Chemistry: Post your doubts here!

[Anallia]

Why doesn't Sodium metal react with Ethanal(aldehyde) to produce hydrogen?

it is because the sodium metal attacks an -OH group. Sodium substitutes the hydrogen on the oxygen forming a salt (O-Na+) giving out hydrogen as the other product....whereas in ethanal there is a C=O bond and a C-H bond, there is no -OH group to attack
hope this helps

 

[x-gamer-x]

it is because the sodium metal attacks an -OH group. Sodium substitutes the hydrogen on the oxygen forming a salt (O-Na+) giving out hydrogen as the other product....whereas in ethanal there is a C=O bond and a C-H bond, there is no -OH group to attack
hope this helps

Do tell me my doubts

Q 14, 16 and 27

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_w11_qp_11.pdf

thanks

 

[kingo44]

How many different substitution products are possible, in principle, when a mixture of bromine
and ethane is allowed to react?
A 3 B 5 C 7 D 9

 

[kingo44]

Under the Montreal Protocol the use of chlorofluorocarbons is to be phased out. Fluorocarbons
are often used to replace them. One chlorofluorocarbon which was widely used as a solvent is
CCl2FCCl F2 and large stocks of it remain. One process to use up these stocks is to convert it into
the fluorocarbon CH2FCF3 by the following route.
CCl
2FCCl F2
step 1
CCl
3CF3
step 2
CH2FCF3 CCl
2FCF3
step 3
What type of reaction is step 1?
A elimination
B free radical substitution
C isomerisation
D nucleophilic substitution

 

[snowbrood]

8 Which compound is the only gas at room temperature and pressure?
A CH3CH2CH2NH2 Mr = 59.0
B CH3CH2CH2OH Mr = 60.0
C CH2OHCH2OH Mr = 62.0
D CH3CH2Cl Mr = 64.5

Answer is D. Why?

well A B and C have hydrogen bonding so they cant be
now we are left with D which has least number of atoms in a molecule is polar but have no hydrogen bonding so it is gaseous simple as that

 

[snowbrood]

35 Solids W, X, Y and Z are compounds of two different Group II metals. Some of their applications
are described below.
Compound W is used as a refractory lining material in kilns.
Compound X is used as a building material. It can also be heated in a kiln to form compound Y. When Y is hydrated, it forms compound Z which is used agriculturally to treat soils.
Which statements about these compounds are correct?
1 More acid is neutralised by 2.0 g of X than by 2.0 g of W.
2 TheMrofXisgreaterthantheMrofYby44.0.
3 The metallic element in Y reacts with cold water more quickly then the metallic element in W.

Answer is 2 and 3, why is 1 wrong?

2/(mr of x or w)
number of moles=2/(mr of x or w)
X is caco3 and w is mgo mgo has less mass so there will be greater number of moles or more acid neutralized by W so 1 is incorrect CaCo3=1oo and Cao=56 100-56=44 2 is correct .ca is down the group so react more violently than mg

 

[x-gamer-x]

snowbrood

Q 14, 16 and 27

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_w11_qp_11.pdf

thanks

 

[snowbrood]

snowbrood

q14 is too easy total mass of limestone(CaCO3) burnt=1200
mr of limestone=100.1
1200/100.1=11.988moles
CaCO3 yields CaO+CO2
11.988*44=527

 

[snowbrood]

snowbrood

snowbrood

we have hydrogen chlorine and sodium hydroxide as products
if u let the products to react
NaOH+cl2== NaCl+NaClO and h20
naoh and cl2 are used up
so B is the answer remember the key words it is cold

 

[snowbrood]

snowbrood

q27
there is a homolytic fission as each radical gets one electron of the shared bond pair
however there is going to be one major product and one minor product so there is 3:1
which one is going to be major one that beyond the scope of our study

 

[x-gamer-x]

snowbrood thank u bro

 

[snowbrood]

snowbrood thank u bro

no problem glad that i could help yea

 

[strangerss]

Finally found an answer ! *sigh of relief*
Quite convincing , thanks !

Oh my GOD I posted this last year , never imagined some one would read it again XD hehe , you're welcome

 

[sikandar7x]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_1.pdf
Please help me with question 12 of this paper. The answer in the marking scheme is B, but I think it is D, since more molecules have higher energies and this increase is greater in D. Why is the answer B?

 

[twisty]

assalamualaikum can some one plsssss clear my doubttttttt plssss
it comes under solubility of product lesson in the equilibrium chapter a2 chem


solubility produst of agcl is 1.46(multiplied)10(to the power of -7) mol(squared)dm(to the power negative 6) at 25(degrees celcius)

0.1 moldm(to the powernegative3) NaCl was added to a saturated soluton of AgCl
calculate the new solubility of AgCl and comment on ure findings

 

[daredevil]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s09_qp_4.pdf

plleasee someone explain question 1 cii

 

[snowbrood]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_4.pdf

plleasee someone explain question 1 cii

 

[snowbrood]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s09_qp_4.pdf

plleasee someone explain question 1 cii

can u please help me sketch that titration curve q1b(iii)

 

[Yash Jain]

friends i have doubt in
9701_w07_qp_1 => Q n0. 13 and 14

 

[Namehere]

friends i have doubt in
9701_w07_qp_1 => Q n0. 13 and 14

For Q13: All of the ions in the question will have an electronic configuration similar to that of Ar. However, the only difference is the nuclear charge. The answer is A - P3- and the reason being it has the least nuclear charge which makes the electrons less attracted compared to the other species. It has also been added 3 extra electrons so the extra repulsion felt by those electrons makes them want to spread out more and so causing a larger radius.

For Q14: A is the only option which makes sense. D cannot be because if the first ionisation energy were to increases down the group the atomic radius would have to decrease down the group, which obviously isn´t true. C cannot be because of similar reason to D. B cannot be because what determines the melting point of a substance (in this case Group II metals) is the charge on the cation and the cloud/sea of delocalised electrons. The greater the charge on the cation, the greater the contribution to the delocalised sea of electrons and so the stronger the metallic bond is, making it have a higher melting point. So B cannot be because all have the same charge on the cation, since they are all in group II. A makes sense because if you look at the periodic table, across the period (atomic number increases by 1) and the mass number increases by more than 1 and so the graph has this kind of curve shape.

Hope it helps.