Chemistry: Post your doubts here!

[My Name]

Answer is C

 

[Metanoia]

There are four geometrical isomers. Remember that there are TWO double bonds in the structure, and both are able to have geometrical isomerism. It is difficult to draw them, but imagine this:

FIRST DOUBLE BOND...........SECOND DOUBLE BOND.......
1). cis..........................................cis.................
2). cis........................................trans.................
3). trans......................................cis...........................
4). trans....................................trans...........................


Therefore, there are 4 isomers. In general, if there are x double bonds in a compound that are able to show cis-trans isomerism, there are 2^x geometric isomers of the compound. (eg if there are 3 double bonds, 8 isomers will be seen.)

You need to subtract 1 isomer in this question as its a symmetrical molecule. The cis-trans and trans- cis are identical.

 

[Metanoia]

Answer is C

The cold dilute KMnO4 adds 2 OH across the C=C bonds, the original OH on the bottom not oxidised to a ketone as it is not heated. So there will be 3 OH in the product.

The hot KMnO4 cleaves the C=C bonds, you have only the bottom and 3rd from bottom rings with 6 carbons.

 

[naughty11]

can someone tell me where to find the recent papers? i mean june and nov 2014.

thank you.

 

[Metanoia]

can someone tell me where to find the recent papers? i mean june and nov 2014.

thank you.

http://onlineexamhelp.com/past-pape...-as-level/9701-chemistry-a-as-level-year-wise

 

[qwertypoiu]

You need to subtract 1 isomer in this question as its a symmetrical molecule. The cis-trans and trans- cis are identical.

Yeah sorry, you're right. I've edited my answer now.

 

[qwertypoiu]

The answer is B for that questions .. sorry maybe u might haven't noticed it ... :/

fixed it now thanks.

 

[qwertypoiu]

The part on the cis-trans is incorrect. We are talking of cycloalkenes, for ring structures less than 8 carbons, we will not expect to see the trans isomer due to the strain on the bonds.

Thanks.

 

[The Sarcastic Retard]

http://maxpapers.com/wp-content/uploads/2012/11/9701_w14_qp_12.pdf
Q4
Q6
Q15
Q16
Q17
Q30 to Q36

 

[shazmina]

There are four geometrical isomers. Remember that there are TWO double bonds in the structure, and both are able to have geometrical isomerism. It is difficult to draw them, but imagine this:

FIRST DOUBLE BOND...........SECOND DOUBLE BOND.......
1). cis..........................................cis.................
2). cis........................................trans.................
3). trans......................................cis...........................
4). trans....................................trans...........................


Therefore, there are 4 isomers. In general, if there are x double bonds in a compound that are able to show cis-trans isomerism, there are 2^x geometric isomers of the compound. (eg if there are 3 double bonds, 8 isomers will be seen.)


EDIT: Sorry, it should be three, as cis,trans and trans,cis will be the same, just flipped around; due to this compound's symmetry.

Thanks alot brother Very comprehensible

 

[Ahmed Aqdam]

http://maxpapers.com/wp-content/uploads/2012/11/9701_w14_qp_12.pdf
Q4
Q6
Q15
Q16
Q17
Q30 to Q36

4. PV/T is equal before and after the valve is opened.
Temperature is taken in Kelvins. Volume is taken at V before valve is opened. Total volume after is 4V after valve is opened.
1*10^5*V/(20+273)=P*(4V)/(100+273)
Solve to get 3.18*10^4.

6. Al4C3+NaOH+H2O----->NaAlO2+hydrocarbon
Al has 4 atoms so there are 4 moles of NaAlO2 to balance the equation and hence 4 moles of NaOH too. Now there are 8 oxygen atoms in products but only 4 in reactants so 4 more are needed from H2O to balance. This makes 3 C atoms and 12 H atoms. Only CH4 has 4 times Hydrogen atoms as Carbon does.
Al4C3+4NaOH+4H2O----->4NaAlO2+3CH4

15. K2O+H2SO4 so both react in 1:1 ratio.
Moles of H2SO4: 2*15/1000=0.03
Moles of K2O in 250 cm^3=0.03*250/25=0.3
Mr of K2O=94.2
Mass=94.2*0.3=28.3g

16. In cold NaClO is produced. Na is +1, O is -2 so Cl must be +1.
In hot NaClO3 is produced. Na is +1, O is -6 when added so Cl is +5.
NaCl is also produced in both reactions and Cl is -1 in this.

17. Br2 will not react with Cl- as it is less reactive.
Cl2 will displace Br-. This will be oxidation as Br will become 0 from -1.

 

[Xylferion]

4. PV/T is equal before and after the valve is opened.
Temperature is taken in Kelvins. Volume is taken at V before valve is opened. Total volume after is 4V after valve is opened.
1*10^5*V/(20+273)=P*(4V)/(100+273)
Solve to get 3.18*10^4.

