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P1 MCQ's preparation thread for chemistry ONLY!!!!

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Do you know how to do Qs (27),(26) and the (30)?
(26)Difficult to choose between C and D.
(27)Difficult to choose between A and C.
(30)Difficult to choose between C and D.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s04_qp_1.pdf
27. How can you get CH2BrCH2OH from CH2CH2? Electrophilic addition will yield CH2BrCH2Br. To get the CH2BrCH2OH, you'll need an additional step - nucleophilic substitution. A is wrong; both products are not obtained by electrophilic addition.
30. HCN won't reaction with the C=C double bond in the compound C, it'll only react with the CHO group. So only 1 mole of HCN will react with the compound in C.
 
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12. The top of the curve becomes lower, so it can be either B or D. D's area is much less than the area of the first graph, so it's B.
18. In A & B, a co-ordinate covalent bond is set up between the lone pair and I and H. In D too a co-ordinate covalent bond is set up between the lone pair of one NH3 and that of another.
37. An ethane and chlorine molecule in sunlight will produce many free radicals. C2H5 will react with another C2H5 to give molecule B. A will be formed as the main product. C will be formed when a C2H4Cl free radical reacts with another C2H4Cl molecucle.
38. The C-Br and C-I bonds are weaker than the C-Cl bond, so they will be broken faster and AgI and AgBr will be formed faster than AgCl. AgCl will be formed faster for compound 1 also because there are 2 C-Cl bonds.
 
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Q21. B) Citric acid (from top to bottom): The first carbon is bonded to 2 hydrogens, so it's not chiral. The second carbon is bonded to the top and bottom chains which are the same, so it's not chiral. The third carbon is bonded to 2 hydrogens, so it's not chiral.
Isocitric acid (from top to bottom): The first C is bonded to 2 hydrogens, so it's not chiral. The second carbon is bonded to the top chain, an H, a CO2H, and the bottom chain, so it is chiral. The third carbon is bonded to the upper part of the molecule, an OH, an H, and a CO2H, so it is chiral.
Conclusion: Citric acid has 0 chiral centres and isocitric acid has 2 chiral centres

Q22. D) P is an alkene and a primary alcohol. Alkenes are oxidized by hot concentrated KMnO4 to carboxylic acids with two carboxylic acid groups. Primary alcohols are oxidized to a carboxylic acid. This means that the products of this oxidation are CH3CH2CO2H (from primary alcohol oxidation) and HO2CCH2CO2H (from alkene oxidation)

Q23. B) Write down some equations for the complete combustion of simple alkanes so as to determine how the ratio of carbon atoms to moles of oxygen changes as there are more carbon atoms in the alkane.
CH4 + 2O2 → CO2 + 2H2O
2C2H6 + 7O2 → 4CO2 + 6H2O
C3H8 + 5O2 → 3CO2 + 4H2O
The ratio of carbon atoms to moles of oxygen in each equation respectively is:
1:2, 2:7, 3:5
The number of carbon atoms is directly proportional to the number of moles of oxygen, so the answer has to be B

Q24. B) When an alkene reacts with cold liquid bromine, dibromoalkene is formed. Since the compound above is made up of two alkenes, then four bromine atoms are added on to the molecule. This reaction is an electrophilic addition reaction. Each bromine atom adds on to a carbon engaged in the double bond. The answer is 1,3,4,6 - tetrabromocyclohexane


Q25. D) Reaction D is a nucleophilic addition (CN- is the nucleophile)

Q26. A) When a halogenoalkanes reacts with KCN in ethanol, a nucleophilic substitution reaction takes place, in which the CN- ions substitute the halogen atoms (in this case the bromine atoms from 1,4-dibromobutane)


Q27. C) The weakest bond is the C-Cl bond. The C-H bond is very strong because it is an ionic bond. The C-F bond is strong because fluorine is very electronegative. The C-Cl bond however, is covalent and Cl is not as electronegative as Fluorine, which means that it is a relatively weak bond (relative to the other bonds in the molecule). This is why in the reaction, the most susceptible atom to leave the molecule is chlorine, and so the radical in option "C" is formed

Q28. D) When an alcohol reacts with sodium an alkoxide ion is formed (O-Na+). When a carboxylic acid reacts with sodium, since it's an acid, a salt is formed (COONa). The only compound that forms one mole of hydrogen is the last one.
CH3CH(OH)CO2H + 2Na → CH2CH(ONa)COONa + H2

Q29. C) An alcohol and concentrated sulphuric acid under reflux will produce an alkene which can be purified by dilute sodium hydroxide (base hydrolysis of esters).

