Chemistry: Post your doubts here!

[qwertypoiu]

Ik the answer is A but can someone tell me how the oxidation number of silver does not change? View attachment 59689

Oxidation state of Ag in AgCl: +1.
Oxidation state of Ag in [Ag(S2O3)2]3- : +1.

Note that S2O3 is 2- charge.

 

[holoholo]

Starting pH is 11.9 and final pH is 1.8. Vertical line is at 15cm^3.
Strong acid with weak base titration.
How do we label the endpoint ? At the start of the vertical line or at the end or at the middle ?

 

[holoholo]

Can someone please draw this fully labelled ?

 

[qwertypoiu]

View attachment 59727

Starting pH is 11.9 and final pH is 1.8. Vertical line is at 15cm^3.
Strong acid with weak base titration.
How do we label the endpoint ? At the start of the vertical line or at the end or at the middle ?

Middle is best

 

[qwertypoiu]

Can someone please draw this fully labelled ?

View attachment 59728

I think something like this should be good

 

[holoholo]

Middle is best

Isn't that the equivalence point ?

 

[holoholo]

Can someone please give me notes on the biochemistry part ?

 

[qwertypoiu]

Isn't that the equivalence point ?

I could be mistaken but I think the endpoint and the equivalence point is the same thing.

 

[alevelpleasebegood]

Can someone explain question 3iv) for me? I looked for the mark scheme but I couldn't understand it. http://studyguide.pk/Past Papers/CIE/International A And AS Level/9701 - Chemistry/9701_w07_qp_4.pdf

 

[The Sarcastic Retard]

Can someone explain question 3iv) for me? I looked for the mark scheme but I couldn't understand it. http://studyguide.pk/Past Papers/CIE/International A And AS Level/9701 - Chemistry/9701_w07_qp_4.pdf

As potential value of Cr2O7(2-)/Cr(3+) is more than Br2/Br(-) So Cr(VI) would oxidise Br- to Br2 easily.

 

[Saad the Paki]

Thank you so much qwertypoiu

 

[holoholo]

For solution C, I wrote [Cu(NH3)4(H2O)2]SO4^2-

But in the mark scheme it is

Can you please explain ?

 

[qwertypoiu]

View attachment 59735

For solution C, I wrote [Cu(NH3)4(H2O)2]SO4^2-

But in the mark scheme it is View attachment 59736

Can you please explain ?

They specifically mentioned ANHYDROUS copper sulphate, dissolved in LIQUID ammonia at -33degrees.

There can be no justification for including H2O molecules in your answer; where can H2O possibly come from? There is no water involved here.
Since Cu2+ has coordination number of 6, the examiner expects the students to realise that 6 molecules of NH3 will form coordinate bonds with the central Cu2+ ion.

 

[holoholo]

Do we have to know what affects the enzymes like pH temperature etc ? What exactly do we have to know about enzymes because i can't seem to understand it from the syllabus ?

 

[holoholo]

Explanation please ?

 

[qwertypoiu]

View attachment 59746

Explanation please ?

White light is made up of ROYGBIV

Since they said the ion absorbs red and violet regions of the visible light, the GREEN in the middle is left to be reflected into your eyes.

 

[Eugene99]

White light is made up of ROYGBIV

Since they said the ion absorbs red and violet regions of the visible light, the GREEN in the middle is left to be reflected into your eyes.

Your explanations are awesome!

 

[qwertypoiu]

Your explanations are awesome!

Thank you so much it means a lot

 

[Abdullahassan_99]

Can someone plz tell me the answer to this question with its explanation?

 

[qwertypoiu]

Can someone plz tell me the answer to this question with its explanation?View attachment 59756

First write the Kc expression for this reaction:
Kc = [HI]^2 / [I2]*[H2]

We know Kc = 60 at the specified temperature.

Assume a container of 1dm^3 for simplicity:
[H2] = 2
[I2] = 0.3
Kc = 60
[HI] = sqrt(Kc*[I2]*[H2]) = sqrt(60*0.3*2) = sqrt(36) = 6mol/dm^3