Chemistry: Post your doubts here!

[robinhoodmustafa]

why is A the right answer?
why would C decolourise AQueous BRomine?
Haven't we learnt that only alkene ( out of all the homologous series) decolourises aq bromine and it is a universal test for alkene as well:/

Question says "Will NOT de-colorized bromine..

Does Chlorine overtake Bromine gas O-o? strange!

 

[Bba321]

Bcz in the question its clearly given that the final colour of the solution is Blue which means , at the end we are left up with fe+2....definately then we'll use the equ in which iron +3 will reduce to iron +2 rather then using the other equ....
Hope you have got it ..ryt!

Isn't the colour of Fe 2+ green?

 

[Hassan Ali Abid]

Isn't the colour of Fe 2+ green?

when one will reduce the other will oxidise so cu+ will oxidise to +2..ie cu+ ----> cu+2 which is responsible for the blue colour ...

 

[Bba321]

when one will reduce the other will oxidise so cu+ will oxidise to +2..ie cu+ ----> cu+2 which is responsible for the blue colour ...

Ohh tnx

 

[Excellence]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_2.pdf

Question 2c

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_2.pdf

Question 2c

Kc=[Products]^n/[Reactants]^n
Kc is only affected by temperature temperature in the question is the same and therefore the value of kc is the same.
Suppose x moles of ethanoic acid have been used up at equilibrium. The number of moles of ethanoic acid left will be 0.5-x.For every mole of ethanoic acid that is used up, the same number of moles of ethanol will have gone, because they react 1 to 1. There will be 1.0 - x moles of ethanol left as well. For each mole of ethanoic acid that gets used up 1 mole of ethyl ethanoate and 1 mole of water are formed. So if x moles of ethanoic acid are used up, x moles of ethyl ethanoate and x moles of water will be formed but be careful we already have initial moles of both products,add them up.
now use the expression above.
Kc=[CH3CH2CO2C2H5][H2O]/[CH3COOH][C2H5OH]=[0.1+x/v]^2/[0.5-x/v]^2=4 V cancels out and take the square root of both sides.
o.1+x/0.5-x=2 2(0.5-x)=(0.1+x) 1-2x=0.1+x 3x=0.9 x=0.3
0.1+0.3=0.4
0.5-0.3=0.2

 

[Farhad221]

Salam ,
Can someone help me with this question.

 

[saman sabir]

hi everyone...can anyone tell me how do i prepare for chemistry olevels?

 

[Abdel Moniem]

Salam ,
Can someone help me with this question.View attachment 50809

In ClO3-the sum of oxidatio numbers in an ion is equal to the charge on the ion which is -1. The more electronegative element is given the negative oxidation number which is in this case oxygen.we have got 3 O atoms so their oxidation number is -2*3=-6 and Cl is +5 in order to correspond to the overall charge of the whole ion. SO2 has its sum of oxidation number equal to zero. O has an oxidation number of -2*2=-4 and sulphur's oxidation number is +4. ClO2 compound has its sum of oxidation equal to zero again. There are 2 O atoms present so their oxidation numbers are -2*2=-4 and so Cl has an oxidation number of +4. SO4^-2 ion has an overall oxidation of -2 so Sulpur must have an oxidation number equal to 6 to cope with the overall.

 

[Paris Palmer]

In hydrogen magnetic resonance spectrometry, when an atom is placed in an external magnetic field, the electron pairs spin in such a manner to produce a magnetic field opposing external magnetic field. S o both fields are cancelled out and the protons inside the nucleus are shielded. Now that external field has been cancelled out, will the nucleus continue to spin the way it was spinning before being placed in the field?

 

[Paris Palmer]

Can someone please explain what exactly is chemical shift?

 

[♣♠ Magnanimous ♣♠]

hi everyone...can anyone tell me how do i prepare for chemistry olevels?

Read your book thoroughly and after solve past papers and if any doubt post it here

 

[Abdel Moniem]

In hydrogen magnetic resonance spectrometry, when an atom is placed in an external magnetic field, the electron pairs spin in such a manner to produce a magnetic field opposing external magnetic field. S o both fields are cancelled out and the protons inside the nucleus are shielded. Now that external field has been cancelled out, will the nucleus continue to spin the way it was spinning before being placed in the field?

It is important to remember that with NMR, we are applying an external magnetic field to the nuclei of the atom not to the electrons.

 

[Sarosh Jameel]

Please help with june 2005 p1 .. q1 ... ASAP!

 

[danial 234]

Please help with june 2005 p1 .. q1 ... ASAP!

Ans C)
10 cm3 of hydrocarbon produced 30 cm3 of CO2..
so the ratio tells that there were 3 carbons in one molecule of hydrocarbon.. this narrows your options to B and C.
We know that one mole of O2 reacts with one mole of carbon.Now, out of the 50cm3 of O2 which took part in the reaction, 30 cm3 reacted with Carbon to form CO2.
The remaining 20 cm3 reacted with hydrogen. Also, 1 mole of O2 reacts with 2 moles of Hydrogen to form 2 moles of water, so 2o cm3 of O2 would have required 40 cm3 of H2 . There must be 8 atoms of hydrogen in one molecule.
So the formula of the hydrocarbon is C3H8.

 

[Sarosh Jameel]

Thanks !!

Ans C)
10 cm3 of hydrocarbon produced 30 cm3 of CO2..
so the ratio tells that there were 3 carbons in one molecule of hydrocarbon.. this narrows your options to B and C.
We know that one mole of O2 reacts with one mole of carbon.Now, out of the 50cm3 of O2 which took part in the reaction, 30 cm3 reacted with Carbon to form CO2.
The remaining 20 cm3 reacted with hydrogen. Also, 1 mole of O2 reacts with 2 moles of Hydrogen to form 2 moles of water, so 2o cm3 of O2 would have required 40 cm3 of H2 . There must be 8 atoms of hydrogen in one molecule.
So the formula of the hydrocarbon is C3H8.

THANKS !

 

[princess Anu]

how is it reduction
CrO2Cl2 ---> Cr2O3?

Cl has a oxidation state of +1 or -1 ?

 

[danial 234]

how is it reduction
CrO2Cl2 ---> Cr2O3?

Cl has a oxidation state of +1 or -1 ?

In the reactant,
Cr has an oxidation state of +6 and oxygen has an oxidation state of -2. And chlorine has an oxidation state of -1.
In the product, Cr has an oxidation state of +3. So Cr+6 has been reduced to Cr+3.

 

[princess Anu]

how does hydrogen bonding in water explains why ice floats on water?

Can someone solve me mj 2010/11 MCQ 18,20,27
pleaseee

 

[♣♠ Magnanimous ♣♠]

how does hydrogen bonding in water explains why ice floats on water?

Can someone solve me mj 2010/11 MCQ 18,20,27
pleaseee

In solid ice hydrogen bonding give rise to an open cage like structure in with each water molecule is linked tetrahedrally to four molecules. Thus molecules no longer remain closely packed and mass per unit volume i.e. density decreases. That is why ice floats on water.