1. O/N 2021/P12/Q36
Two isomers are shown.
Which statements about these isomers are correct?
1 They have the same empirical formula.
2 They have different molecular formulae.
3 They are members of the same homologous series.
A 1, 2 and 3
B 1 and 3 only
C 1 only
D 2 and 3 only.
Answer: B
Explaination
Both are the structures of alkane homologous series, they are isomers of each other having same molecular formula but different structural formula. Both the compounds have same ratio and type of atoms so they have the same empirical formula also.
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O/N 2020/P12/Q4, O/N 2020/P11/Q4
Petroleum (crude oil) is separated into useful fractions by fractional distillation. The positions at which fractions X and Y are collected from the fractionating column are shown.
Which statement is correct?
A The temperature increases up the column.
B X condenses at a lower temperature than Y.
C X has a higher boiling point than Y.
D X has longer chain molecules than Y.
Answer: B
Explaination:
In fractional distillation, those hydrocarbons (few carbon atoms) have low boiling points and are condensed and collected at the top of the fractionating column. The bigger hydrocarbons are collected at the lower sections of the column.
Hence, fraction X is lighter or smaller (small chain HC) than Y (which is heavier with bigger chain HC) that’s why fraction X condensed and collected at the top of the column having low temperature.
O/N 2019/P11/Q8
Which row correctly identifies the different formulae of ethene and of its homologous series?
Answer: A
Explaination
Ethene is the first member of alkene series having “ene” as suffix. The general formula for whole alkene series is CnH2n. We will get the molecular formula for ethene by putting the value of number of carbons (eth=2C) in”n” place so it will be C2H4. The empirical formula will be the half of molecular formula i.e., C2H4/2
