click and click view image












umm this means phenolphthalein is not an UI?