6. Al4C3+NaOH+H2O----->NaAlO2+hydrocarbon
Al has 4 atoms so there are 4 moles of NaAlO2 to balance the equation and hence 4 moles of NaOH too. Now there are 8 oxygen atoms in products but only 4 in reactants so 4 more are needed from H2O to balance. This makes 3 C atoms and 12 H atoms. Only CH4 has 4 times Hydrogen atoms as Carbon does.
Al4C3+4NaOH+4H2O----->4NaAlO2+3CH4

15. K2O+H2SO4 so both react in 1:1 ratio.
Moles of H2SO4: 2*15/1000=0.03
Moles of K2O in 250 cm^3=0.03*250/25=0.3
Mr of K2O=94.2
Mass=94.2*0.3=28.3g

16. In cold NaClO is produced. Na is +1, O is -2 so Cl must be +1.
In hot NaClO3 is produced. Na is +1, O is -6 when added so Cl is +5.
NaCl is also produced in both reactions and Cl is -1 in this.

17. Br2 will not react with Cl- as it is less reactive.
Cl2 will displace Br-. This will be oxidation as Br will become 0 from -1.

For 15, how do you figure out the ratio? How did you know it's 1:1?

 

[Turki AbdulAziz]

http://freeexampapers.com/A-Level/Chemistry/CIE/2007-Jun/9701_s07_qp_1.pdf
I need help in q) 9 , 12 and 13

 

[qwertypoiu]

For 15, how do you figure out the ratio? How did you know it's 1:1?

Try writing the full equation and balancing it. Metal oxides react with acids to form a salt and water:
K2O + H2SO4 ---> K2SO4 + H2O.
This equation needs no balancing, and you can see therefore that the ratio of all the species is 1:1:1:1

 

[qwertypoiu]

http://freeexampapers.com/A-Level/Chemistry/CIE/2007-Jun/9701_s07_qp_1.pdf
I need help in q) 9 , 12 and 13

9). Write Kc expression for both, and you'll see that the Kc for reaction 2 is the inverse and square root of the reaction 1 Kc, so the answer is 1/sqrt(2)
12) AlCl3, is a well known compound in our syllabus with slight ionic and slight covalency, and accounts for its amphoteric nature.
13) The Al is bonded to 4 stuff, and so they must be bonded tetrahedrally, so D.

 

[Xylferion]

Try writing the full equation and balancing it. Metal oxides react with acids to form a salt and water:
K2O + H2SO4 ---> K2SO4 + H2O.
This equation needs no balancing, and you can see therefore that the ratio of all the species is 1:1:1:1

Thanks

 

[Turki AbdulAziz]

9). Write Kc expression for both, and you'll see that the Kc for reaction 2 is the inverse and square root of the reaction 1 Kc, so the answer is 1/sqrt(2)
12) AlCl3, is a well known compound in our syllabus with slight ionic and slight covalency, and accounts for its amphoteric nature.
13) The Al is bonded to 4 stuff, and so they must be bonded tetrahedrally, so D.

Thanks a lot!
I understood 9 and 13, but for 12 I also thought it was AlCl3 until I checked the mark sheme which gave the correct answer as MgCl2

 

[qwertypoiu]

Thanks a lot!
I understood 9 and 13, but for 12 I also thought it was AlCl3 until I checked the mark sheme which gave the correct answer as MgCl2

Sorry my bad.
The question says: "Which chlorine compound has bonding that can be described as ionic with some covalent character?"
AlCl3 is actually a covalent compound, it's NOT ionic. I was getting confused by Aluminium OXIDE, which reacts with both acids and bases and is amphoteric.
NaCl when dissolved in water forms a solution with pH of 7. It forms Na+ ions and Cl- ions. It is completely ionic. AlCl3, being covalent (and not ionic), hydrolyses in water and forms Al(OH)3 and HCl. The resulting solution has a pH of 3.
MgCl2 can be described as ionic but forms a solution with pH of 6.5 when dissolved in water. The slight acidity is attributed to the slight covalent character.
So again, AlCl3 cannot be described as ionic, rather it is a covalent compound. So the right answer is MgCl2

 

[Turki AbdulAziz]

Sorry my bad.
The question says: "Which chlorine compound has bonding that can be described as ionic with some covalent character?"
AlCl3 is actually a covalent compound, it's NOT ionic. I was getting confused by Aluminium OXIDE, which reacts with both acids and bases and is amphoteric.
NaCl when dissolved in water forms a solution with pH of 7. It forms Na+ ions and Cl- ions. It is completely ionic. AlCl3, being covalent (and not ionic), hydrolyses in water and forms Al(OH)3 and HCl. The resulting solution has a pH of 3.
MgCl2 can be described as ionic but forms a solution with pH of 6.5 when dissolved in water. The slight acidity is attributed to the slight covalent character.
So again, AlCl3 cannot be described as ionic, rather it is a covalent compound. So the right answer is MgCl2[/QUOT

That helped a lot! Thank you.

 

[ashcull14]

NEED HELP :/