Q30. D) When propanone reacts with hydrogen cyanide, nucleophilic addition takes place and a hydroxynitrile is formed.
CH3COCH3 + HCN → CH3C(OH)CH3CN
2-hydroxybutanenitrile is hydrolysed under acidic conditions to Butanoleic acid
CH3C(OH)CH3CN + H2O + H+ → (CH3)2C(OH)CO2H + NH4

Q31. C) Silicon tetrachloride doesn't have co-ordinate bonding because it follows the octet rule, sharing all of its valence electrons with the chlorine atoms.
Both silicon and chlorine are non-metals, so, it has covalent bonding.
There are instantaneous dipole-induced dipole forces between the molecules (Van der Waals forces)

Q32. A) The right-hand side of the structure is polar and since water is a dipole, it is attracted to water.
The alkyl chain is non-polar and attracted to other alkyl chains by Van der Waals forces. Since oil is of a similar character to this alkyl chain, the alkyl chain is soluble in oil droplets.
In alkanes, each carbon atom forms a tetrahedral structure (due to sp3 hybridisation), so the C-C-C bond angles are tetrahedral

Q33. A) The reaction is endothermic, which means that diamond has more energy than graphite. The enthalpy change of atomisation is the enthalpy change when one mole of gaseous atoms is formed from one mole of the element in the standard state. Since diamond has more energy than graphite, it requires a smaller enthalpy change of atomisation.
Since the enthalpy change of atomisation is smaller in diamonds, it means that the C-C bonds in diamond are weaker than in graphite because it requires less energy to change into the gaseous state.
Since diamond has more energy than graphite, there is a higher energy requirement to break the C-C bond to form new C=O bonds (in carbon dioxide) in combustion.


Q34. C) The electronegativity difference decreases between the elements (3.05, 2.13, 1.43, 0.65)
All of the compounds fulfill the octet rule and are isolelectronic.
The compounds become increasingly covalent (starting from ionic)

Q35. B) Sulphur dioxide is a reducing agent which prevents oxidation.
Since it's an anti-oxidant, it prevents alcohols from oxidizing to carboxylic acids (prevents sour-tasting acids).
It does smell and is toxic in large quantities.

Q36. C) Iodide ions are strong reducing agents and so they reduce the sulphuric acid, first to sulphur dioxide, then to sulphur and then hydrogen sulphide. Barely any hydrogen iodide is formed because it's displaced by the sulphuric acid.
Iodide ions are reducing agents, and become oxidised to iodine.
The majority of the products of the reaction are sulphur compounds (as explained above)

Q37. B) A chiral centre is an atom bonded to four different groups.
An optical isomer (geometric isomer) occurs when there's a chiral centre.
Chiral carbon atoms DO NOT need to have structural isomers.


Q38. B) Step X is a nucleophilic substitution because the reagent is hot aqueous sodium hydroxide (OH- being the nucleophile).
A chloroalkane cannot be formed by reacting sodium chloride with alcohol. It can be done with phosphorus (III) chloride or phosphorus (V) chloride.

Q39. C) Only an aldehyde forms a brick-red precipitate with Fehling's solution. Aldehydes are formed by the oxidation (in acidified dichromate) of primary alcohols. The two primary alcohols are CH3CH2CH2OH and CH3OH

Q40. B) It only has one chiral carbon (The one in the middle).
It has a carboxylic acid group, so it can be esterified by ethanol. It has an OH group, so it can be esterified by ethanoic acid.
The molecule contains tertiary and primary alcohols, not secondary.

