Chemistry: Post your doubts here!

[darknessinme]

31 Which statements are correct in terms of the Brønsted-Lowry theory of acids and bases?
1 Water can act as either an acid or a base.
2 Sulfuric acid, H2SO4, does not behave as an acid when dissolved in ethanol, C2H5OH.
3 The ammonium ion acts as a base when dissolved in liquid ammonia.

Answer is 1 only, why?

Acids are proton donors, and bases are acceptors of protons. If bases are proton acceptors, then the base must have a lone pair to accept the H+.
1. You should know water is amphoteric.
2. Sulfuric acid can act as an acid because the oxygen atom in ethanol has two lone pairs, either of which can accept the proton.
3. Ammonium ions don't have a lone pair, so can't accept protons ie. acts only as an acid. Ammonia does have a lone pair so it would be the base while NH4+ would be the acid.

So only 1 is true.

 

[Jessie N.]

these quations are given in data booklet so no need to memorize it
Sn2+⇌ Sn4++ 2e- equation 1
(MnO4–)+ (8H+)+ 5e– ⇌ (Mn2+)+ 4H2O) equation 2
balance the number of electrons so that each equation have same number of electrons
multiply equation 1 by 5 and equation 2 by 5
and then add these equations we get
(16H+)+(5Sn2+)+2MnO4- yields (5sn4+)+2Mn2+
ignore the liquid we are concerned with ions and ions only
2moles of mno4- reacts with 5moles of sn2+
2/5moles of mn 1 moles sn
(9.5/190)*2/5 9.5/190

thanks a lot！！！！！

 

[Christy26]

The table describes some of the chemistry and thermodynamic properties of the halogens.

Process ............... ..Name and Symbol of quantity​

2HX(g) → H2(g) + X2(g)...... enthalpy change of reaction, Hr
H2(g) + X2(g) *-->< 2HX(g).... equilibrium constant, Kp
X(g) → X+(g) + e–.................... ionisation energy, Hi

P.S * -->< means equilibrium reaction

Which statements about the relative values of these quantities are correct?
1 Hr for HCl > for HBr
2 Kp for HBr > Kp for HI
3 Hi for I > Cl

The answers are 1 and 2. But why ?
Can someone explain this ?
Thanks in advance.

 

[Jinosupreme]

Which mixtures, on heating, produce the gas ND3? [D = an isotope of hydrogen]
1 CaO(s) and ND4Cl(s)
2 CH3CN and NaOD in D2O
3 NDH3Cl and NaOD in D2O

Need help with this question
Answer is 1 and 2 only. Why no 3?

 

[Jinosupreme]

The table describes some of the chemistry and thermodynamic properties of the halogens.

Process ............... ..Name and Symbol of quantity​

2HX(g) → H2(g) + X2(g)...... enthalpy change of reaction, Hr
H2(g) + X2(g) *-->< 2HX(g).... equilibrium constant, Kp
X(g) → X+(g) + e–.................... ionisation energy, Hi

P.S * -->< means equilibrium reaction

Which statements about the relative values of these quantities are correct?
1 Hr for HCl > for HBr
2 Kp for HBr > Kp for HI
3 Hi for I > Cl

The answers are 1 and 2. But why ?
Can someone explain this ?
Thanks in advance.

1) Bond energy of HCl is higher than HBr, hence will has a high enthalpy change for HCl compare to HBr.
2) HBr bond energy higher tha HI, as if HBr formed, harder to form back to H2 and Br2, but it is easier for HI to form back H2 and I2, hence the Kp for HBr is higher than HI.
3) it is wrong as I is below Cl in Group 7, should have lower first ionisation energy

Hope this helps

 

[Christy26]

1) Bond energy of HCl is higher than HBr, hence will has a high enthalpy change for HCl compare to HBr.
2) HBr bond energy higher tha HI, as if HBr formed, harder to form back to H2 and Br2, but it is easier for HI to form back H2 and I2, hence the Kp for HBr is higher than HI.
3) it is wrong as I is below Cl in Group 7, should have lower first ionisation energy

Hope this helps

Thanks !

 

[periyasamy]

I chose A, why cant? Answer is B




Answer is D, I understand why it is structural isomer, but donno why osmotic pressure increase.

