CHEM MCQ HELP

[omerkc1]

http://www.xtremepapers.me/CIE/Internat ... _qp_11.pdf


I dont get question number 1..........

 

[alphabravocharlie]

Aoa. i think it is C. That is because since they said has 3 electrons in outer most shell, so it must be a half filled p orbital. half filled p orbitals are found in group 5 of the periodic table. 15 was the only one from group 5, so C.

 

[Abdulrab]

ery n00b at chemistry hope i can get more knowledge here..hahaha
its nov 03..
and please include some explanations on the answers given

15 One mole of each of the following compounds is strongly heated and any gas produced is
collected at room temperature and pressure.
From which compound is 24dm3 of gas likely to be collected?
[One mole of any gas occupies 24dm3 at room temperature and pressure.]
A MgCl2 B MgCO3 C Mg(NO3)2 D Mg(OH)2

16 In black and white photographic film, light converts silver chloride into metallic silver. After the film
has been developed, the unexposed silver chloride is removed by reaction with sodium
thiosulphate to produce a ‘fixed’ negative.
AgCl + 2Na2S2O3 → 4Na+ + Cl – + [Ag(S2O3)2]3–
What is the function of thiosulphate?
A to make the silver ions soluble
B to oxidise the silver ions
C to oxidise the silver metal
D to reduce silver ions

26 Which alcohol gives only one oxidation product when warmed with dilute acidified potassium
dichromate(VI)?
A butan-1-ol
B butan-2-ol
C 2-methylpropan-1-ol
D 2-methylpropan-2-ol

27 What will react differently with the two isomeric pentanols, (CH3)3CCH2OH and
(CH3)2CHCH2CH2OH?
A acidified aqueous potassium manganate(VII)
B concentrated sulphuric acid
C phosphorus pentachloride
D sodium

28 How many hydrogen atoms in a molecule of glycerol, HOCH2CH(OH)CH2OH, may be substituted
by deuterium on dissolving it in an excess of D2O?
A 2 B 3 C 5 D 8

35 A farmer spreads lime on land which has already been treated with a nitrogenous fertiliser.
Which reactions will occur over a period of time?
1 Ca(OH)2 + CO2 → CaCO3 + H2O
2 Ca(OH)2 + 2H+(aq) → Ca2+(aq) + 2H2O
3 Ca(OH)2 + 2NH+
4(aq) → Ca2+(aq) + 2NH3 + 2H2O

and the last question is no 40, cant post it here because it contain picture.

ohh,and can anyone tell me about the concept of optical isomer? I understand that it is a carbon atom bonded to 4 different groups, but when we are given a ring or a long chain, i dunno how to choose the chiral carbon, can anyone give tips on this??

thanks very much..

 

[alphabravocharlie]

Aoa. Dude sorry the mcq's are difficult, but can explain the optical isomers part. In a chain, first check whether the chain contains a double bond. ignore any c atom which has a double bond. Then simply check all the remaining C atoms and see which is bonded to 4 different atoms i.e in HO2CCH2[CH2]3CHCO2H , in this the bold C atom is a chiral as it is the only C atom which is bonded to 4 diff atoms.

 

[CommonSense]

the answer for 15 is B because only 1 mole of carbon dixide is produced whereas A does not decompose, C produces nitrogen dioxide and oxygen and D produces water which is not a gas at room temperature and pressure.
the answer for 16 is A because there was no change in the oxidation number of silver.
the answer for 26 is B because it is a secondary alcohol which will produce only ketone whereas A and C are primary and will form aldehyde and carboxylic acid, and D is tertiary and will not be oxidised.
the answer for 27 is B because both alcohols are primary so with A they will form aldehyde, with C they will form a chloroalkane and with D they will form sodium alkoxide, with B the first one will form an alkene but with the second one something wierd is happening.
the answer for 28 is B because the compound has three -OH groups so the hydrogens can be easily dispalaced due to the high electronegativity of oxygen.
the answer for 35 is A because 2 (and 1) is an acid base reaction, 3 is a acid ammonium salt reaction and 1 u just have to know it.
the answer for 40 is D because the compund is an ester and they products are DISTILLED, only 1 will be in the distillate because it has lower boiling point than 2. as for 3 it cant form because it is obviously wrong because it is supposed to be a sodium carboxylate not an alcohol.
i hope i was helpful.
please if u are not convinced or in doubt with my answers u can post ur reply and i will be viewing this topic regularly.

 

[Saturation]

http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_s10_qp_11.pdf


I dont get question number 1..........

Yeah, it's C, as said earlier, the only one that fits the criteria is 15 (P) , which has 1 electron in each of it's 3p orbitals.

 

[Mobeen]

the answer for 15 is B because only 1 mole of carbon dixide is produced whereas A does not decompose, C produces nitrogen dioxide and oxygen and D produces water which is not a gas at room temperature and pressure.
the answer for 16 is A because there was no change in the oxidation number of silver.
the answer for 26 is B because it is a secondary alcohol which will produce only ketone whereas A and C are primary and will form aldehyde and carboxylic acid, and D is tertiary and will not be oxidised.
the answer for 27 is B because both alcohols are primary so with A they will form aldehyde, with C they will form a chloroalkane and with D they will form sodium alkoxide, with B the first one will form an alkene but with the second one something wierd is happening.
the answer for 28 is B because the compound has three -OH groups so the hydrogens can be easily dispalaced due to the high electronegativity of oxygen.
the answer for 35 is A because 2 (and 1) is an acid base reaction, 3 is a acid ammonium salt reaction and 1 u just have to know it.
the answer for 40 is D because the compund is an ester and they products are DISTILLED, only 1 will be in the distillate because it has lower boiling point than 2. as for 3 it cant form because it is obviously wrong because it is supposed to be a sodium carboxylate not an alcohol.
i hope i was helpful.
please if u are not convinced or in doubt with my answers u can post ur reply and i will be viewing this topic regularly.

yes these are correct .