Chemistry: Post your doubts here!

[selrey]

it went gr8
tho lost one mark in q2 last part
rest was all okay

My q1 n q3 went okay Alhamdulillah but i ran out of time so i couldnt really finish q2. I really hope i get marks in 30's thou xD

 

[anastasia grey113]

My q1 n q3 went okay Alhamdulillah but i ran out of time so i couldnt really finish q2. I really hope i get marks in 30's thou xD

dw
if ur theory went good itll be fine

 

[Minahil rizvi]

https://papers.gceguide.xyz/A Levels/Chemistry (9701)/9701_s05_qp_1.pdf
Q36 guys, help'''''

 

[Farjad Ilyas]

https://papers.gceguide.xyz/A Levels/Chemistry (9701)/9701_s05_qp_1.pdf
Q36 guys, help'''''

1. Cl2 + Mg ---> MgCl2 and 1/2 Cl2 + Na ---> NaCl
Chlorine reacts with Mg to form MgCl2 bu reacts with Na to form NaCl. So twice the number of moles of Cl react with Mg (X) compared to Na (Y). This option is correct.

2. Again, Cl2 reacts with H2 to form 2HCl: Cl2 + H2 ---> 2HCl
and Chlorine displaces Br in KBr: 1/2 Cl + KBr ---> KCl + HBr
So twice the no of moles of Cl2 react with H2 compared to Kbr. So this option is also correct

3. Cl2 + 2NaOH ---> NaCl +NaCLO + H2O
3Cl2 +6 NaOH ---> 5NaCl + NaClO3 + 3H2O
In both of these reactions, Cl2 and NaOH react in the ratio 1:2. So the number of moles of Cl2 that react with 1 mol of X isn't twice the number of moles that react with Y. So this option is wrong. The ans is B

 

[Minahil rizvi]

1. Cl2 + Mg ---> MgCl2 and 1/2 Cl2 + Na ---> NaCl
Chlorine reacts with Mg to form MgCl2 bu reacts with Na to form NaCl. So twice the number of moles of Cl react with Mg (X) compared to Na (Y). This option is correct.

2. Again, Cl2 reacts with H2 to form 2HCl: Cl2 + H2 ---> 2HCl
and Chlorine displaces Br in KBr: 1/2 Cl + KBr ---> KCl + HBr
So twice the no of moles of Cl2 react with H2 compared to Kbr. So this option is also correct

3. Cl2 + 2NaOH ---> NaCl +NaCLO + H2O
3Cl2 +6 NaOH ---> 5NaCl + NaClO3 + 3H2O
In both of these reactions, Cl2 and NaOH react in the ratio 1:2. So the number of moles of Cl2 that react with 1 mol of X isn't twice the number of moles that react with Y. So this option is wrong. The ans is B

Thankyou got it

 

[shahzaib ihsan]

a problem:
The compound pentan-1,4-diol has two OH groups per molecule and can be oxidised.
Which statements about pentan-1,4-diol or its oxidation products are correct?
1. When one mole of pentan-1,4-diol reacts with an excess of sodium metal, one mole of hydrogen molecules is produced.
2. At least one of the possible oxidation products of pentan-1,4-diol will react with 2,4-dinitrophenylhydrazine reagent.
3. Dehydration of pentan-1,4-diol could produce a compound with empirical formula C5H8.

which statement(s) is/are correct?
may/june 2014, variant 11 question 39.

 

[anastasia grey113]

a problem:
The compound pentan-1,4-diol has two OH groups per molecule and can be oxidised.
Which statements about pentan-1,4-diol or its oxidation products are correct?
1. When one mole of pentan-1,4-diol reacts with an excess of sodium metal, one mole of hydrogen molecules is produced.
2. At least one of the possible oxidation products of pentan-1,4-diol will react with 2,4-dinitrophenylhydrazine reagent.
3. Dehydration of pentan-1,4-diol could produce a compound with empirical formula C5H8.

which statement(s) is/are correct?
may/june 2014, variant 11 question 39.

all 3 r correct i think

 

[Minahil rizvi]

How many different substitution products are possible, in principle, when a mixture of bromine and ethane is allowed to react?
A 3 B 5 C 7 D 9

 

[furuta]

hello~
can someone please solve the following problem for me?

