Chemistry: Post your doubts here!

[wolfestein99x]

31 The 1 H3 + ion was first characterised by J. J. Thomson over a century ago. 6 Li is a rare isotope of lithium which forms the 6 Li+ ion.
Which statements are correct?
1 Both ions contain the same number of protons.
2 Both ions contain the same number of electrons.
3Both ions contain the same number of neutrons.

ans is b explainnn

amina1300 its a H3 molecule thats lost an electron , how many portons does it have (1 x 3 = 3 protons) and hence how many electrons (3 - 1 = 2) and no neutrons.
next one is 6Li molecule thats also lost an elctron , how many portons does it have (look up the periodic table 3 protons) and hence how many electrons (3 - 1 = 2).

 

[wolfestein99x]

Which reaction will give 2-chloropropane in the best yield?
A chlorine gas with propene gas in the presence of UV light
B cl2 gas with propene gas in the dark
C propan-2-ol with dil NaCl
D propan-2-ol with PCl5
The answer is D can anyone explain??

amina1300 lol i think D is the only reaaction that can produce 2 chloro propane XD , C is just alcohol and salt . A and B proudce dichloro propane

 

[wolfestein99x]

Help! Can somebody plz explain me question 33

Laveeza whats the answer , C ? 2 and 3 are certainly true thats easy to understand right . 1 says there will be pressure difference between the atmosspere and the syringe rigth ? the reaction is in equilibrium/volume is constant/pressure is contant. Now if the pressure in the syringe was more it would increase the volume of the syringe gettit ? the syringe would decompress and the pressure will decrease back to atmospheric pressure . hence at equilibrium the pressure is same on bath sides. Confirm the ans pliss is it C ?

 

[wolfestein99x]

Option D is only correct. i.e.
1 Aluminium is oxidised. (only)
why
If we look at the oxidation state of Al than we can clearly see that Al is oxidised from 0 to +3
while chlorine's oxidation state remains the same.i.e. -1
And Nitrogen is reduced from +5 to 0 while statement 3 says the opposite.
so answer is D

Hope it helped.

Hey yo sherlock the answer is A , ya didnt help much XD

 

[techgeek]

View attachment 62065
can anyone plzz explain this qtns...
thanks in advance

NaOH + CH3CO2H ----------- CH3CO2Na + H2O
moles of NaOH= C*V = 10/1000 * 0.100 = 0.001 moles of acid= C*V = 10/1000 * 0.250 = 0.0025
Hence acid is excess. Both will react with 1 ratio 1 so acid remaining would be 0.0025-0.001= 0.0015 moles.
The moles of salt would be 0.001 as moles of CH3CO2Na are 0.001.
Then you will calculate concentrations of both salt and acid. Total volume, now, is 20 cm3. Use the formula C=n/V to calculate concentrations.
Then use pH= pKa + log(salt/acid)

 

[areeba240]

this is how its done not sure if its right tho , do share the ans

the ans is correct .........but why are u taking the final volume as 20..??

 

[wolfestein99x]

the ans is correct .........but why are u taking the final volume as 20..??

We always take the total volume of the buffer solution when calculating conc of acid or salt , in most cases they have already given the conc of salt and acid .

 

[techgeek]

the ans is correct .........but why are u taking the final volume as 20..??

We always take the total volume of the buffer solution when calculating conc of acid or salt , in most cases they have already given the conc of salt and acid .

why not 20?
Looking at it practically, adding 10 cm^3 of acid to 10 cm^3 of alkali would result in a total volume of 20.. no?
The amount of acid though changed because some of the moles reacted with alkali to give a salt, but it has whatsoever nothing to do with volume, the concentration changes because of the moles of solute present.

 

[wolfestein99x]

why not 20?
Looking at it practically, adding 10 cm^3 of acid to 10 cm^3 of alkali would result in a total volume of 20.. no?
The amount of acid though changed because some of the moles reacted with alkali to give a salt, but it has whatsoever nothing to do with volume, the concentration changes because of the moles of solute present.

The volume is not.to.be ignored , its not affecting anything but it is there , well if you do look at it practically, the volume.wouldnt be 20cm3 u gotta take into account the H20 formed when NaOH ions react with the salt thats why i was worried about the ans , we completely ignore the water formed.but then again the volume would still be the same so that is stupid to think about XD

 

[techgeek]

The volume is not.to.be ignored , its not affecting anything but it is there , well if you do look at it practically, the volume.wouldnt be 20cm3 u gotta take into account the H20 formed when NaOH ions react with the salt thats why i was worried about the ans , we completely ignore the water formed.but then again the volume would still be the same so that is stupid to think about XD

water formed is in liquid state too.. so total volume of products remain the same

 

[wolfestein99x]

water formed is in liquid state too.. so total volume of products remain the same

Yeah no shit sherlock , i mentioned that i think ^

 

[student2]

its simple if you look at H the order is CH3 then H the OH think of this as a loop , you can go from ch3 to H but not directly to OH.
Now look at J the order is OH , H and then CH3 is that not different student2 ?its the opposite actually u have to imagine the structure in 3d , btw the ans is J ?

yh its J. thnx fr ur tym

 

[shingiechingz@8]

did any wrote 9701/M/J/21/2017

 

[TRAMANZ]

did any wrote 9701/M/J/21/2017

I did

 

[shingiechingz@8]

I did

How was it......to me it was pretty much tooo easy

 

[MarcosT200]

How was it......to me it was pretty much tooo easy

Hey I did the same one!

I got the first question completely wrong since i didn't get the correct values for x and y, but do you think they will give error carried forawerd marks in the following ones? Because I didn't use the x=4 and y=10 since I thought I had the values correct. I got 6 and 16, which make nl sense!

For the one on lattices and all that, what type of lattice is ice? And the bonding between iodine?

 

[shingiechingz@8]

Hey I did the same one!

I got the first question completely wrong since i didn't get the correct values for x and y, but do you think they will give error carried forawerd marks in the following ones? Because I didn't use the x=4 and y=10 since I thought I had the values correct. I got 6 and 16, which make nl sense!

For the one on lattices and all that, what type of lattice is ice? And the bonding between iodine?

i they will probably give u ecf marks . the values i got were x=3 and y=8 .Double your answers haha and as for lattice for ice i wrote crystal and bonding for ice covalent

 

[TRAMANZ]

It was pretty calm. I was so glad Enthalpy didnt come, Organic was soo calm. I am sure paper 4 is gonna be deadly. All the best guys!!

 

[msucurt]

thanks so much!

 

[msucurt]

Could someone please help with a calculation from Paper 3 (may/june_2009). Its the calculations portion of question #1. Ive attached my work. The question is a titration of borax vs HCl.

• I am having difficulty understanding where the .008moles HCl come from on the mark scheme on #1c(i).
• I am having difficulty understanding why the Mr is so large from my calculations on #1c(iv)

thanks!!