Answer is A.

Why??

Buddy,for 1st question i think the option a is not taken because ammonia is solluble in h20 soits conductivity in aqeous should be solluble.
For the 2nd question generally osmotic pressure increase when solute added to solvent.The addition of solute(h20) cause molarity to increase n the osmotic pressure increase as well
For the 3rd question in order if u want to find an answer in Hess law,it is vital to know two types of enthalpy change,as then only relation can be made.In this case option b and d is cancelled.Answer cant be option c because u need an extra value that is heat change of combustion of ch4,then only can do.
Hope it helps.....

 

[periyasamy]

Which pairs of homologous series have the same C:H ratio in their general formulae?
1 aldehydes and ketones
2 carboxylic acids and esters
3 alkenes and ketones

Answer is 1,2,3

Help :O

Buddy,easier way to do this is draw a basic structure for all options given that their carbon no is same.

 

[SIstudy]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w03_qp_1.pdf
Q2?? I don't get how to solve it :/ can sum1 pls explain it?

 

[SIstudy]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w04_qp_1.pdf
Q1?
how to solve it? I take alot of time when doin this :/

 

[Jessie N.]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w03_qp_1.pdf
Q2?? I don't get how to solve it :/ can sum1 pls explain it?

hope you can understand

 

[Jessie N.]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w04_qp_1.pdf
Q1?
how to solve it? I take alot of time when doin this :/

sorry for my handwriting lol

 

[Jessie N.]

Can someone explain these three questions to me pleaseeee :/

 

[periyasamy]

Hai,need help here.Ans is D.

 

[U7X0GXO]

Hai,need help here.Ans is D.

you haven't provided the options :/

 

[periyasamy]

you haven't provided the options :/

oops ,sorry boss.
A=1,2 AND 3
B=1 AND 2
C=2 AND 3
D =ONLY 1

 

[snowbrood]

oops ,sorry boss.
A=1,2 AND 3
B=1 AND 2
C=2 AND 3
D =ONLY 1

i thnk the answer is D
W should be magnesium oxide which is used as a refractory lining the furnace.
and X can be Calcium carbonate which when heated decomposes to Calcium oxide which then hydrated gives calcium hydroxide. calcium hydroxide is an alkali and cant decrease the ph of soil (all group 2 elements are alkalis so they cant decrease the ph)
u do know that calcium is more reactive than magnesium so option 2 and 3 are incorrect
W magnesium oxide has less mass as compared to calcium carbonate
so 1/23+oxide gives more number of moles than 1/40+carbonate
as number of moles=1/A if u increase A u decrease the number of moles and likewise

 

[periyasamy]

i thnk the answer is D
W should be magnesium oxide which is used as a refractory lining the furnace.
and X can be Calcium carbonate which when heated decomposes to Calcium oxide which then hydrated gives calcium hydroxide. calcium hydroxide is an alkali and cant decrease the ph of soil (all group 2 elements are alkalis so they cant decrease the ph)
u do know that calcium is more reactive than magnesium so option 2 and 3 are incorrect
W magnesium oxide has less mass as compared to calcium carbonate
so 1/23+oxide gives more number of moles than 1/40+carbonate
as number of moles=1/A if u increase A u decrease the number of moles and likewise

Thank u,boss.
Thanks for always helping.Hope u get awesome results ,surely u deserve it.

 

[periyasamy]

Can someone explain these three questions to me pleaseeee :/

For question 25,ans is d.This is because when dehydration occur there is 2 possibilty for the double bond to occur.I think u know this but why option d is selected is try to imagine the structure is rotated 180 degree n it will make sense.It is the same structure but just inverted the other way around.(I think that is the reason)
For question 31------ans should be a.if u do one by one for 1st option both have 3 unpaired p electron ,for option 2 both have three unpaired p electron and for option 3 both have 2 unpaired p electron.Just write them down n then check it.
For last question---i am not sure but i have seen someone answering that only the 1st option,ethanedioc acid is rite to cancel out the charge of 2+ of calcium ion....
Hope it helps.....

 

[periyasamy]

I need help for this question .I tried many times but cant get an answer for this.Thanks.Ans is c.