Chemistry: Post your doubts here!

[Browny]

So that I can contact you if you are not online.

 

[Browny]

Are you getting above 36 for the MCQ's?

 

[Mohammed salik]

So that I can contact you if you are not online.

Check ur Inbox!

 

[AbbbbY]

Will it a trouble if I ask you questions because I have quite a lot(5 to 6 in 1 paper)? Shall I e-mail you shall i ask from here?

Ask here for sure!
It helps other ppl too when browsing through them

 

[Browny]

ok Abby thanks.

 

[MiniSacBall]

Best way to remember the bond angles it is hard for me. And also acid and base hydrolysis of fats. And at room temperature which gas behaves most as ideal gas and high temperature and low temperature.
Any help is appreciated.

 

[Namehere]

Best way to remember the bond angles it is hard for me. And also acid and base hydrolysis of fats. And at room temperature which gas behaves most as ideal gas and high temperature and low temperature.
Any help is appreciated.

Can someone explain Q6f(ii) & (iii)? (My doubt is actually iii, so work on that one first, I just want to make sure if my reasoning behind ii is correct)

Thank you!

 

[Haya Ahmed]

O/N_2009_P12 -- Q10 , Q20

M/J_2012_P12 -- Q28

O/N_2012_P12 -- Q11 , Q15 , Q17 , Q23, Q31 , Q33 , Q38

Please someone help me I'm dying here from confusion !!!

I'm Sorry I know they are too much but please try to help me with what you know because I have a Chemistry P1 Exam the day after tomorrow and I'm so depressed .. I'll be Thankful for the person who will help me ^_^ ..

 

[AbbbbY]

O/N_2009_P12 -- Q10 , Q20

M/J_2012_P12 -- Q28

O/N_2012_P12 -- Q11 , Q15 , Q17 , Q23, Q31 , Q33 , Q38

Please someone help me I'm dying here from confusion !!!

I'm Sorry I know they are too much but please try to help me with what you know because I have a Chemistry P1 Exam the day after tomorrow and I'm so depressed .. I'll be Thankful for the person who will help me ^_^ ..

10: A. They're coming out unchanged at the end of the reaction so yes. They are.

Besides,
B is out. Cl is reduced in B.
C Light initiates the reaction so has to be the first one. Plus depth is relative to the intensity hence defo 1.
D Ag goes from +1 to 0.
Left with A.

20: A

I've answered this soo many times here!

Look. Each double bond or ring formation leads to -2 H.

If it were a totally saturated straight alkane, it'd be C20H42. So, 20 C's can take 42 H atoms
42-28 = 14H missing.
You are told there is one C=O and 1 ring. Additionally, the ring has a double bond. This accounts for 6 missing Hydrogens. So, you're left with 8.
8/2 = 4 double bonds in the aliphatic chain.

4+1 = 5 total.
______

11 A!
Bond energy = energy change when a covalent bond of a GASEOUS MOLECULE is broken to give GASEOUS ATOMS. NOT any other fancy compounds like XY.

15 B

2X(NO3)2 -> 2XO + 4NO2 + O2
4mol NO2 = 184g
1mol O2 = 32g

2mol Be(NO3)2 = 2*133 = 266g giving 216g
2.00 g will give 1.62

2 mol of Ca(NO3)2 = 2*(133+31) =328 giving 216
2.00 will give 1.32 so this is your answer.

Maybe theres a better way, but this is just how I do it.

17

300 cm3 of O2 = 0.3dm3
24 dm3 = 1 mol
0.3 = 0.0125mol

A
2Ca + O2 -> 2CaO
Reacts in 2:1
1.15/40 = 0.0288
0.0288/0.0125 = 2.3

B
Mg, Same group so same ratio.
1.15/24 =0.0479

0.0479/0.0125 = 3.8

C
4K + O2 -> 2K2O
4:1

1.15/39 = 0.029

0.0295/0.0125 = 2.4

D
Na same group so same ratio.
4:1
1.15/23 = 0.05
0.05/0.0125 = 4

So, D. This looks really really long but took me literally 30 seconds on my calculator. Maybe theres another, easier and quicker way that I don't know of.

