Physics, Chemistry and Biology: Post your doubts here!

[Zubair Junjunia]

Why does acidified KMnO4 turn colorless in alkenes?

Potassium Manganate is a oxidising agent therefore is reduced itself. As alkenes are unsaturated, they are able to react with the MnO4 ion and that is why it turns colourless

 

[Gamedos]

here u go , Q3

as the water is starting 2 evaporate so energy is used to weaken bonds instead of increasing temp

 

[Gamedos]

Why does acidified KMnO4 turn colorless in alkenes?

alkenes are reducing agents

 

[Gamedos]

here u go , Q3

and by the way,from where did u get this paper 3 revision sheet

 

[princess sofia]

and by the way,from where did u get this paper 3 revision sheet

from some thread on xpc , dnt rememebr

 

[Emadthegreat]

no doubts

 

[eureka!]

Describe the action of heat ( if any) on :

1) Hydroxides of Ca, Cu, Fe, Mg, K, Na, Zn
2) Nitrates of Ca, Cu, Fe, Mg, K, Na, Zn


Awesome12 eureka!

Hydroxides:
•KOH, NaOH UNchanged.
•The rest: hydroxide + heat ---> oxide + water
e.g. Ca(OH)^2 ∆---> CaO + H2O;
2Fe(OH)3 ∆---> Fe2O3 + 3H2O

Nitrates:
•NaNO3, KNO3: nitrate + heat ---> nitrite + oxygen
e.g. 2NaNO3 ∆---> 2NaNO2 + O2
•The rest: nitrate + heat ---> oxide + nitride + oxygen
e.g. 2Ca(NO3)2 ∆---> 2CaO + 4NO2 +O2
2Fe(NO3)2 ∆---> 2FeO + 4NO2 + O2

 

[Emadthegreat]

thanks

 

[princess sofia]

how is it C shdnt it b A

 

[loaie Amgad]

how is it C shdnt it b A View attachment 42765

I was Just solving this paper
Got 39/40
Just because of this strange question
Well , I think that we should understand the way the plastic supports the metal case

 

[Zubair Junjunia]

how is it C shdnt it b A View attachment 42765

From the diagram, it appears that the metal case does not go back to the beginning so that means current wouldn't flow after it reaches the cable so its not a full circuit. Ofcourse, u can argue otherwise however u must remember that CIE is looking for the "most suitable answer" so the most plausible answer in those options is that someone will receive a shock because as soon as he touches it, the circuit is complete.

 

[DarkEclipse]

Why does acidified KMnO4 turn colorless in alkenes?

Because KMnO4 is a good oxidizing agent. It's not your average good oxidizing agent, but a super one. It breaks the double bond present in alkenes, which allows them to form more bonds with other elements. The oxygen molecules from KMnO4, since there are a total of 4, they move on to the alkene, and 2 are added to either side.
Now, KMnO4 has no more oxygen molecules left. Due to this, it loses its prominent purple color.
The mechanisms of this reaction is really complex and not present in our level, but this is the general idea.

 

[xlnc123]

CHEM DOUBT PAPER 3
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s12_qp_31.pdf
QUESTION 8 part 2

 

[hard_worker]

I was Just solving this paper
Got 39/40
Just because of this strange question
Well , I think that we should understand the way the plastic supports the metal case

omg WOW i usually get between 25-29 out of 40 in solving these papers..... I see many physics geniuses out there ..so high curvesss nooooo

 

[princess sofia]

omg WOW i usually get between 25-29 out of 40 in solving these papers..... I see many physics geniuses out there ..so high curvesss nooooo

lol , i also scored 35 , worst paper

 

[Faiza Anwar]

Assalam-o-Alaikum.
Post your Physics, Chemistry and Biology doubts in here and members, along with me will try their best to help you out.

in chem M/J 2011 p32 Q 8a(iv) how can we know the moles of water???

 

[Faiza Anwar]

A very simple question from me... What is the difference between evaporation and crystallisation... What does one method offer that the other does not? I'm posing this question because both methods of separation seem to satisfy the same objective: extracting a dissolved substance from a solution...

we evaporate to remove the liquid completely which would form anhydrous crystals, while in crystallisation we don't remove the water r crystallisation nd obtain hydrated crystals.....

 

[salma mohd]

is there any one who is online asap !!
i have a very important thing regarding physics

 

[Faizan Muhammmad]

yes?

 

[Faiza Anwar]

yes!