P.S :- Others please post work solutions for all P1 yearly like this.. :)
i know its 2 much to ask but can you plz post the same for nov 2003
 
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no ... my sir specified that if there is no receiver at the end it is reflux
But CIE meant the apparatus in Q.40 to be a reflux apparatus. You can tell it wasn't meant to be a distillation apparatus because none of the reactions 1/2/3 show a distillation reaction.
 
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1. You have to construct a balanced equation for the reaction given.
2. 100 g of fertiliser contains 15 g of N, so 14 g will be in x grams of fertiliser. c=n/v=x/5.
6. m=density x volume =1 gram. n=m/Mr=1/18=0.055555. Now use pV=nRT, taking care of the units.
15. Write a balanced equation for the decomposition of CaCO3 and then use mole ratios.
26. It turns into a carboxylic acid because the Oxygen atoms are doubled. That means it must first be oxidised to an aldehyde, therefore it must be a primary alcohol.
31. Write the equations for the complete combustion of all the compounds and see which ones have a mole ratio 1:2.5.

1. Construct a balanced equation and use the mole ratio.
2. Act like the volume = the moles. 1 mole of CS2 will react with 3 of O2, so if 5 O2 moles are provided, 5-3=2 will be left over. 1 mole of CO2 and 2 of SO2 will be made. The moles left=2 (SO2) plus 1 (CO2) plus 2 (O2 left over). That'll make it 5 moles. That's 50 cm3. NaOH is alkaline and CO2 & SO2 are acidic. 1 mole of CO2 and 2 moles of SO2 are used up. 5-3=2 moles.
4. Just count the electrons!
30. 30+30=60-18(water)=42. 22/42 x 100 = 52%.
 
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Can you explain no4 q38.

AgX is formed when there are X- ions. X- ions are released when the C-X bond is broken. C-Br and C-I are weaker than C-Cl so they will be broken more easily and AgBr and AgI will be formed faster than AgCl. Option 1 is included because there are two C-Cl bonds so there will be more Cl- ions released, even though the speed of release will remain the same.
 
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12. The top of the curve becomes lower, so it can be either B or D. D's area is much less than the area of the first graph, so it's B.
18. In A & B, a co-ordinate covalent bond is set up between the lone pair and I and H. In D too a co-ordinate covalent bond is set up between the lone pair of one NH3 and that of another.
37. An ethane and chlorine molecule in sunlight will produce many free radicals. C2H5 will react with another C2H5 to give molecule B. A will be formed as the main product. C will be formed when a C2H4Cl free radical reacts with another C2H4Cl molecucle.
38. The C-Br and C-I bonds are weaker than the C-Cl bond, so they will be broken faster and AgI and AgBr will be formed faster than AgCl. AgCl will be formed faster for compound 1 also because there are 2 C-Cl bonds.

thanks ;)
that was really helpful .. what about my MAIN doubt . i guess u didnt see it :p no. 10 ?
in q no. 39 ..y cant the oh be dehydrated?
 
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Explanations for (7) and (26) Qs May/June 2008 paper,
(7) Al has metallic bond ,P has covalent bonds , so A isn't the answer.
Cl has covalent bonds, an Ar is unreactive(noble gas) , so no bond present between atoms in Ar, so B isn't an answer.
Mg has metallic bond ,Si has covalent bonds , so C isn't the answer.
Both S and Cl have covalent bonds, so D is the correct answer.

(26) since alcohol reacts with MnO4-/H+ , alcohol is either primary or secondary ,and NOT tertiary as tertiary alcohols aren't oxidised.
since a carboxyllic acid is formed alcohol is a primary alcohol and NOT a secondary alcohol , since secondary alcohols are oxidised to ketones.
For primary alcohol to form 2 H atoms attached to C , and this is possible in C only.
 
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AgX is formed when there are X- ions. X- ions are released when the C-X bond is broken. C-Br and C-I are weaker than C-Cl so they will be broken more easily and AgBr and AgI will be formed faster than AgCl. Option 1 is included because there are two C-Cl bonds so there will be more Cl- ions released, even though the speed of release will remain the same.

hEy im having serious problms in Chem oct/nov 2010 varient 12 ........Q:39,38,33,29,27,26,25,13,11,8,4 .....kindly hlp
 
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