23 C?
A would give you C2H6 and C2H4 both of which have no isomers.
B would give you C3H8 and C3H6, both of which again have no isomers.
C would give you C4H10 and C4H8 both of which have isomers but non-cyclic.
D isn't possible because well C9!

31 B?

weird question really.
1- N2
2- NH4+
3- ?!!. I'd go with wrong here. Primarily because I've never seen N3+ anywhere in my 2 years. Besides, it forms a cation and gains electrons, generally.
B?

33 I'd probably pick B.

1- Definitely giant
2- Well I guess it is formed used sand, so I'd go with giant.
3- PCl5 is never a giant structure

38 B!

1- Br- is replaced by OH-
2- Remember. Haloalkanes, only time AQUEOUS reagent is used is formation of alcohol.
3- PCl5!

 

[Haya Ahmed]

10: A. They're coming out unchanged at the end of the reaction so yes. They are.

Besides,
B is out. Cl is reduced in B.
C Light initiates the reaction so has to be the first one. Plus depth is relative to the intensity hence defo 1.
D Ag goes from +1 to 0.
Left with A.

20: A

I've answered this soo many times here!

Look. Each double bond or ring formation leads to -2 H.

If it were a totally saturated straight alkane, it'd be C20H42. So, 20 C's can take 42 H atoms
42-28 = 14H missing.
You are told there is one C=O and 1 ring. Additionally, the ring has a double bond. This accounts for 6 missing Hydrogens. So, you're left with 8.
8/2 = 4 double bonds in the aliphatic chain.

4+1 = 5 total.
______

11 A!
Bond energy = energy change when a covalent bond of a GASEOUS MOLECULE is broken to give GASEOUS ATOMS. NOT any other fancy compounds like XY.

15 B

2X(NO3)2 -> 2XO + 4NO2 + O2
4mol NO2 = 184g
1mol O2 = 32g

2mol Be(NO3)2 = 2*133 = 266g giving 216g
2.00 g will give 1.62

2 mol of Ca(NO3)2 = 2*(133+31) =328 giving 216
2.00 will give 1.32 so this is your answer.

Maybe theres a better way, but this is just how I do it.

17

300 cm3 of O2 = 0.3dm3
24 dm3 = 1 mol
0.3 = 0.0125mol

A
2Ca + O2 -> 2CaO
Reacts in 2:1
1.15/40 = 0.0288
0.0288/0.0125 = 2.3

B
Mg, Same group so same ratio.
1.15/24 =0.0479

0.0479/0.0125 = 3.8

C
4K + O2 -> 2K2O
4:1

1.15/39 = 0.029

0.0295/0.0125 = 2.4

D
Na same group so same ratio.
4:1
1.15/23 = 0.05
0.05/0.0125 = 4

So, D. This looks really really long but took me literally 30 seconds on my calculator. Maybe theres another, easier and quicker way that I don't know of.

23 C?
A would give you C2H6 and C2H4 both of which have no isomers.
B would give you C3H8 and C3H6, both of which again have no isomers.
C would give you C4H10 and C4H8 both of which have isomers but non-cyclic.
D isn't possible because well C9!

31 B?

weird question really.
1- N2
2- NH4+
3- ?!!. I'd go with wrong here. Primarily because I've never seen N3+ anywhere in my 2 years. Besides, it forms a cation and gains electrons, generally.
B?

33 I'd probably pick B.

1- Definitely giant
2- Well I guess it is formed used sand, so I'd go with giant.
3- PCl5 is never a giant structure

38 B!

1- Br- is replaced by OH-
2- Remember. Haloalkanes, only time AQUEOUS reagent is used is formation of alcohol.
3- PCl5!

