Qualification > Sciences
chem. questions
sweetie:
--- Quote from: tmisterr on May 01, 2010, 05:54:16 pm ---m/j 07
q5 c, cyanide has a triple bond so 3 bonding pairs. Nitrogen shares 3 electrons leaving 2 forming one lone pair. Carbon has a charge of -1 in cyanide so it has an extra electron. it shares 3 electrons and leaves two again forming one lone pair
q26 c, it cannot react with acidified manganate(VII) ions so it has to be a tertiary alcohol. the simplest tertiary alcohol is butanol but its is not chiral, next is pentanol again not chiral and has no chiral isomers neither does hexanol, but a 7 carbon alcohol (2-methylhexan-2-ol) is chiral since the central carbon is bonded to four different groups, CH3, C2H5, and C3H7 ( try drawing it to visualize it better)
q28 c, it decolourises 2,4-DNPH so it must be a ketone or an aldehyde but it also de-colourises manganate(VII) ions so it must be able to be oxidised. ketones cannot be oxidised further, but aldehydes can so C
q40 D, 1 only, heating an easter with an acid will hydrolysithe ester bond and therefore break it. alcohol or sodium hydrogen-carbonate will have no effect the ester bond.
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but how do we know its not chiral???
like in butanol one of the carbon atoms cud have H2, OH, CH3CH2, and a CH2 grps around it... so they r diff.
so why is butanol not chiral??????
sweetie:
--- Quote from: tmisterr on May 01, 2010, 06:53:55 pm ---O/N 07
q10 use mole ratios, 0.8 mole of oxygen was made from (0.8*2)=1.6 mole of nitrogen dioxide so at equilibrium, there is 4-1.6=2.4 mole of nitrogen dioxide. since 1.6 mole of oxygen reacts, then there is 1.6 mole of NO. as you know co-efficient of the compounds in the equations is the power of the concentrations in the Kc equation so answer is D
q19 is B. I will have a chiral centre if the Br and I atom are on the same carbon, so this eliminates C. now check III and IV since II is common is all so no need to check it. III is chiral when it is 1,2-di-iodopropane. IV cannot be chiral, the double bond eliminates two carbons and there is no way it can be arranged to make the third chiral.
q21 reaction between methane and chlorine is a free radical substitution and is not an equilibrium, this automatically rules out B and C, the rate of reaction increases if concentration if reagents increase (methyl free radicals) so A.
q30 is B, when the ester breaks it will form butanoic acid which has the molecular formular C4H8O2 which in its simplest form is C2H4O (Divide all by 2)
q35 is B, when a metal nitrite is heated you get the oxide and NO2 and O2 so BaO will be formed. Mg is oxidised so MgO is formed, no way in which Magnesium nitrite can form.
q33 is C, really gotta go but will explain real soon
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Thank You sooo much
+rep
but in Q21, why is D wrong????
and in que. 19 comp.II also has a double bond , so is it chiral or no????
tmisterr:
--- Quote from: sweetie on May 02, 2010, 01:06:14 pm ---but how do we know its not chiral???
like in butanol one of the carbon atoms cud have H2, OH, CH3CH2, and a CH2 grps around it... so they r diff.
so why is butanol not chiral??????
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how can H2 happen? its not possible, each hydrogen has to be bonded to a carbon or an oxygen, you cannot have two hydrogen atoms bonded to each other. again the CH2 will only have three bonds from it, it needs to have 4 bonds so this cannot happen. Butanol is not chiral, the primary, secondary or tertiary forms of it are all not chiral.
tmisterr:
--- Quote from: sweetie on May 02, 2010, 01:25:04 pm ---Thank You sooo much
+rep
but in Q21, why is D wrong????
and in que. 19 comp.II also has a double bond , so is it chiral or no????
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thanks for the +rep
metal ion cannot catalyse the reaction.this reaction depends on light!! maybe increasing light intensity can increase rate of reaction but not use of a metal catalyst.
and in q19 it is most definitely chiral if both the Br and I are attached to the carbon which is not involved in the double bond as this carbon will be attached to 4 different groups, H, Br, I and CHCH2 :D
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