1. Use of the Data Booklet is relevant to this question.
   The gas laws can be summarised in the ideal gas equation.
   
   pV = nRT
   0.96 g of oxygen gas is contained in a glass vessel of volume 7000 cm3 at a temperature of 30 °C.
   
   What is the pressure in the vessel?
   A 1.1kPa B 2.1kPa C 10.8kPa D 21.6kPa
   
   thank you x

 

[SohaibButt]

hello~
can someone please solve the following problem for me?

1. Use of the Data Booklet is relevant to this question.
   The gas laws can be summarised in the ideal gas equation.
   
   pV = nRT
   0.96 g of oxygen gas is contained in a glass vessel of volume 7000 cm3 at a temperature of 30 °C.
   
   What is the pressure in the vessel?
   A 1.1kPa B 2.1kPa C 10.8kPa D 21.6kPa
   
   thank you x

P×7000×10*-6=0.96/32×8.31×303


Ans:10.8 kPa

So it's C

 

[shahzaib ihsan]

all 3 r correct i think

my question still remains unsolved as i need a detailed explanation regarding why all 3 are correct..

 

[furuta]

P×7000×10*-6=0.96/32×8.31×303


Ans:10.8 kPa

So it's C

oh right i accidentally took 16 as the mr instead of 32 alright thank you

 

[techgeek]

my question still remains unsolved as i need a detailed explanation regarding why all 3 are correct..

 

[shahzaib ihsan]

View attachment 62265

Thank you so much!

 

[Shaaaazxx]

Perhaps you can list down the other option(s) you thought were also correct, then we can guide you accordingly.

We can try replacing option A (correct answer) with something familiar

CH4 (g) --> C (g) + 4 H (g) ∆H

Bond energy of C-H is ∆H/4
1/4 CH4 (g) --> 1/4C (g) + H (g)

H4 (g) --> C (g) + 4 H (g) ∆H

Analogously
XYn (g) --> X (g) + n Y (g) ∆H

Bond energy of X-Y is ∆H/n
1/n XYn (g) --> 1/n X (g) + Y (g) ∆H

Thankyou soo muchh!! <33

 

[shahzaib ihsan]

K2O + H2SO4 ----> K2SO4 + H2O
Moles of acid = 15/1000*2 = 0.03mol
Moles of K2O in 25cm3 = 0.03mol, due to ratio.
Moles of K2O in 250cm3, = 0.03*10 = 0.3mol
Mass = (39.1*2+16)*0.3 = 28.26g

this question: October/November 2014 variant 12 question number 15.
the equation: K2O + H2SO4 ---> K2SO4 + H2O i don't think this is correct as the question said that K2O is dissolved in water.
so i think these 2 equations may be used to solve the question:
1) K2O + H2O ---> 2KOH
2) 2KOH + H2SO4 ---> K2SO4 + 2H2O.
but i can't seem to find the answer. However i found this on yahoo answers:

(2 mol/dm^3 H2SO4) x (0.015 dm^3) x (2 mol KOH / 1 mol H2SO4) x (1 mol K2O / 2 mol KOH) x
(250 cm^3 / 25 cm^3) x (94.1960 g K2O/mol) = 28 g K2O

can anyone explain this to me on plain paper and/or step by step?

 

[Minahil rizvi]

g

How many different substitution products are possible, in principle, when a mixture of bromine and ethane is allowed to react?
A 3 B 5 C 7 D 9

guyssss help me with this

 

[techgeek]

g

guyssss help me with this

there are 9?

 

[techgeek]

g

guyssss help me with this

When ethane reacts with Bromine, it forms CH2BrCH3 but the product can react with Br2 again and form disubstituted product which reacts again with Br2 and form trisbustituted product and so on, we can actually form even hexasubstituted product. So it goes like this:
Monosubstituted:
CH2BrCH3
Disubstituted:
CH2BrCH2Br
and
CHBr2CH3
Trisubstituted:
CH3CBr3
and
CHBr2CH2Br
Tetrasubstituted:
CBr3CH2Br
and
CHbr2CHBr2
Pentasubstituted:
CBr3CHBr2
Hexasubstituted:
CBr3CBr3

 

[DeadbeatCIE]

How does one prove if a reaction is a first order process or not using graph?
What is a first order process?
What are half lives and how do i draw half life lines?
I fear this might come in the practical
Help me out here