Chemistry: Post your doubts here!

[Jinosupreme]

Hi, anybody can help me?
Nov 2011-13 Q28

A reaction between chlorine and propane in ultraviolet light produces two isomeric
monochloropropanes, C3HCl, as products. Which information about this reaction is correct?

expected ratio of 1-chloropropane to 2-chloropropane produced
A 3:1
B: 1:1

Answer is 3:1
As propane CH3-CH2-CH3 there's total 6 H atom at the side C, but only 2 H atom at the C-2. Hence the chance of getting replace the H with C-1 will be 6 which form 1 chloropropane , and centre will be 2 which form 2 chloropropane,
6:2
Hence is 3:1 hope this helps

 

[Trevor Jts]

Answer is 3:1
As propane CH3-CH2-CH3 there's total 6 H atom at the side C, but only 2 H atom at the C-2. Hence the chance of getting replace the H with C-1 will be 6 which form 1 chloropropane , and centre will be 2 which form 2 chloropropane,
6:2
Hence is 3:1 hope this helps

Great! TQ!

 

[Jinosupreme]

Hai guys,why is y in this question has an observation of colourless solution?Thanks

The reaction is HCl + KI -> KCl + HI. No I2 form, hence is colourless as HI is a colourless solution

 

[periyasamy]

The reaction is HCl + KI -> KCl + HI. No I2 form, hence is colourless as HI is a colourless solution

Bro,I think u made a small mistake there.Your explanation is for x .Nevertheless,I think i know what happened in yIts practically Agcl react with aqeous nh3 .The ppt gets dissolved n form colourless solution.Thank u boss.

 

[*MK*skydiver :D]

Hi M
Hi Mk driver, I'm not good in explaining but I can at least do Q12 in Nov 2005 for you.
Equation being formed is:
2Mg + O2 --> 2MgO
4Al +3O2 ---> 2Al2O3
S + O2 ---> SO2
Simplifying them since you need one mole of reactant, you'll get:
Mg + 0.5O2 ---> MgO
Al + 0.75O2 ---> 0.5Al2O3
S + 1O2 ---> SO2
Hence the trend in option D

For your Nov 2011-12 question,
Ba(NO3)2 ----> BaO + 2NO2 + 0.5O2
and Mg will b oxidised also to MgO because it says barium nitrate is oxidising agent.
I also dono this question at first, but my teacher solved it just in a matter of seconds haha. Good luck if youre taking A LEvels tomoro!

Thank you
I am taking the exam tomorrow in shaa Allaah , good luck for you too!

 

[x-gamer-x]

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

 

[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?