O/N_2009_P12 For Q20 -
I didn't get this part (You are told there is one C=O and 1 ring. Additionally, the ring has a double bond. This accounts for 6 missing Hydrogens. So, you're left with 8. ) Ain't they must be 9 hydrogens (cyclohexene) and 2 hydrogens missing for the double bonds (C=O) so total of 8 ? 14-11 =3

O/N_2012_P12 For Q17 -
What do you mean by same group ratio and all these .. and why did you chose specially 1:4 !?

O/N_2012_P12 For Q23-
((C4H10 and C4H8 both of which have isomers but non-cyclic.)) How is that even possible can you explain further ?

O/N_2012_P12 For Q33 - how am I supposed to know the 2nd one in the exam


Thanks That helped so much you're awesome .. and I think you just forgot Q28 in M/J_2012_P12 ^_^

 

[Mohammed salik]

O/N_2009_P12 For Q20 -
I didn't get this part (You are told there is one C=O and 1 ring. Additionally, the ring has a double bond. This accounts for 6 missing Hydrogens. So, you're left with 8. ) Ain't they must be 9 hydrogens (cyclohexene) and 2 hydrogens missing for the double bonds (C=O) so total of 8 ? 14-11 =3

O/N_2012_P12 For Q17 -
What do you mean by same group ratio and all these .. and why did you chose specially 1:4 !?

O/N_2012_P12 For Q23-
((C4H10 and C4H8 both of which have isomers but non-cyclic.)) How is that even possible can you explain further ?

O/N_2012_P12 For Q33 - how am I supposed to know the 2nd one in the exam


Thanks That helped so much you're awesome .. and I think you just forgot Q28 in M/J_2012_P12 ^_^

q33 :- Baked clay is also known as Ceramic, however, true is that ceramics all have giant structures of one type or another, with strong bonds between the atoms (or ions) which make them up.

 

[ZaqZainab]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
q28

 

[Mohammed salik]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
q28

Q28) (C) Because Ester is hydrolyzed it breaks down inot acid + alchol
In this case CH3CH2CH2CO2CH3 gives CH3CH2CH2COOH +CH3OH
It asks for empirical formula of acid.
so C4H8O2 .. divide this by 2 to get simplest ratio(empirical formula)
C2H4O..
Hope I Helped

 

[Namehere]

Abby, did you have time to find any physics "factsheets" ?

 

[ZaqZainab]

Q28) (C) Because Ester is hydrolyzed it breaks down inot acid + alchol
In this case CH3CH2CH2CO2CH3 gives CH3CH2CH2COOH +CH3OH
It asks for empirical formula of acid.
so C4H8O2 .. divide this by 2 to get simplest ratio(empirical formula)
C2H4O..
Hope I Helped

oh i didn't divide by 2 dumb me

 

[Mohammed salik]

oh i didn't divide by 2 dumb me

Its Ok

 

[ZaqZainab]

Its Ok

Thanks
can you help me with 36 and 40

 

[Mohammed salik]

Thanks
can you help me with 36 and 40

Q40:-D first form an equation:-
CH3COOH + Ca gives (CH3COO)2Ca.. because Ca is 2+ and Acid is 1-!!
2(CH3COO) IS EQUAL TO C4H6O4!! so One is correct!! Others are dionic meaning having two COOH groups so they would never form C4H6O4Ca!!

 

[ZaqZainab]

Q40:-D first form an equation:-
CH3COOH + Ca gives (CH3COO)2Ca.. because Ca is 2+ and Acid is 1-!!
2(CH3COO) IS EQUAL TO C4H6O4!! so One is correct!! Others are dionic meaning having two COOH groups so they would never form C4H6O4Ca!!

Thanks again and what about 36th?

 

[Mohammed salik]

Thanks
can you help me with 36 and 40

36:-A
Option 1: NO + 1/2 O2 gives NO2 so the oxidation number does increase by Two!!
Option3:-Yes it is polar... If you compare the electronegativities Oxygen is around 3.5 and N is 3.0 approx.
If 1 and 3 are correct no need to look at 2 Direct ans is A!!
Sorry For being Lateee