Chemistry: Post your doubts here!

[sanisha 1234]

will anyone tell me about the tips of paper 5 n dependent ,independent variable

 

[MemoryMatrix 21]

will anyone tell me about the tips of paper 5 n dependent ,independent variable

Ya............independent variable is da one u r changing n dependent variable is a 1 that is supposed 2 b kept constant!
Independent variable is plotted on x-axis n dependent variable on y-axis!

 

[1357911]

Aoa.
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_41.pdf
Q-4 c??

 

[Dr.MMM]

Two equilibria are shown below.

reaction I 2X2(g) + Y2(g) gives 2X2Y(g)
reaction II X2Y(g) gives X2(g) + 1/2Y2(g)

The numerical value of Kc for reaction I is 2.

Under the same conditions, what is the numerical value of Kc for reaction II?
answer is 1/under root 2

EXPLAIN HOW

 

[salvatore]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_42.pdf
Could someone please explain qn no. 3(c) - the whole of it. I don't know how to solve it
Pleaseee!!

 

[Jinosupreme]

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?

 

[Jinosupreme]

Which reaction will give 2-chloropropane in the best yield?
A propane gas with chlorine gas in the presence of ultraviolet light
B propan-2-ol with dilute NaCl (aq)
C propan-2-ol with SOCl 2
D propene with dilute HCl (aq)

I chose D, why cannot? Answer is C.

 

[Jinosupreme]

The products obtained by cracking an alkane, X, are methane, ethene and propene.

The mole fraction of ethene in the products is 0.5.

What is the identity of X?
A C6H14
B C8H18
C C9H20
D C11H24

Answer is B. I don't really understand the question, what does it mean the mole fraction of ether is 0.5? Pls help thanks!

 

[Jinosupreme]

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??

 

[Jinosupreme]

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

 

[Musab100]

any can help me plz ?????

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_11.pdf

MCQs :

11
15
17
23
30
33

 

[Jessie N.]

A solution of Sn2+ ions will reduce an acidified solution of MnO4– ions to Mn2+ ions. The Sn2+ ions are oxidised to Sn4+ ions in this reaction.
How many moles of Mn2+ ions are formed when a solution containing 9.5 g of SnCl 2 (Mr: 190) is added to an excess of acidified KMnO4 solution?

help plzzzzzz

 

[snowbrood]

A solution of Sn2+ ions will reduce an acidified solution of MnO4– ions to Mn2+ ions. The Sn2+ ions are oxidised to Sn4+ ions in this reaction.
How many moles of Mn2+ ions are formed when a solution containing 9.5 g of SnCl 2 (Mr: 190) is added to an excess of acidified KMnO4 solution?

help plzzzzzz

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

 

[snowbrood]

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?

actually u might know water is amphoteric oxide and sulfuric acid is an acid this settles it i think u might be confused with 3
ammonia is base as it accepts protons however ammonium ion nh4+ cant accept any protons rather it will donate protons behaving as an acid.
u can also sum it up like what was once acid after dissociating it will be base. and likewise

 

[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 !